2010 f150 no signals/stop lights on trailer

[Chatty21VLX]

Might be a long shot on this forum, but I have a 2010 f150 that won't light the stop lamps or signals on my trailer. The running lights work, reverse lights work. From my googling the past few days, it looks like there is a single 20 amp fuse and 2 relays that control these lights. I replaced the fuse, which was blown, and still no dice. I can hear the relays clicking, so they're probably good? Anyway, I'm not getting 12v at the pins on the trailer plug. I know the trailer is good because everything worked on my last truck. Any help?

[NHolladay]

Get up under the harness where they connect the trailer light outputs from the taillights make sure all the connections are good.  Get a multimeter and work your way back up the system to see where the issue is.  If it is a Kremlin, you could always just pull new wires directly off taillight leads and just bypass the stuff that is not working.  Assuming there working on the truck. 

[jk13]

What fuse did you replace?

Double check your owner's manual, but what I can find online there are separate fuses for trailer left/stop and right/stop. They are #36 and #42 in the passenger side interior kick panel.

Assuming new-to-you truck from your post, previous owner likely had a janky trailer and simply blew all the fuses.

[Chatty21VLX]

20 minutes ago, jk13 said:

What fuse did you replace?

Double check your owner's manual, but what I can find online there are separate fuses for trailer left/stop and right/stop. They are #36 and #42 in the passenger side interior kick panel.

Assuming new-to-you truck from your post, previous owner likely had a janky trailer and simply blew all the fuses.

Yes, new to me truck. My research has indicated fuse 45 under the hood in the fuse/relay box on top of the radiator. There is no manual in the truck, and so far I haven't seen anything relating to the kick panel fuses. I might be wrong, but I can't see them engineering a fuse to fees 2 relays only to use 2 more fuses after that? Thanks though, at least I can research it.

Edited August 19, 2017 by Chatty21VLX

[Bozboat]

2 hours ago, Chatty21VLX said:

Yes, new to me truck. My research has indicated fuse 45 under the hood in the fuse/relay box on top of the radiator. There is no manual in the truck, and so far I haven't seen anything relating to the kick panel fuses. I might be wrong, but I can't see them engineering a fuse to fees 2 relays only to use 2 more fuses after that? Thanks though, at least I can research it.

Had the same problem on my 2012 F150, fuse is a square in a box on top of the radiator 

The F-150 has many fuses, some under the hood, some in the right kick panel. The trailer light functions are split into several fuses, not just one fuse for trailer lights.

 

Here is a photo of my spare fuse

 

Edited August 19, 2017 by Bozboat

[Chatty21VLX]

@Bozboat where is that one supposed to go? The diagrams I have found that seem to match up with my truck's fuse layout doesn't have a fuse that style that corresponds to the trailer tow package. Do you remember the slot #?

[Bozboat]

[Chatty21VLX]

9 minutes ago, Bozboat said:

Which number slot?

[Bozboat]

I think it is number 73

a 20 amp square on first row (most toward front)

[Bozboat]

[Chatty21VLX]

73 in my box is empty. I found a manual online for supposedly a 2010 model. 73 is not used, and slot 45 is the 20A labeled trailer tow stop turn relay feed. Maybe they changed the configuration sometime between 2010 and newer. I guess I could put a fuse in there and see if anything happens.

[Bozboat]

Just now, Chatty21VLX said:

73 in my box is empty. I found a manual online for supposedly a 2010 model. 73 is not used, and slot 45 is the 20A labeled trailer tow stop turn relay feed. Maybe they changed the configuration sometime between 2010 and newer. I guess I could put a fuse in there and see if anything happens.

Can you pull the fuse in slot 45 and see if it looks ok?

[Chatty21VLX]

34 minutes ago, Bozboat said:

Can you pull the fuse in slot 45 and see if it looks ok?

Yes, already did that. It was blown, I replaced it, and still nothing. The relays might be bad, but I hear them clicking when the signals are on. I guess the only way to be 100% sure would be to test with a known working set of relays.

[Bozboat]

Check the ground wires on the trailer, sometimes you can clean them and reattach them and solve some issues

[jk13]

7 hours ago, Chatty21VLX said:

Yes, already did that. It was blown, I replaced it, and still nothing. The relays might be bad, but I hear them clicking when the signals are on. I guess the only way to be 100% sure would be to test with a known working set of relays.

