Trailer marker light problems

Highridge · Jul 17, 2006

Mike, the taillights do work, it's just the marker lights. The truck has the heavy tow package from the factory. All I did was add the brake controller.

MikeD74T · Jul 17, 2006

I'm not familiar with any wiring configuration that separates the marker lights from the taillights. Could it be that your getting power from somewhere else that is keeping the taillights on? Do you have trailer brakes with a trailer battery charging wire? I've had grounding problems where directionals don't work but make the taillights flash. Mike

Casco1 · Jul 17, 2006

I have a Chevy with auto-on lights but the trailer tapins at the back are not tied in to that line. I know mine came from the factory with trailer wiring already run to the rear to make it easy for dealer hitch installation. From what you say I'd look for a sad connection or short.

George2615 · Jul 17, 2006

Highridge,
Sounds to me like when you add the trailer lighting to the truck the extra current draw from the additional trailer tail light / side markers is to much for the fuse. The brake lights and turn signals are separate and work independent of the tail lights. When the tail lights and side markers on the truck are lit the ones on the trailer should be too. If you plug in your trailer to the truck and manually turn on the parking lights, does the fuse blow? If so either there is a short in the trailer wiring or the load is too much. I suspect a short or poor ground connection on the trailer wiring. I have auto lights on my Chevy truck and 2 different trailers. All the lights work fine with it.

Highridge · Jul 17, 2006

Mike, if by charging wire you mean for a breakaway battery, then it's got one.
George, before the fuse blows, I can turn the lights on manually.

I'm thinking it's a short but you'd think it would happen when the headlights kick on.

bugstruck · Jul 17, 2006

One way is to check the trailer circuit marker/tail lamps for a grounding of the hot lead, but you have to pull all the bulbs to do that. Otherwise you'll read continuity through the bulb filament. Won't fix a tow vehicle problem but it will let you know the trailer wiring is good. If any of the lights flicker while you're parked you can also check for an intermittent grounded light socket by putting one bulb in at a time in each different location. You should show continuity each time. If you don't, that one isn't making ground, but the simple test on that is the bulb shouldn't light either if the ground is fully open. Lights can obviously flicker on intermittent connections on the hot side too.

But you knew all or most of that I bet

AndyG · Jul 25, 2006

There has been lots of good advice so far. I am going to ask a dumb question. Are you putting the correct size fuse in? The proper size is usually written on the fuse panel. I would also check the owner's manual to make sure that the agree on the size of the fuse. I'm not convinced that you have a short but maybe the circuit is slightly overloaded. It might be a good idea to move up one size (5A) in fuse size to see if this helps. I don't think that one size bigger endanger your electrical system and it might solve your problems. No matter what size you choose I recommend that you replace the fuse with a circuit breaker. They make breakers that fit into the regular fuse slot.

Highbeam · Jul 25, 2006

They do? Auto reset circuit breakers into the standard blade fuse slots? I have an intermittent short in a power lock circuit in my truck that blows 15 amp fuses every few months. I leave the circuit dead now but if there was an auto reset breaker I could put in then that would be great.