smaier

I keep blowing 20 amp fuse # F10 when I hook up my trailer. Fuse #36 for Right turn/brake is OK. Then it mentions #42 fuse for Left Turn/brake and there is no #42 in the fuse panel. Where is that fuse.? I just had trailer wiring totally redone and it still is doing the same. Do I need to worry about R201 relay for tow park lamps. Have 2008 F-150..

techrep

iTrader: (1)

7 pin or 4 pin ??

Mike Vidal

Do you have any auxiliary lights or other accessories wired into your lighting system?
If so, that could be the cause. Sorry, my only idea right now.

PerryB

Check the plug and make sure the. Ground isn't in the wrong position.

smaier

I did find fuse #42 and that was replaced. Now the stop and turn lights work R and L. But when I turn on pickup lights which turns on trailer park lamps it blows the 20 amp trailer park lamp fuse.

nick-f150

I know this is an old thread, and I don't like resurrecting old threads, but this is the only post I can find with my exact problem. @smaier were you ever able to resolve this problem? ! have a 2006 F150 Lariat Crew Cab. When towing my boat trailer with the 5 pin harness (with a 5 pin to 7 pin adapter), while towing at night with the lights on it will blow the 20A fuse number F10. But not immediately. It can work normally all night, then at some point during the drive I will notice the trailer lights out. And I must pull over somewhere to swap out that 20A fuse. That fuse also controls the trailer backup lights (which in my case is needed otherwise the trailer cannot be backed up ... it remains locked). But once I change the fuse the running lights work again and I can back up again. There is no rhyme or reason for the fuse blowing (other than the lights on are when it happens). It can run anywhere from a few hours to all night with no issue, but at some point it will blow again. I rewired the 5 pin harness on the trailer (incase something was loose or shorting) and I also replaced the 5 pin to 7 pin adapter to connect it to my truck. It can work all night, then at some point it just fails. Is there something on the trailer causing this? Or something on the truck? If someone has figured this out it would be awesome if you can post a fix.

ProjectSHO89

Could be the truck (get under there and inspect the wiring at the back end) but I'd wager on an intermittent wiring short to ground on the trailer. Brown wire. Look at any point where the trailer manufacturer may have fed the wiring through the frame, around anything, the light assemblies (including markers). You'll find either a pinched/chafed wire or that one of the lights has an intermittent short circuit.

Worst case, buy a new trailer lighting system (lights, wiring harness, etc) and swap the whole thing out.

nick-f150

Wow. You were spot on.

I originally tested all the connections with a multimeter and everything looked fine. And even verified all the grounds. After reading your reply, I pulled out all the trailer side markers to inspect the cable where they are routed into the trailer…low and behold, when I pulled one particular side marker out, the wire was completely chaffed where it came out of a hole on the steel trailer. There was exposed copper partially touching the metal trailer. I cut out and replaced that section of wire…and now hoping for the best. I do recall seeing that side marker go off and on (and even flicker) in the past, so it doesn’t surprise be that it was that light. Also removed and inspected all the other lights and wires on the trailer. Everything else seems solid. I’ll post a picture of what it looked like when I can.

I’m quite confident that this resolved the issue, and I’ll keep an eye on it now.

Thank you!

ProjectSHO89

Sounds right.

Had the same problem on a boat trailer back in the 90s (1990 production). The trailer manufacturer just drilled holes through the frame and ran the wires through it without any grommet.