vehicle fuses

[maxwell_smart007]

I tested a number of fuses to find out why my trailer lights weren't working - discovered that they're still showing no power after replacement.

My test light will not light up when you test them. I assume there's some sort of relay or something like that - but the word 'relay' is the extent of my knowledge on the subject!

Any ideas?

Andrew

 

[JohnLifer]

Check and RECHECK your ground.....
my trailer lights quit, one was damaged so I replaced recently.
still not working. Then, got one working and finally when I added a better ground, both worked. Is there power at the outlet on your car/truck? if so, then ground!

 

[Davidh14]

My hitch gets pretty rusty after not using it awhile. After pulling a trailer for a bit it will rub the rust off allowing for a good ground.

 

[leehljp]

You didn't change vehicles by any chance, did you?

Otherwise, grounding, or a pinched/cut wire somewhere.

 

[bobleibo]

Andrew
The grounding comments already made are probably correct. Two things I've found that may contribute
- often the ball and hitch is used to make the grounding circuit from the trailer to the tow vehicle and is not always the best one. I've always run a dedicated grounding wire thru the wiring harness to both the trailer and tow vehicle frame.
- check to make sure your grounding wires are on bare metal. Sometimes, they connect to semi-scraped painted body parts that don't do such a great job. Connecting to your battery neg post if possible is the best.
Cheers
Bob

 

[maxwell_smart007]

No power to the harness plug either....so problem on truck end.

Why would five fuses have no power but not be burned out?

 

[Mr Vic]

No power to the harness plug either....so problem on truck end.

Why would five fuses have no power but not be burned out?

Gremlins!!!

Check for power to either side of the fuse. If there's power on one side and not the other the fuse could possibly be blown but not visible.

I understand that if you leave out a beer and peanuts it will make the Gremlins happy and they will move on. But, don't get them wet or feed after midnight.

 

[maxwell_smart007]

Yep, I checked both sides - discovered one that was culprit this way, but the majority are still just dead...replaced them anyway, to no avail...

Wow, this is frustrating!

 

[jttheclockman]

Where are you testing fuses??? Do you have the vehicle on when testing?? If you have a continuity tester, pull the fuse out and test it that way. That will tell you if the fuse is good or not. Sure fire way. If fuse is good and no power then you have to look elsewhere.

Then the next questions will be what make and year is the vehicle?? Did they ever work?? Is this a new harness???

 

[maxwell_smart007]

I'm testing the fuses in the panel, with a test light - which I checked before starting. I've methodically tested every fuse in the panel and found the dead ones, and replaced them twice, with no changes. There must be a relay that powers these fuses in the panel, I'd guess, as I can't think of any reason why only these fuses would be powerless....

 

[jttheclockman]

I'm testing the fuses in the panel, with a test light - which I checked before starting. I've methodically tested every fuse in the panel and found the dead ones, and replaced them twice, with no changes. There must be a relay that powers these fuses in the panel, I'd guess, as I can't think of any reason why only these fuses would be powerless....

Turn the vehicle on and test. Not all fuses are hot just sitting there. Why are there dead fuses?? Did something short out??? If replacing are they blowing right out again?? Need to test the fuse out of the panel. Does your vehicle have a tow switch?? Turn it on.

 

[maxwell_smart007]

yes, I've tested in auxiliary, and in full-running mode. No symptoms short of a lack of trailer lights - fuses test good (tested ohms with multimeter).

 

[jttheclockman]

Is this a new harness?? Did the lights work before??? You may have to continuity test the harness to see if all wires are in good order. You have to start somewhere and that somewhere will probably at the truck connection before you hook the harness into it. See if you have power to all wires as needed. Turn signals, brake signals and such. If so then plug harness in and again test. If all Ok then plug into trailer and if still does not work then you will need to look at the ground situation as was mentioned.

 

[jttheclockman]

This may be of help to help explain what I was saying.

http://www.youtube.com/watch?v=C4IgUPB7als

 

[maxwell_smart007]

Well, I ran a new ground, and no difference. The fuse panel is still dead on those fuses - nothing seems to get me any life on them...

Odd, but I guess I'm stuck bringing it to the dealer.

Thanks for the help!

 

[Terredax]

It will depend on the year and make of the truck.

It sounds like there is no power at the fuse panel. There is a hot side and a ground side on the fuse. Be sure to check both sides.

