More electrical help for the electric idiot

Ok so the boat/ trailer demons have really hit me hard lately. I’m starting to think someone put a curse on me. Solved one problem yesterday and in the process created another one. Dropped the boat off at a lake and took the trailer to a welder to fix an issue. After getting the boat loaded back up my wife noticed that my trailer lights we not working. None of them. Stoped and checked the plug-in, that was all good. My first thought was that during the welding the trailer frame got hot and possibly melted part of the trailer harness that runs through the trailer frame. Before I jumped Into that I decided I better check the truck side. I found the 4 pin plug-in tester I have and determined I had no power to the truck connecter, Neither the 4 pin or the bigger round plug-in. After looking at the manual and doing some research online. I found a blown fuse in the box under the hood. Once I replaced the fuse the tester shows I have running lights, but no turn signals. Doing some more research I think it may be relay 37 and 38. These are a black 4 prong relay. Is there a way to test these with a multi meter before I buy them. I’m not sure if these are even available at a auto parts store. See pictures for ref. the replays are 37,38 just to the right of the pen point

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More info on the truck would be good. We have had some blown fuses when trailers had issues and some were just fuses and some needed a relay and if I remember right a relay relocation.

I’m not real sure that if I get the truck side working correctly that I may not still have a problem on the trailer side which caused the blown fuse on the truck in the first place. I really hope I don’t need to start pulling the wiring on the trailer. That will be a real headache

Sorry it’s a 2012 ford f150. I guess that info would help

Talked to one of my techs and he said replace the relays, most part stores should have them and not to expensive. The real issue is the trailer may have a short to have blown the fuse and relays. So replace the relays and have a close look at the trailer or take it in for someone else to have a look. I’m happy to have someone help if you want to make a run down here.

Did they leave the trailer connected to the truck when they were welding it? If so that is a terrible idea.

CaptainMusky wrote:

Did they leave the trailer connected to the truck when they were welding it? If so that is a terrible idea.

Hopefully not! You can test the relay. Pins 3-5 are a set of normally open contacts if you use your meter set to continuity or ohms you should see an open circuit. Pins 1-2 are the coil that closes the contacts when 12vdc is supplied. If you test across these pins while in ohms you should see some resistance. If you apply 12vdc from a battery to pins 1-2 it should close the contacts 3-5. Usually pickups have trailer fuses for running lights and turn signals I would check for both. If fuses were blown after you connected the trailer for first time I would believe that the trailer wiring was melted and is shorting to ground. So a captain asked was the trailer connected while welding if so you may have plenty of electrical problems now if not I would look at the wiring where the welding was done. I have included the pinout of the relay.

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CaptainMusky wrote:

Did they leave the trailer connected to the truck when they were welding it? If so that is a terrible idea.

The welder did leave it all hooked up to the Truck. I did ask him after I have the light issue if his grounding the Welder to the trailer could have caused a issue. He said he did not think so as he grounded the welder to the far back of the trailer. I did not even give the ground a thought or the heat of the trailer frame. Probably something both him and I should maybe have thought of, but didn’t. I don’t blame the welder. I brought him a trailer to weld and he welded it. I guess I’ll just need to start with the truck side and once get that working plug in the trailer and see if it works and if it happens again, If so then I’ll start chasing the wire harness issue to find the cause of the problem. I’m starting to think the fishing gods don’t want me to make this fall Canada trip. What started as a few preventive issues has turned into a real cluster F

Very bad idea having the trailer grounded while attached to the truck. The welder should know better. I’m guessing that blew the relays. And hope that’s the only ones it affected.

supercat wrote:

Usually pickups have trailer fuses for running lights and turn signals I would check for both.

The Truck turn signal are working fine. Just not the Trailer. I have not actually plugged the trailer in to check what is working and what is not. I’ve simply been relying on the test Plug in. I have checked both the 4 pin and the round plug-in. Test light shows only the running lights are receiving power on both.

