I can't get my trailer lights to work. The emergency flasher lights will work but the tail, all of the other lights, brake lights, all don't work.

I checked the fuses on the trailer and they are fine.

Any Ideas where to start?

The truck lights are all working normally.

 

Start by checking the output of the truck using a test light. Usually, if the flashers work, the brake lights should work also.

 

I was looking for the schematic not sure where one is for the 7 pin.

I think the middle is the ground but thats about all I know.

 

If you use a test lite , that will tell you if power gets to the plug , then just match your trailer to that .

 

If the flashers work and the brake lights don't, the problem is on the truck, presuming the trailer has standard wiring and lights. The flashers just flash the brake lights, so you have proved the trailer's brake lights are working.

Did the truck/trailer combination use to work, or is this a new combintation that has never worked?

 

it used yo work....i was told yjere is some kind of device on the truck that might cause this problem....isdeas?

 

Check the output at the truck plug.

 

As far as I can tell the common point is the front control module (FCM), which controls the trailer turn signal relays. Obviously, they are working for the emergency flasher, but nothing else. There is a logic circuit inside the FCM. Either it is defective, or it is getting bogus information over the PCI bus.

The FCM also controls the trailer tail light relay.

This is for the '05. I don't know if your year is the same.

Edit: You might try disconnecting both battery negatives and letting it sit for a half hour or so. That should reboot the processor and clean the RAM in the FCM. It can't hurt.

 

according to wiring diagram check fuse 46 and 47. They power the relays for the turn signals. If you can't find the fuses then you need to check at the rear of truck using the diagram http://www.etrailer.com/faq_wiring.aspx . The relays are in the IPM (intregerated power module)2004) As treefarm said if you are not getting turn signals or brake lights then the IPM or FCM (I think are the same thing) is where your problem is. New part not cheap.

 

If his truck is wired the same as mine, fuses 46 and 47 must be good or the emergency flashers wouldn't work on the trailer, and it seems nonproductive to check at the connector with them working. The problem must lie elsewhere.

The FCM is either inside or fastened to the IPM, if I am reading the manual correctly.

It may not be the FCM. If the info on the PCI bus is bogus, that may be the problem. I haven't had time to chase it down, but I suspect the info originates in the gauge cluster. The problem could be there also. It would take a scan tool to tell.

 

Treefarm you right about the fuses, looking at the diagram the FCM controls the relays in the IPM. But if using the flashers lights his trailer lights then the problem is farther back into the FCM. If the PCI bus is bogus then I would would think he should have other lighting problems?

Edit: doing a quick search on trailer light problems, the major problem has been IPM is blown $400+, the flasher thing is the only item throwing this off.

 

Well I took the truck in and they tested it....said it was fine...Then I took it another place...they tested the plug also....it is fine..

The proeblem is in the trailer.

How can my emergency flshers work but nothging else....

 

Can you get someone else to hook to the trailer and see if you get the same result; flashers only?

 

Go to a trailer store and spend the $20 for a new female 7 way plug (trailer end). I fought wires for days and weeks to spend 20 minutes changing the plug end. It didn't look bad but once I took the cover off you could see all the corrosion on the inside.

My .02

Good luck.

 

Trailer plug x2