Trailer brake controller wiring

Ryan5034 · 07-28-2021, 05:35 PM

couple extra comments to kchan

2. Some trailers have "surge" brakes, which work via the force applied thru the hitch. It's not that smooth or great but meets the law. Generally your trailer has to be braked above 3000#. That's the law around here, there's no inspection for this unless you wreck it.

Other trailers have electric brakes which are way smoother and easier to modulate, those require the external brake controller, whether that is hard wired or wireless is up to you.

Your friend is right on the weights your max capacity is like 1000# payload, that trailer will put you over limit. This is why the X5 isn't a great tow vehical. If you are within the weights you are plenty fine. Most mid size SUV's have similar capacities. You could probably push this number some but probably not enough for what you want. Most people look at the max tow rating of 7200# and hook up any they want and "send it" probably not the best plan.

kchan · 07-28-2021, 07:46 PM

Thank you all for the explanation.

So, if I don't have a brake controller, if I just plug in the trailer 7 pin plug to the car's 7 pin, it won't provide any braking function at all?

For the brake controller, are the connector standard across the industry? For example, I saw the BMW wiring harness Tekonsha 3037-P that is supposed to bridge between the car's brake connector to the brake controller (for example Tekonsha P2). Would this harness work with other brands of controllers?

I don't want to spend couple hundred on some inline unit (like the Curt bluetooth unit), since I am not sure if I will use it again.

Why is there a need for a separate controller to simply control the brakes, would hope that they would include that as part of the towing package...

jad03060 · 07-28-2021, 08:34 PM

With out a brake controller, or surge brakes on the trailer, when you plug the trailer in, all you'll have is light controls...no braking action on the trailer at all. That can overload the vehicle's brakes, and if excessive, cause brake fade, or the trailer deciding to become erratic in some situations which can be quite dangerous. The stability control built into the vehicle that gets activated when in towing mode will only helps so much without brake control. That gets triggered automatically when you plug the trailer in through the electronic towing module (separate from the brake controller). There's usually a little play in the hitch/tongue, so without brakes, when you slow, that can bang and will always be pushing, lengthening your stopping distance.

If you do not have surge brakes, then you'll want a brake controller. WHich one, and how you hook it up...all should end up functional. To work well, you need to calibrate the controller to both the vehicle and the trailer's weight otherwise, you might get more braking than needed on a lightly loaded trailer, causing the brakes to potentially lock up, or not provide much braking capacity if it's too weak.

On a wireless one, you need to pair it so you can get that control...how that ends up, depends on which one you get. The wired one, also needs adjustment, but it's generally all built in, so you won't need your phone, or module to make it all work.

Ryan5034 · 07-28-2021, 09:10 PM

On the wiring side, I have only seen a Tekonsha and a RedArc brake controller both had the same wiring harness, I assume the harness is universal. That said some of them provide the plug and wires, but you have to assembly the connector with wires in the right order. A decent trailer sales place should be able to put you in the right direction here. It's literally the same plug under the dash as a F-150 so it's not hard to them to figure it out.

jad03060 talked about some banging and play with the hitch, if you can find a locking hitch pin like this link below it will get rid of a lot of unnerving noises and racket.

https://www.amazon.com/SHP2040-Keyle...524461&sr=8-50

kchan · 07-29-2021, 09:04 PM

Thank you all for your explanation.

For the harness, has anyone at the end find the correct one?

Earlier someone says the Tekonsha BMW 3037-P harness has wrong pin assignment? If the connector will fit both ends, I can just cut and splice/resolder it. What do you think? At least I don't need to crimp the bare pin and try to fit in the connector housing...

jad03060 · 07-29-2021, 11:54 PM

Quote:

Originally Posted by kchan

Thank you all for your explanation.

For the harness, has anyone at the end find the correct one?

Earlier someone says the Tekonsha BMW 3037-P harness has wrong pin assignment? If the connector will fit both ends, I can just cut and splice/resolder it. What do you think? At least I don't need to crimp the bare pin and try to fit in the connector housing...

Buy the right extractor tool, and just move them!

kchan · 07-30-2021, 04:10 PM

Is there specific pin out info available, and where can I find the pin removal tool?

Why would Tekonsha ship something that doesn't work, and expect user to mess with the wiring? Am I missing something?

jad03060 · 07-30-2021, 06:27 PM

Too bad Fry's closed up shop! You'd probably have found one there.