Relays fail extremely rarely. Pull the two fuses in the kick panel I listed and see if they're blown. 

[Chatty21VLX]

On 8/19/2017 at 11:30 PM, jk13 said:

Relays fail extremely rarely. Pull the two fuses in the kick panel I listed and see if they're blown. 

I finally got around to pulling those 2 fuses. Both were still good. I'm going to be checking the trailer for a short. I only have a 2 mile tow to the ramp, but I've been towing without lights for awhile.

[TomH]

You said originally that you didn't have 12V at those particular pins.  Did you meter it, or were you just assuming since they weren't lighting on the trailer.  If you metered it and don't have the voltage, there's no reason to be looking at the trailer as the problems on truck side.  If you do, then by all means check the trailer.  I took a peek at your manual though, and looks like the right/stop and left/stop fuses are #37 and #38 in the fuse block under the hood, not the kick panel for your year.  If those aren't the ones you checked, I'd start by checking there.

[Chatty21VLX]

21 hours ago, TomH said:

You said originally that you didn't have 12V at those particular pins.  Did you meter it, or were you just assuming since they weren't lighting on the trailer.  If you metered it and don't have the voltage, there's no reason to be looking at the trailer as the problems on truck side.  If you do, then by all means check the trailer.  I took a peek at your manual though, and looks like the right/stop and left/stop fuses are #37 and #38 in the fuse block under the hood, not the kick panel for your year.  If those aren't the ones you checked, I'd start by checking there.

Yes, I was checking the truck pins with a meter. I wasn't getting 12v on the pins for the signals. I will check fuses 37 and 38 tonight.

[robbennett]

Check to see if the new fuse blew. Could happen easily if there's an issue with trailer wiring. 

Edit: Nevermind I see you already did that. There could be a wire on the truck or trailer that the insulation rubbed off of. If the fuses are all good start tracing them. 

 

Edited September 13, 2017 by robbennett

[Bozboat]

On 9/10/2017 at 7:47 PM, Chatty21VLX said:

I finally got around to pulling those 2 fuses. Both were still good. I'm going to be checking the trailer for a short. I only have a 2 mile tow to the ramp, but I've been towing without lights for awhile.

I would start with the ground wires on the trailer.

[malibu2004]

Have you checked your truck with a known good trailer? Has a buddy with a known good truck hooked up to your trailer to see if it works? I wouldn't do anything until you do that. 

[TomH]

He said he didn't have 12V on the truck side, so he needs to start at the truck - be it fuses or wiring.  Not to say that there isn't a short in the trailer wiring that blew the fuses, but he needs to have power on the truck side first.

Agree with Malibu though that, it's a good idea to check your trailer lights with someone else's truck, and then you can verify whether or not the trailer is fine or contributing to the problem.

Edited September 13, 2017 by TomH

[Chatty21VLX]

All good suggestions. Yes, I need to make sure I am getting the 12v on all necessary pins before testing a trailer. I also agree that I need to test with a known good trailer... I'll have to go to my buddy's house and check with his. Maybe I should hook mine up to his vehicle and see if a fuse pops.

[Chatty21VLX]

On 9/12/2017 at 11:37 AM, TomH said:

You said originally that you didn't have 12V at those particular pins.  Did you meter it, or were you just assuming since they weren't lighting on the trailer.  If you metered it and don't have the voltage, there's no reason to be looking at the trailer as the problems on truck side.  If you do, then by all means check the trailer.  I took a peek at your manual though, and looks like the right/stop and left/stop fuses are #37 and #38 in the fuse block under the hood, not the kick panel for your year.  If those aren't the ones you checked, I'd start by checking there.

37 and 38 are relays, not fuses.

[TomH]

You're right, misread it.  Looks like fuse 45 for that one - which you've already replaced.  Are any of the relays in the fuse box the same as the trailer light ones?  If so, swap a known good one in and test it out to figure out if your relays are cooked.  It's possible whatever took out your fuse may have gotten the relays - otherwise, you'll need to start tracing wires - and I'd start at the back of the trailer light plug first.  One other question, does your truck have separate plugs for 4-pin versus 7-pin?  If so, have you metered both for voltage?