S0C9

I know this has been addressed before, but I've not found a response for my particular issue - and I've searched this forum and the internet extensively !!

Basically, my '98 F150's trailer running lights do NOT work !
Turn [left + right] lights and stop lights work fine.
Fuses - in engine [all 3 locations] and under dash are all good.
It's not the trailer lights.. tested with friends truck and they work fine, so I know problem is on my truck.

Took 7-pin connector assembly on truck apart, put voltmeter across ground and left [then right] turn/stop pins and get voltage [24v IIRC]. Pulses when flashing. No voltage across ground and running lights wire [brown]. All flat pins in outlet look fine, no corrosion. I do have a + connector (registers voltage too) too, but its not used in a 7-4 pin adapter.

Truck has a standard 7-pin connector and I'm using an adapter to go to 4-pin on trailer. Was working before [for 11 months I've had trailer], then suddenly quit. This would indicate a ground or relay problem, but I can find not evidence of a bad ground, and have no idea if a relay is even involved in this circuit [or not].

Anyone dealt with this before or got additional troubleshooting suggestions..???
I've been fairly thorough and methodical, but I can't find the problem...!!

TIA,
sock

S0C9

Additional research has indicated that there are relays in the "power distribution box" for running lamps, backup lamps, trailer battery and left/right turn lamps..

The hunt continues

dewman

Have you thought to test the 7 to 4 adapter? Maybe something went bad inside it and there is nothing wrong with your truck.

And, welcome to the board!

iowaredneck

I would have to agree that the adapter maybe bad. That is what I would try first. Good luck and welcome aboard.

Good old Bill

Like your method of testing. Not sure if you tried this or not, did you ohm out the negative pin to ground. Am thinking of a backfeed ground in the t/s portion of your test. We know the 4 pin flat trailer connector works (buddies truck). Perhaps the brown (running lites) has no ground to show voltage. Test it also to a seperate ground, if you show voltage to a seperate ground then all is good except the black wire in the 7 pin connector. Am going to check my 02 diagram for additional info. Found something in my diagram, the 7 pin connector for ground uses a white wire. (Strange). Yes in my 02 there is a trailer tow parking lamp relay along with two others for reversing lamps, and battery charge relay. These are located in the battery junction box. Good luck finding that.

S0C9

Thanks Bill [and the others],
yeah the ground is WHITE on my '98, and I did NOT ohm out the negative pin to ground.. but.. given that the turn and stop lights work [and it's a common negative I believe], I would expect that to be good. I have not tested the brown/white to separate ground either, so that I will try too.

It's not the trailer lights.. those are good [tested w/ buddies truck].
I don't think it's the adapter either, 'cus I took it apart and it's all wired up correctly. And I have a 2nd [spare] that has same issue, so it's unlikely that 2 produce same [bad] result.

The thing that struck me during my analysis was that there appears to be no voltage to the brown/white [running lights] wire on the truck side - with or without the adapter and trailer disconnected.
No power, no lights !!

The fuses - based on wiring diagrams and OM - are all good. So if your recommended tests are good, then I think one of 2 things.
1. A bad relay - not working when truck lights are switched on, or
2. A broken wire [not shorted or fuses would be blowing].

thanks,
Sock

PS: There are actually THREE power distro boxes on drivers side under hood on my 5.4L '98
The main one [big and mini fuses + relays], 2nd with relays only, and 3rd with mini fuses only.
The 2nd contains about 7 relays - all same number/type - but no labeling on box lid [or elsewhere] as to what each one is..and (from my understandiung) is the one that contains the "a trailer tow parking lamp relay along with two others for reversing lamps, and battery charge relay", etc. !!!

S0C9

Hey guys,
thanks for suggestions and help... finally figured this booger out !!
It was [as I concluded] a bad relay.. it lives in the secondary power distribution box on the drivers side, between main box and firewall.

In case I can prevent someone else going thru this effort, I've attached a pic of the layout and provided what I know about the relays - identifying numbers, etc in the two blue boxes in the middle. All SIX of the blue relays are identical.

2 of the 3 blue relays that are not labeled [but contain descriptor text] are the Trailer battery charger and Backup lights relays. I do not know which is which, as I do not have either wired for on my truck/trailer. I do not know what the 3rd, nor the two large relays are for.

Cheers,
Sock

airwolf

can you test a Relay to see if its good? local auto parts store did not carry them,,,,

1998 f150 no turn signals,brakes lights or flashers on trailer.Running lights work............

S0C9

Top two relays in diagram above are Left and right turn and stop lights.
Those with blue boxes are all SAME relay, so you should be able to swap any of them around and figure out if the problem is with the relay or not !

I'd check all my fuses first.. if all look good, take the running lights relay and move it to the Left or Right position and see if they start to work. If so, you have a bad relay. If it still doesn't work, its not the relay. Check the hitch coupler and the bulbs !

rlawns

I have a 2000 f150 does anyone no the fuse location for the trailer running lights?

Thanks Rick