I don't know the details on the connector, but once you do, finding the tool is fairly easy at least online. Generally, they're not much, either...probably cost more in shipping than the tool, but you might find it on Amazon and get free delivery.

kchan · 08-04-2021, 02:42 AM

Is the brake controller wiring located under the dash (near steering wheel), or is it in the trunk (right rear corner)? Or is it at both places? I popped open the right rear corner carpeted cover, see a bunch of harness but don't seem to see the brake controller connector.

The Tekonsha harness is very long and kind of made me think it's in the rear of the car, but I couldn't find it...

jad03060 · 08-04-2021, 07:41 PM

In the G05, at least in the USA, the brake controller plug is under the dash, probably tied back, and not immediately evident.

While less expensive to use a wired one, if I end up needing one, I'll probably go with a wireless one.

Polo08816 · 08-05-2021, 10:45 AM

Quote:

Originally Posted by jad03060

With out a brake controller, or surge brakes on the trailer, when you plug the trailer in, all you'll have is light controls...no braking action on the trailer at all. That can overload the vehicle's brakes, and if excessive, cause brake fade, or the trailer deciding to become erratic in some situations which can be quite dangerous. The stability control built into the vehicle that gets activated when in towing mode will only helps so much without brake control. That gets triggered automatically when you plug the trailer in through the electronic towing module (separate from the brake controller). There's usually a little play in the hitch/tongue, so without brakes, when you slow, that can bang and will always be pushing, lengthening your stopping distance.

If you do not have surge brakes, then you'll want a brake controller. WHich one, and how you hook it up...all should end up functional. To work well, you need to calibrate the controller to both the vehicle and the trailer's weight otherwise, you might get more braking than needed on a lightly loaded trailer, causing the brakes to potentially lock up, or not provide much braking capacity if it's too weak.

On a wireless one, you need to pair it so you can get that control...how that ends up, depends on which one you get. The wired one, also needs adjustment, but it's generally all built in, so you won't need your phone, or module to make it all work.

I don't understand why BMW didn't make a trailer brake controller a standard feature or at least an option.

Honestly, for towing applications, you're probably better off with a full size domestic SUV like a GM Tahoe/Suburban or Ford Expedition platform vehicle.

jad03060 · 08-05-2021, 03:59 PM

What gets me is that where the plug interface is, there's no good place to mount the controller. If I decide to tow something that needs trailer brake control, I'll probably buy a wireless controller. That has the advantage of being easily transportable when I sell the vehicle, too. Now, which one of the several available, I haven't decided.

brucesallen · 09-29-2021, 02:04 PM

Has anyone fitted the 2022 M5 45e with trailer brake controller and wiring for lighting? By inspection I have found that there is no connector under the front dash or in the right rear of trunk for a trailer brake controller. Also, I determined that there are only two wires going to the 7-pin rear plug for the trailer. Power and Ground. No connections are made for trailer lights, or left and right brake/signal lights. This means that if I install a bluetooth brake controller I still will not have any trailer lights! Looks like BMW has made trailer towing near impossible and a major project to install.

jad03060 · 09-29-2021, 08:55 PM

In the USA, BMW no longer does the trailer make ready. Earlier X5 series (and most?) of the others were setup from the factory so retrofitting a hitch and electronics was fairly easy...that's not true today, at least in the USA.

If you do have the factory towing package, it does NOT include an electronic brake controller, but supposedly, there's a plug for one buried under the dash by the driver's left knee. I haven't looked for it on mine, but some have found it and used in on the G05.

brucesallen · 09-30-2021, 03:01 PM

I looked under the dash as I saw in this forum pictures No connector there. Further, I looked at the 7 pin external trailer connector and only two pins are wired. Power and ground. So nothing comes from the M5 for trailer brake controller or running lights or stop and turn lights. SO even the radio control brake controllers would leave me with no lights or stop lights on the trailer. Not legal.

jad03060 · 09-30-2021, 03:12 PM

To be honest, I've not looked for the plug under the dash. Others have said that it is tied back into the harness, and it's not an easy find, but it was there.

As to the other wiring to the 7-pin plug...I've not plugged anything into mine (yet!), but if you got the OEM towing package, you probably should complain to the dealer...it should have everything necessary to pull a trailer that does not require trailer brakes, which includes the lights for both running, turn, and stop.

If it's an aftermarket towing setup, all bets are off. While there are adapters that will give you the lights, they do not include the brake controller, or integration to the stability control, PDC cutout, or camera options.