FYI if you have to weld something electrical and can not remove it you always attach the ground from welder closes to the area you are welding. I’m not saying it caused your problem but I have seen bad things happen when welding on items that have electrical components.

fishthumper wrote:

<div class=”d4p-bbt-quote-title”>supercat wrote:</div>
Usually pickups have trailer fuses for running lights and turn signals I would check for both.

The Truck turn signal are working fine. Just not the Trailer. I have not actually plugged the trailer in to check what is working and what is not. I’ve simply been relying on the test Plug in. I have checked both the 4 pin and the round plug-in. Test light shows only the running lights are receiving power on both.

Correct the truck signal fuses and trailer fuses are different. You should have at least 2 if not more fuses just labeled for trailer lights only.

John Rasmussen wrote:

Talked to one of my techs and he said replace the relays, most part stores should have them and not to expensive.

I think I’ll start with this. Worth a shot. Hopefully I can find a few on my way home. I did purchase a extra fuse of the one I replaced yesterday that got the running lights working ( #67 )

According to what I found on the internet fuse #73 is for the stop turn lights power I would check this fuse.

supercat wrote:

Correct the truck signal fuses and trailer fuses are different. You should have at least 2 if not more fuses just labeled for trailer lights only.

In the manual I could not find any Fuse in the box located under the Dash for the Trailer connection. In the manual it shows Just one Fuse and 2 relays in the box in the engine area

Does it look like this
https://www.startmycar.com/us/ford/f-150/info/fusebox/2012#anchorfusebox1

This should be located under the hood

Supercat. Thanks for the photo. I missed #73. I will check that one as soon as I get a chance.

fishthumper wrote:

Supercat. Thanks for the photo. I missed #73. I will check that one as soon as I get a chance.

That photo is actually interactive just hold your mouse over the item in questions and it will tell you what it is for good luck.

supercat wrote:

FYI if you have to weld something electrical and can not remove it you always attach the ground from welder closes to the area you are welding. I’m not saying it caused your problem but I have seen bad things happen when welding on items that have electrical components.

The welder did connect the ground close to the area of the weld. He was welding near the tire area and he grounded to the trailer frame a few feet back from there. Right at the end of the Trailer frame.

The welder hopefully caused the issues and with some new relays your back up and running. Otherwise check the trailer carefully.

John Rasmussen wrote:

The welder hopefully caused the issues and with some new relays your back up and running. Otherwise check the trailer carefully.

Ya. Hard to believe but I actually hope its on the Truck side. Easier for me to try and figure out and fix. The thought of digging into that Trailer wiring is Not good.

The good news is that we are not using my Truck to pull the boat to Canada. So I’m sure the other guys truck does not have a problem. The bad news is that if there is a short in the trailer wiring, it may cause a problem with his truck

I keep a set of these in the truck in case of boat trailer light issues. (These magnetic ones or clamp on style) Cheap insurance! Good Luck on your fix.

-J.

http://www.amazon.com/MaxxHaul-80778-Magnetic-Trailer-Approved/dp/B078GNDQQH/ref=sr_1_10?crid=1WN96VYKO4DZ0&keywords=trailer%2Blights%2Band%2Bwiring%2Bkit&qid=1692111250&sprefix=trailer%2Blights%2Caps%2C178&sr=8-10&th=1

That’s a pretty good idea Jon.

John Rasmussen wrote:

That’s a pretty good idea Jon.

Yes it is. I may have to purchase that. It won’t do me any good unless I get the truck side figure out, But may become necessary if there is a trailer short and I cant get it figured out in time for our trip.

Swap the relay with another one that’s working. Like the turn signals. I have a 2010 f150, there’s several of those relays in there.

Plunker wrote:

Swap the relay with another one that’s working. Like the turn signals. I have a 2010 f150, there’s several of those relays in there.

This is correct and one way to trouble shoot, would not be the worst idea to have a spare relay either.

I use to have a ford expedition, pretty sure it was very similar wiring system and I would blow two fuses. It was a bad ground wire I finally repaired correctly.

My neighbor shorted his plug out and we tried to fix. It was one of those big ones at the bottom. 73? 78? It was not visually obvious at all.