I have joined the tail chasing party on this one too!

Thread still pays off!! Thanks for the info!! FIXED!! Weehoo

Now to look at the trailer and see why it blew in the first place - seems like a never ending battle with trailer wiring.

 

Glad to see others are still finding the info useful.

This thread did not get it added to it, but here is the picture of projectSHO89' under hood. I added the text to what is what from his ACSII line art.



Do a file save as from that picture, and keep it around in case you have a question about the relays. They are not documented too well in the owners manual.

 

I have the same problem as these others. I checked fuses including 20amp mini fuse. Still no brake/turn trailer lights. Any other suggestions?

 

what are you using to test the L&R Stop / Turn circuits at the trailer tow adapter ?
- Should be using a test light or meter to a known good ground.

How did you check the fuse ?

Fuse #2, 20A is hot at all times, so with the fuse installed, use a meter or test light to check the pins on the back of the fuse to a known good ground.

You should have + VDC on each side.

If you do not have power on either side, check the Power Dist Box, Fuse #16, 40A ( I would suspect other items do not work if this is blown ).

If the fuse tests good, next is to pull the Left and Right Stop / Turn relays and check that the power is present there.

Pin #3 in the relay socket will have power with the fuse #2 installed.



You can jumper the normally open contacts and the L & R Stop / Turn circuits in the trailer tow adapter should now show + VDC.

If the jumper tests good, next is to test that the MFS in the truck works correctly.
Pin #1 in the relay socket is the output of the MFS to the coil.
This should flash at the turn signal rate or be solid on when pressing on the brake pedal.

 

Thanks for all the info and detail. I'll try all this today or tomorrow and hopefully write another thank you note!

Jim

 

Well, Sscully, you helped me many years later, on 9/3/2013, with the 20A fuse in the mini box. But that 's only 1/2 my problem. Factory tow package, but I still don't have running lights either. I have replaced all wires on tow dolly back to lamps, and checked the bulbs. now that I replaced the 20A mini fuse the turn signals and brake lights work, but I still don't have running lights. Is there a fuse for that separately?

Where? thanks.

 

Yes, that's a separate fuse. If you don't have an owner's manual you can download it.

 

Yes, the 97/98 has both a relay and a fuse for the parking lamps.

Start with the fuse, Engine compartment Fuse #1 20A ( main fuse panel, no the mini )
- This feeds both the trailer tow parking lamp relay and the trailer tow backup circuit.

The relay for the parking lamps, you can see documented in this thread up in post #17, to check if the relay is at issue after swapping the fuse.

When testing, make sure to use a test light to the ground on the trailer tow adapter, not your trailer as the test light.

 

Thanks so much! Wanted to borrow neighbor's trailer and lights weren't working. Husband and neighbor trouble-shot for 15 min. I said, wait, let me Google it AND first hit had this solution. Neighbor had extra fuse and in less than 5 min. we had lights! Only have had truck for a year and it's 16 years old. Directions to fuse box and "it might still have tape on it" were spot on. Thanks! I really appreciate being able to check online for solutions to issues with the truck.

 

My son tore the trailer plug in of the truck so he cut the wires now there is no lights on the back of the truck its a 98 F1-50

 

I have read this whole thread and still have no running lights or backup lights on the trailer. I have a 98 and my son has a 97 f150 with the same problem.
I have changed the truck tailight harness, rewired the trailer socket direct to the factory harness, ripping out the 3 way harness. I have repaired the main harness that was spliced into and in one wire was rotten. I have perfect tail lights on the truck but only signals and brake on the trailer socket. The black power wire is good, the ground is good.
I have checked #1 fuse and changed it in the main box under the hood. I have changed the #2 fuse in the fender box. These are both delivering power. There is power going to both relays shown in picture on post #17 relay. I traded these two relays back and forth, but have no other way to test them. I bought a new one but no change.
Please help.

 

So I with the running lights on I traded the relay for the relay for the signal lights. This blew the fuse. I changed the fuse and put the old relay back in and am back to square one, though I realize I always had backup light power.
The only thing not working is the running lights to trailer.

 

Thanks! This thread bailed me out in 2016! My undocumented fuse boxes were both taped shut! I should've googled earlier.

 

Worked for me, too - thanks for posting this!