So, was the towing package from the factory, or maybe a dealer add-on? An add-on is a lot of labor and the parts aren't cheap, either.

As sold in the USA, the G05 no longer comes with the towing prep where everything is fairly easy to retrofit.

brucesallen · 09-30-2021, 03:23 PM

I special ordered the factory trailer option in order to be ready to tow. No lighting wiring. Only power and ground terminals used on 7 pin connector.

jad03060 · 09-30-2021, 03:30 PM

Quote:

Originally Posted by brucesallen

I special ordered the factory trailer option in order to be ready to tow. No lighting wiring. Only power and ground terminals used on 7 pin connector.

IMHO, somebody messed up and it is a warranty issue for BMW to resolve for you. Out of the box, it should be able to tow an unbraked (i.,e., fairly light) trailer legally. I don't remember the unbraked weight limit, but it's somewhere around 1600# or so. Should be listed in your manual and maybe on the placard by the door.

brucesallen · 09-30-2021, 03:51 PM

You make sense. Factory error. Illegal connector install even for lightweight trailers. I have a call into my local BMW service people who have promised to look up the 7 pin wiring for my 2022 45e in the shop manual schematic. If it shows more than two pins wired then they built it incorrectly.

brucesallen · 09-30-2021, 04:40 PM

HAH! my local BMW dealer service manager just emailed the schematic of the 7 pin connector and associated Trailer Module. It shows all pins wired and other cable harnesses to bring inside the car. This is a schematic for MY VIN! Looks like a manufacturing screw up. Dealer service man wants to see it tomorrow. Progress.

brucesallen · 10-01-2021, 10:05 AM

I went to the dealer this morning. I was wrong. All 7 pins are wired and then I plugged in my trailer and all lights worked properly. This still leaves open the question as to where the brake control wire goes in the X5 and how do I connect a brake controller to it?

jad03060 · 10-01-2021, 01:25 PM

Others have said the connector is tied up in the harness and they had to cut some lacing to free it up.

07-28-2021, 05:35 PM	#89
Ryan5034 First Lieutenant 83 Rep 360 Posts Drives: 2019 X5 50i Join Date: Jun 2016 Location: Fargo, ND iTrader: (1) Garage List 2019 BMW X5 xdrive50 [0.00] [0.00] 2011 BMW X5 xdrive 50 [0.00] 1964 Chevrolet Bel-Air [0.00]	couple extra comments to kchan 2. Some trailers have "surge" brakes, which work via the force applied thru the hitch. It's not that smooth or great but meets the law. Generally your trailer has to be braked above 3000#. That's the law around here, there's no inspection for this unless you wreck it. Other trailers have electric brakes which are way smoother and easier to modulate, those require the external brake controller, whether that is hard wired or wireless is up to you. Your friend is right on the weights your max capacity is like 1000# payload, that trailer will put you over limit. This is why the X5 isn't a great tow vehical. If you are within the weights you are plenty fine. Most mid size SUV's have similar capacities. You could probably push this number some but probably not enough for what you want. Most people look at the max tow rating of 7200# and hook up any they want and "send it" probably not the best plan.
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07-28-2021, 07:46 PM	#90
kchan Private First Class 39 Rep 129 Posts Drives: 2018 F80 ZCP Join Date: Nov 2017 Location: Fremont, CA iTrader: (0)	Thank you all for the explanation. So, if I don't have a brake controller, if I just plug in the trailer 7 pin plug to the car's 7 pin, it won't provide any braking function at all? For the brake controller, are the connector standard across the industry? For example, I saw the BMW wiring harness Tekonsha 3037-P that is supposed to bridge between the car's brake connector to the brake controller (for example Tekonsha P2). Would this harness work with other brands of controllers? I don't want to spend couple hundred on some inline unit (like the Curt bluetooth unit), since I am not sure if I will use it again. Why is there a need for a separate controller to simply control the brakes, would hope that they would include that as part of the towing package...
	Appreciate 0 Quote

