How to troubleshoot trailer lights from truck
Thread Starter
Member
Joined: Apr 2007
Posts: 97
Likes: 1
From: Doylestown (Bucks County) PA
2015 ML250, 06 E320 CDI, 2008 GL320 (sold)
How to troubleshoot trailer lights from truck
I typically tow in the winter months and don't remember any trailer light problems. Borrowed a trailer last week (LED lights) and the tail lights are on all the time (even with car off...shuts off in about 15 minutes) and get nothing from the brakes lights or hazards.
When I check the plug (7 pin to 4 pin adapter), I get 3 volts out of the brake light pin and 12 volts out the the turn signal pin (with nothing in the car turned on). The turn signal lights don't light up with the 12 volts so must be no amperage from the turn signal pins.
Checked the lights on the trailer and they all worked fine. I understand I should have bought a resister plug for running LED lights so wonder if I blew a relay?
Ended up driving the trip with just the tail lights on.
So what am I looking for here? Relay?
Thanks,
Ed
When I check the plug (7 pin to 4 pin adapter), I get 3 volts out of the brake light pin and 12 volts out the the turn signal pin (with nothing in the car turned on). The turn signal lights don't light up with the 12 volts so must be no amperage from the turn signal pins.
Checked the lights on the trailer and they all worked fine. I understand I should have bought a resister plug for running LED lights so wonder if I blew a relay?
Ended up driving the trip with just the tail lights on.
So what am I looking for here? Relay?
Thanks,
Ed
Senior Member
Joined: May 2013
Posts: 437
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From: Espoo, Finland
2012 GL 350
First thing I would do with a borrowed trailer is confirm that the pins (on the trailer) are really what you think they are. Then confirm that your adapter is doing what you think it should be doing. It sounds to me like you are sending power to the wrong places.
I've never had a trailer do something like this; most of the time I'm trying to figure out why the various stuff *won't* come on, not why it won't turn off.
I've never had a trailer do something like this; most of the time I'm trying to figure out why the various stuff *won't* come on, not why it won't turn off.
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Joined: May 2008
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From: Overland Park, KS
‘24 BMW iX M60
I tried towing a UHaul trailer with LED lights with our '08 GL and the same thing happened. My SA tells me that it was not built with the capability to tow a trailer with LED lights due to differing 'resistance'. There is an adapter that others have mentioned works however; hopefully someone will pipe in soon.
Bish
Bish
Thread Starter
Member
Joined: Apr 2007
Posts: 97
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From: Doylestown (Bucks County) PA
2015 ML250, 06 E320 CDI, 2008 GL320 (sold)
So I check the trailer with a 12v source and the lights worked as expected....all the led lights worked.
Went to my adapter and found 3-4 v on the night time driving lights but it lite up the the tail lights only and no blinkers. When I first connected it the driving lights on the trailer flashed for a while and then stopped. Thats when I first found out I had a problem.
Anyway, they do make an adapter with a built in resister to be used w LED trailers. My question is how to get my truck trailer adapter to work again. I going to pull my snowmobile trailer this weekend and afraid I'll have no lights.
Went to my adapter and found 3-4 v on the night time driving lights but it lite up the the tail lights only and no blinkers. When I first connected it the driving lights on the trailer flashed for a while and then stopped. Thats when I first found out I had a problem.
Anyway, they do make an adapter with a built in resister to be used w LED trailers. My question is how to get my truck trailer adapter to work again. I going to pull my snowmobile trailer this weekend and afraid I'll have no lights.
Thread Starter
Member
Joined: Apr 2007
Posts: 97
Likes: 1
From: Doylestown (Bucks County) PA
2015 ML250, 06 E320 CDI, 2008 GL320 (sold)
As I was typing the above had another thought....
the 12v coming out the turn signal lights are probably powering the stop trailer lamps since all the clearance lights are off...but the lights are not bright (like you expect for a stop light).
The 3-4 volts coming out of the night time driving lights are not powering anything since the clearance lights are off.
Sure its a blow relay or something....
the 12v coming out the turn signal lights are probably powering the stop trailer lamps since all the clearance lights are off...but the lights are not bright (like you expect for a stop light).
The 3-4 volts coming out of the night time driving lights are not powering anything since the clearance lights are off.
Sure its a blow relay or something....
