Reverse lights in tow connection?

**dougl4246** · 09-21-2006, 08:55 AM

I had the dealer install the tow hitch and light connector when we bought our 06 XC90 about a year ago knowing we would be buying a boat soon. Well that day has come and everything was great until I tried to back the boat up the driveway. Every time I backed up the surge breaks on the trailer would engage. After a lot of head scratching (and some bad language) my neighbor and I figured out that the trailer brakes are supposed to be disabled when the vehicle is put in reverse for just this reason. The trailer is keying off the reverse signal coming from the vehicle to indicate that the vehicle is backing up, makes sense to me..

The problem is that there is NO reverse signal being sent from the vehicle through the wiring harness (7-pin connector) to the trailer, so it doesn't know the vehicle is in reverse. I took it to the dealer today and was told that this is the way Volvo engineered it and he's looking for a "fix". He even said that reverse lights on trailers are not required by law (I found that hard to believe). I asked him if he's ever seen this problem before and he said no. I can not believe that I am the only one in our area with an XC90 that tows a trailer with surge brakes that needs to reverse up hill (can even happen on flat ground).

Does anyone else out there with an XC90 and dealer installed hitch/wire harness tow a trailer with surge brakes? I have to declare BS on the dealer. I think they just installed it improperly, which is fine just fix it and don't give me excuses that this is the way Volvo designed it.

Arggg... And to boot, $270 for the 15K mile service (oil change, tire rotation/balance and a new cabin air filter)

**Big** · 09-21-2006, 11:00 AM

I can't help with the specifics of using surge brakes but I do know that the Volvo trailer harness has no brake line which would normally go to pin 2. That's something that has to be wired separately if you use trailer brakes.

If memory serves correctly there are a couple of types of surge brakes, one of which requires a signal from the car when backing and one that operates independently by detecting the reverse rotation of the trailer wheel. Evidently you have the first type although I believe that even when backing the brakes still offer some resistance--roughly a fifth of maximum--for safety.

There are several people here who tow big boat trailers so maybe they will step up with specifics on how they dealt with this. Good luck!

**dougl4246** · 09-21-2006, 11:33 AM

thanks Big. The brake lights seem to work fine.. The surge brakes engage when there is pressure from the trailer against the hitch ball (assuming that the vehicle is breaking and the trailer is pushing against it). So backing up hill will produce that pressure that engages the brakes. The trailer manual says that the brakes are disabled when the reverse signal is recieved. Fliping around the 7pin to 5 pin connector to connect the running light from the xc90 to the reverse light of the trailer allows me to back it up, not what I would call ideal..

Cheers,
Doug

**Jake529** · 09-21-2006, 09:25 PM

I have 7 cars, 2 Volvo's 1 Grand Marquis, 1 BMW, 1 Chevy El Camino, 1 Ford F-150 and a Cadillac Coupe Deville. I made freinds with the guys at Town Fair Tire, they will rotate my cars tires for free along with flat repairs. If you go in there and have something done to any car they will take care of all your cars. Now, to have the Volvo dealer rotate my tires would cost me way to much money... I tip the kid at the garage 10 bucks and they will balance the tires for free...... Cabin air cleaner 2o bucks at autozone......

Jake

**dmd** · 09-23-2006, 09:39 AM

Originally Posted by dougl4246

thanks Big. The brake lights seem to work fine.. The surge brakes engage when there is pressure from the trailer against the hitch ball (assuming that the vehicle is breaking and the trailer is pushing against it). So backing up hill will produce that pressure that engages the brakes. The trailer manual says that the brakes are disabled when the reverse signal is recieved. Fliping around the 7pin to 5 pin connector to connect the running light from the xc90 to the reverse light of the trailer allows me to back it up, not what I would call ideal..

Cheers,
Doug

I fyou use the running lights, then when the ligts are on you will have no brakes... Just use the 12v power pin. Put a switch from it to the backup on the trailer. When backing uphill, just get out and flip the switch installed on the trailer. Not the best, but can be done easy.

**dougl4246** · 09-27-2006, 02:16 PM

It took the dealer a while but they finally fixed it, they had to hardwire it in after the RIM (or is it REM?), checked it today and it works fine. According to the service guy they called around to a few of the local hitch installers and none of them would touch the wiring on the XC90 said it was too much of a pain. Not a very good design by Volvo for a vehicle that supposed to be able to tow a good sized load if you ask me.

**dmd** · 09-28-2006, 08:26 AM

The demand for a reverse light in towing is so low that it wouldnt be considered. Average loads behind a XC90 wouldnt need brakes, and most
X90's dont tow at all.

**dougl4246** · 09-28-2006, 08:52 AM

I gotta agree that most XC-90's don't tow, but most of the used boats I was looking at in the 19'-20' (3300-4000lbs) range came with brake's. Regardless of the brakes, it seems like a good idea to have reverse lights on the trailer that work. I just find it hard to believe that a $40K SUV wouldn't have a 50cent wire connection. I guess if thats the only compliant I have so far I shouldn't complain...

**AWD*V70XC** · 09-28-2006, 10:14 AM

In defence of the rear reversing light coming on when using a trailer, the reason it does not come on is because, if you reverse back when you have a box trailer on you could blind yourself with the back glare, therefore the lights are turned off.