07-28-2021, 08:34 PM	#91
jad03060 Major General 3166 Rep 6,805 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	With out a brake controller, or surge brakes on the trailer, when you plug the trailer in, all you'll have is light controls...no braking action on the trailer at all. That can overload the vehicle's brakes, and if excessive, cause brake fade, or the trailer deciding to become erratic in some situations which can be quite dangerous. The stability control built into the vehicle that gets activated when in towing mode will only helps so much without brake control. That gets triggered automatically when you plug the trailer in through the electronic towing module (separate from the brake controller). There's usually a little play in the hitch/tongue, so without brakes, when you slow, that can bang and will always be pushing, lengthening your stopping distance. If you do not have surge brakes, then you'll want a brake controller. WHich one, and how you hook it up...all should end up functional. To work well, you need to calibrate the controller to both the vehicle and the trailer's weight otherwise, you might get more braking than needed on a lightly loaded trailer, causing the brakes to potentially lock up, or not provide much braking capacity if it's too weak. On a wireless one, you need to pair it so you can get that control...how that ends up, depends on which one you get. The wired one, also needs adjustment, but it's generally all built in, so you won't need your phone, or module to make it all work.
	Appreciate 0 Quote

07-28-2021, 09:10 PM	#92
Ryan5034 First Lieutenant 83 Rep 360 Posts Drives: 2019 X5 50i Join Date: Jun 2016 Location: Fargo, ND iTrader: (1) Garage List 2019 BMW X5 xdrive50 [0.00] [0.00] 2011 BMW X5 xdrive 50 [0.00] 1964 Chevrolet Bel-Air [0.00]	On the wiring side, I have only seen a Tekonsha and a RedArc brake controller both had the same wiring harness, I assume the harness is universal. That said some of them provide the plug and wires, but you have to assembly the connector with wires in the right order. A decent trailer sales place should be able to put you in the right direction here. It's literally the same plug under the dash as a F-150 so it's not hard to them to figure it out. jad03060 talked about some banging and play with the hitch, if you can find a locking hitch pin like this link below it will get rid of a lot of unnerving noises and racket. https://www.amazon.com/SHP2040-Keyle...524461&sr=8-50
	Appreciate 0 Quote

07-29-2021, 09:04 PM	#93
kchan Private First Class 39 Rep 129 Posts Drives: 2018 F80 ZCP Join Date: Nov 2017 Location: Fremont, CA iTrader: (0)	Thank you all for your explanation. For the harness, has anyone at the end find the correct one? Earlier someone says the Tekonsha BMW 3037-P harness has wrong pin assignment? If the connector will fit both ends, I can just cut and splice/resolder it. What do you think? At least I don't need to crimp the bare pin and try to fit in the connector housing...
	Appreciate 0 Quote

07-30-2021, 04:10 PM	#95
kchan Private First Class 39 Rep 129 Posts Drives: 2018 F80 ZCP Join Date: Nov 2017 Location: Fremont, CA iTrader: (0)	Is there specific pin out info available, and where can I find the pin removal tool? Why would Tekonsha ship something that doesn't work, and expect user to mess with the wiring? Am I missing something?
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07-30-2021, 06:27 PM	#96
jad03060 Major General 3166 Rep 6,805 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	Too bad Fry's closed up shop! You'd probably have found one there. I don't know the details on the connector, but once you do, finding the tool is fairly easy at least online. Generally, they're not much, either...probably cost more in shipping than the tool, but you might find it on Amazon and get free delivery.
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08-04-2021, 02:42 AM	#97
kchan Private First Class 39 Rep 129 Posts Drives: 2018 F80 ZCP Join Date: Nov 2017 Location: Fremont, CA iTrader: (0)	Is the brake controller wiring located under the dash (near steering wheel), or is it in the trunk (right rear corner)? Or is it at both places? I popped open the right rear corner carpeted cover, see a bunch of harness but don't seem to see the brake controller connector. The Tekonsha harness is very long and kind of made me think it's in the rear of the car, but I couldn't find it...
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08-04-2021, 07:41 PM	#98
jad03060 Major General 3166 Rep 6,805 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	In the G05, at least in the USA, the brake controller plug is under the dash, probably tied back, and not immediately evident. While less expensive to use a wired one, if I end up needing one, I'll probably go with a wireless one.
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08-05-2021, 03:59 PM	#100
jad03060 Major General 3166 Rep 6,805 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	What gets me is that where the plug interface is, there's no good place to mount the controller. If I decide to tow something that needs trailer brake control, I'll probably buy a wireless controller. That has the advantage of being easily transportable when I sell the vehicle, too. Now, which one of the several available, I haven't decided.
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09-29-2021, 02:04 PM	#101
brucesallen New Member 0 Rep 8 Posts Drives: BME 2022 X5 45e Join Date: Sep 2021 Location: NH iTrader: (0)	2022 M5 45e plug in hybrid Has anyone fitted the 2022 M5 45e with trailer brake controller and wiring for lighting? By inspection I have found that there is no connector under the front dash or in the right rear of trunk for a trailer brake controller. Also, I determined that there are only two wires going to the 7-pin rear plug for the trailer. Power and Ground. No connections are made for trailer lights, or left and right brake/signal lights. This means that if I install a bluetooth brake controller I still will not have any trailer lights! Looks like BMW has made trailer towing near impossible and a major project to install.
	Appreciate 0 Quote