On newer vehicles, there is a fuse block under the hood with fuses and relays. Check those first using a diagram to identify the proper components.
If you show hot there, replace the component.

Newer vehicles also have a soy based coating on the wires, which mice love. I doubt that would be the issue, since it's isolated to the trailer wiring only.

If there is power at the fuse panel inside the vehicle, and no power at the trailer plug, it is a ground issue or broken wire. The harness is usually grounded near the rear of the vehicle. Find that, remove it and clean the terminal and the mounting connection to bare metal. Reassemble and if the lights work, apply silicone over the connection.

Sorry, that is about all I can suggest without knowing the make, model and year.
Maybe it will be beneficial.

 

[maxwell_smart007]

It will depend on the year and make of the truck.

It sounds like there is no power at the fuse panel. There is a hot side and a ground side on the fuse. Be sure to check both sides.

On newer vehicles, there is a fuse block under the hood with fuses and relays. Check those first using a diagram to identify the proper components.
If you show hot there, replace the component.

Newer vehicles also have a soy based coating on the wires, which mice love. I doubt that would be the issue, since it's isolated to the trailer wiring only.

If there is power at the fuse panel inside the vehicle, and no power at the trailer plug, it is a ground issue or broken wire. The harness is usually grounded near the rear of the vehicle. Find that, remove it and clean the terminal and the mounting connection to bare metal. Reassemble and if the lights work, apply silicone over the connection.

Sorry, that is about all I can suggest without knowing the make, model and year.
Maybe it will be beneficial.

Thanks John - I ran a new ground, but no fix. It's a 2005 fx4 f150...no power to the fuses on either side. Only 4x4 and daytime running lights relays under the hood in that fuse panel...

 

[Terredax]

Fords... that's all I will say.:wink:

On that year, I believe they had a windshield leaking problem and caused a GEM module failure. But, that doesn't usually affect the trailer wiring.

I also believe there are two fuse panels, one on the end of the dash on drivers side, and one in the passenger side kick panel. Have you checked both of those for associated fuses/relays?

Also, the power distribution block under the hood, I believe some of those fuses/relays are trailer lighting. If there is no power at the interior fuse panels, the problem is before those panels, which leads me to think it may be the PDB. The owners manual should list the fuse and relay functions.

Oh yeah, we have a ford. Have been dumping way too much money in it lately.:redface:

 

[JohnLifer]

Do you have brake lights on the truck? and tail lights with your headlights on? and turn signals?
If so, it is not fuse. Same circuits powers all of those and the plug for trailer lights. Nothing separate... Just sayin.
check wiring from the plug.

 

[Terredax]

OK, I asked a friend that's a Ford guy.
He said it isn't a GEM anymore, it's a CJB (pass side kick panel) and not "smart".
He said there is a built in relay in the CJB that controls the trailer lights and is a common problem. It has to be removed and replaced if it's bad and it's simple to test. Replacing it is a little involved or the CJB can be replaced, with that option being more costly. About $25 to replace it.

There is also a #9 and #38 fuses that seem to blow often.

 

[truckfixr]

Fuses 36 and 42 in the CJB supply power to the trailer turn signals on an 05 F150. If your turn signals on the truck function normally, you will have power to the fuses. If you haven't solved your problem by tomorrow, give me a call. I'll be happy to try to help you figure out the root cause of your problem. You can reach me at (830)665-4461. Just ask for Chuck Pruett. I'll be here at work (Ford Dealership) from 8am-6pm CST.

 

[truckfixr]

Do you have brake lights on the truck? and tail lights with your headlights on? and turn signals?
If so, it is not fuse. Same circuits powers all of those and the plug for trailer lights. Nothing separate... Just sayin.
check wiring from the plug.

Actually, on this model the trailer turn/stop circuits do have their own fuses.

 

[bobleibo]

Andrew
It looks like you have some real expert help headed your way. When you finally figure it out, please post the results. I've often run across things like this and the problem turns out to be a very simple fix or something I never even thought of. Either way, I learn something new. This one really has me curious because auto electric has always been my weak spot.
Good luck
Bob

 

[maxwell_smart007]

I very much appreciate all the help! It's been insanely hectic around here for two days, but I'm really hoping to make use of the help that's been so generously proffered asap!

I'm very much thankful of all the help!