Explorer trailer wiring problem, help, please!

[jtexas]

I thought I knew about trailer wiring but this problem has me so confused.......

It's a 98 Explorer Sport, 4-flat trailer harness, factory trailer wiring, with an adaptor plugged in under the drivers side bumper. It's worked fine for years.

Now I don't have brake/turn on the right side.

Fuses are fine.

Voltmeter shows plenty voltage (12.5+) at both fixtures with the brake pedal depressed. Left side lights up, right side doesn't.

Here's the part I don't understand...using jumper wires to connect a lamp directly to the vehicle connector (trailer disconnected), brake pedal depressed, the yellow wire lights it up, but the green does not, even though both wires test good for voltage.

Any ideas?

I also noticed that the running lights work with the ground disconnected from the trailer frame (vehicle not hitched), but turn off when the brake pedal is depressed -- I assume they're grounding through the brake filament -- I'm think that's normal...can somebody confirm that for me? thanks.

 

[bitterboater]

Re: Explorer trailer wiring problem, help, please!

Is it the tow vehicle that is having problems, or the trailer that is having problems?
If it is the truck. I have had a similar issue, the solution was to remove the trailer adapter. It had shorted out, causing the lights to not work.
If its the trailer, you may well have a bad plug, they do go bad. recently had this as well with my suburban. I removed a light that had shorted out and was causing a problem on the trailer itself, however the plug at the truck was shorted out as well and not functioning properly.

These are the things that make us pull out what little hair we have left.

 

[jtexas]

Re: Explorer trailer wiring problem, help, please!

I'm convinced the trailer wiring is good, even ran dedicated grounds back to the fixtures.

going to bypass the adapter plug for some tests....

 

[gonefishie]

Re: Explorer trailer wiring problem, help, please!

Just yesterday, I figured out my buddy running lights problem on his trailer. Everything was working fine then all of a sudden no running lights, all others were fine. He has nothing for testing with. I improvised with his spare battery and a couple of wires. By hooking the battery to the trailer harness I proved that all the lights on the trailer work properly. Using the jumper wires, I determined the brown wire on the truck harness puts out nothing. His truck is a newer Lincoln Navigator. We had to pulled out the user manual to find the fuse panel and figured out which fuse is which. Turned out the fuse labeled in the manual as back up/park lamp was blown. It's neat that Ford uses seperate fuse for each of the circuit but it's kinda confusing. There's more than one circuit that has to do with park but nothing says running light. I don't know if your Explorer is set up the same way but worth checking out.

Your issues sound like there's a problem with the green wire circuit and/or ground on the trailer.

 

[EddiePetty]

Re: Explorer trailer wiring problem, help, please!

...I, too, would recommend testing/eliminating the trailer wiring by connecting a battery to the trailer leads.
Before you proceed any futher, please ensure that all the lights on the tow vehicle are functioning correctly with the trailer disconnected. I once discovered a 1157 bulb that had blown one of its filaments and had welded to the other filament.....drove me nuts until I checked the tow vrhicle separately.

 

[jtexas]

Re: Explorer trailer wiring problem, help, please!

ok, I took the factory plug out the circuit...just like bitterboater said...just replaced it with 4 bullet connectors. Now I have brakes and turn signals, both sides.

unfortunately, now the brown wire has no voltage, where it comes out the vehicle wiring harness inside the taillight lens.

you're right, the fuse is described as park lamps/trailer...I blew that one earlier & replaced it, it's still good. there's another parking lamp fuse under the hood, it controls the vehicle taillights, it's good, too.

Don't know what I did to cause that. I'm assuming, since the trailer wiring is on a separate fuse, it would be a mistake to tap into the truck taillight circuit.

I have a mostly useless Haynes manual here, but it does have complete wiring diagrams, maybe I'll find a clue........

 

[gonefishie]

Re: Explorer trailer wiring problem, help, please!

So your brown wire is tapped into the tailights?

 

[burp]

Re: Explorer trailer wiring problem, help, please!

Ford Explorers have a 20 amp fuse in the under hood fuse box which is used only to power the trailer marker lights.

 

[Silvertip]

Re: Explorer trailer wiring problem, help, please!

STOP shotgunning and do some troubleshooting. Verify the truck is ok with either a test light or voltmeter. If its ok the problem is the trailer. Again, it was suggested using a battery or a battery charger to test the trailer lights. COnnect ground on the battery or charger to the white wire. Touch the positive to each of the other three. It either works or it doesn't. And by the way, circuits do not ground through a bulb. One side of the bulb IS ground or that bulb won't light unless it gets a ground through some other circuit which is also NOT normal.

 

[jtexas]

Re: Explorer trailer wiring problem, help, please!

no, gonfishie, they aren't, just a bit of momentary confusion on my part.

anyways everything works now. can't explain that last running light failure, must of been "operator error"...

btw, burp, the inside fuse box on my '98 explorer has two 7.5 amp fuses for stop/turn (one each side), and a 15-amp for trailer "parking" lights. plus a 15-amp in the power distribution box under the hood for vehicle parking lights (includes the tail lights).

thanks for the comments, silvertip, I used a test lamp to confirm the problem with the vehicle "adapter". The 2-filament lamps in my trailer lights are tied together on the ground side (these are the round "bayonet" base bulbs, where both filaments are grounded through the base, not the 3157's which are different). When the brakes are off on my car, the stop circuit measures approx 0 volts (not open circuit) -- so it turns out, the running lights are grounding through the brake light filament (ground wire not hooked up and trailer not hitched). They aren't as bright as when the ground is hooked up, but they do illuminate. Sure hope that doesn't indicate a problem of some sort in the truck -- sounds like it'd be an expensive fix.

Thanks to all who contributed!