09-29-2021, 08:55 PM	#102
jad03060 Major General 3166 Rep 6,805 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	In the USA, BMW no longer does the trailer make ready. Earlier X5 series (and most?) of the others were setup from the factory so retrofitting a hitch and electronics was fairly easy...that's not true today, at least in the USA. If you do have the factory towing package, it does NOT include an electronic brake controller, but supposedly, there's a plug for one buried under the dash by the driver's left knee. I haven't looked for it on mine, but some have found it and used in on the G05.
	Appreciate 0 Quote

09-30-2021, 03:01 PM	#103
brucesallen New Member 0 Rep 8 Posts Drives: BME 2022 X5 45e Join Date: Sep 2021 Location: NH iTrader: (0)	2022 M5 45e plug in hybrid I looked under the dash as I saw in this forum pictures No connector there. Further, I looked at the 7 pin external trailer connector and only two pins are wired. Power and ground. So nothing comes from the M5 for trailer brake controller or running lights or stop and turn lights. SO even the radio control brake controllers would leave me with no lights or stop lights on the trailer. Not legal.
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09-30-2021, 03:12 PM	#104
jad03060 Major General 3166 Rep 6,805 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	To be honest, I've not looked for the plug under the dash. Others have said that it is tied back into the harness, and it's not an easy find, but it was there. As to the other wiring to the 7-pin plug...I've not plugged anything into mine (yet!), but if you got the OEM towing package, you probably should complain to the dealer...it should have everything necessary to pull a trailer that does not require trailer brakes, which includes the lights for both running, turn, and stop. If it's an aftermarket towing setup, all bets are off. While there are adapters that will give you the lights, they do not include the brake controller, or integration to the stability control, PDC cutout, or camera options. So, was the towing package from the factory, or maybe a dealer add-on? An add-on is a lot of labor and the parts aren't cheap, either. As sold in the USA, the G05 no longer comes with the towing prep where everything is fairly easy to retrofit.
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09-30-2021, 03:23 PM	#105
brucesallen New Member 0 Rep 8 Posts Drives: BME 2022 X5 45e Join Date: Sep 2021 Location: NH iTrader: (0)	2022 M5 45e plug in hybrid I special ordered the factory trailer option in order to be ready to tow. No lighting wiring. Only power and ground terminals used on 7 pin connector.
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09-30-2021, 03:51 PM	#107
brucesallen New Member 0 Rep 8 Posts Drives: BME 2022 X5 45e Join Date: Sep 2021 Location: NH iTrader: (0)	2022 M5 45e plug in hybrid You make sense. Factory error. Illegal connector install even for lightweight trailers. I have a call into my local BMW service people who have promised to look up the 7 pin wiring for my 2022 45e in the shop manual schematic. If it shows more than two pins wired then they built it incorrectly.
	Appreciate 0 Quote

09-30-2021, 04:40 PM	#108
brucesallen New Member 0 Rep 8 Posts Drives: BME 2022 X5 45e Join Date: Sep 2021 Location: NH iTrader: (0)	2022 M5 45e plug in hybrid HAH! my local BMW dealer service manager just emailed the schematic of the 7 pin connector and associated Trailer Module. It shows all pins wired and other cable harnesses to bring inside the car. This is a schematic for MY VIN! Looks like a manufacturing screw up. Dealer service man wants to see it tomorrow. Progress. Attached Images
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10-01-2021, 10:05 AM	#109
brucesallen New Member 0 Rep 8 Posts Drives: BME 2022 X5 45e Join Date: Sep 2021 Location: NH iTrader: (0)	2022 M5 45e plug in hybrid I went to the dealer this morning. I was wrong. All 7 pins are wired and then I plugged in my trailer and all lights worked properly. This still leaves open the question as to where the brake control wire goes in the X5 and how do I connect a brake controller to it?
	Appreciate 0 Quote

10-01-2021, 01:25 PM	#110
jad03060 Major General 3166 Rep 6,805 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	Others have said the connector is tied up in the harness and they had to cut some lacing to free it up.
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