F150 4 Prong Trailer Plug

Bill Tattersall · May 17, 2021

Hi guys. My 2012 Ford F150 has the 4 prong trailer plug with the female top prong being the ground and the second one down the running lights. All the trailer lights stopped working at the same time. With the truck lights on, I think I should have 12V between the 2 but have nothing. The ground between the truck and trailer appears OK. The only other trailer that I have had on the truck lately has the 6 prong next to the 4 prong and it worked fine Any thoughts?

Russ from MN · May 17, 2021

I believe there is a separate fuse for trailer lights, our son has a Ford and that's what happened to his. The truck lights worked fine, but no trailer lights. It wasn't easy to find the fuse!

Janicholson · May 17, 2021

Using a test light, with the trailer unplugged, test from the truck actual ground (not the female terminal on the plug) to each male prong. With running lights on there should be 12v on the brown terminal. With the right turn on the green (on the end away from the ground)should flash. the middle of the three should be left turn. If these work with the truck ground, see if they work with the plug ground. If not that is the issue. if nothing works look for that fuse. Every Uhaul dealer has a plug in tester that has LED indicators to assess the supply side electricity. Jim

Jim.ME · May 17, 2021

Here are pictures of a couple of the flat 4 wire testers that might be similar to what Janicholson mentioned. You can get them for many different plug configurations at parts stores, Walmart, TSC, and many places that have a trailer towing section, even Harbor Freight.

Bill Tattersall · May 17, 2021

I considered the fuse possibility but going through the long list of fuses in the owners manual couldn't seem to find a likely culprit. I will look again. The test light using the plug ground works good on the turn signal prongs but I have nothing on th running light prong.

Jim.ME · May 17, 2021

(quoted from post at 17:45:39 05/17/21) I considered the fuse possibility but going through the long list of fuses in the owners manual couldn't seem to find a likely culprit. I will look again. The test light using the plug ground works good on the turn signal prongs but I have nothing on th running light prong.

Check fuse # 67 in the fuse/relay panel under the hood. I think it may be a 20 amp fuse.

Bill Tattersall · May 17, 2021

#67 it was!! Thanks so much.

In all the years I have been participating in this forum, I never cease to be amazed at the extant of the knowledge this exists here. Long live Yesterdays Tractors.

Sprint 6 · May 18, 2021

Now the next step is to find and fix the short in one of your trailers.

ASEguy · May 18, 2021

If your fuse is good, I would plug in your test light, or have a partner do it, and wiggle test the wires until you find the location where the test light comes on. Good luck.

bc · May 18, 2021

I got pulled over one time for no trailer lights. Went back and wiggled the connector and they came on. Told him I could make the wife lay in the back of the pickup wiggling the wire connector for the rest of the trip. He said I was good to go.

F150 4 Prong Trailer Plug

Bill Tattersall

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Russ from MN

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Janicholson

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Jim.ME

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Bill Tattersall

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Jim.ME

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Bill Tattersall

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Sprint 6

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ASEguy

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bc

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