Test Trailer wiring harness without trailer.

[erikgil]

OK, here's a unique situation. I've gotten my rusted hitch removed (prev. one fell off towing a stump - glad it happened in the woods and not my trailer with a load). Put a newer hitch on so I can physically tow now. But the PO had wired in a trrailer wiring harness and tucked it up under the body.

How do I test it without my trailer? I have a multi meter and a resistance tester (if that's what it's called). The trailer is actually a few hours away from the truck and as luck would have it the person I loaned it to let their dog at it and it ate my all new trailer wiring. He has new wires for it so I'll repair that when I get there.

So the basic question is, how do I test to see if the harness on my truck is in working order? Have no trailer handy to test.

I friggin hate dealing with trailer wiring. It's either the truck harness or the trailer wiring. or both. grrr.

 

[Kynot62]

You can use your multimeter or just a simple test light. Depends on how you wired it. Each circuit will still show voltage without the trailer attached ie turn on a blinker and that junction in the plug will show voltage on your meter.

And dont forget you may need a converter if you run combined stop/turn signals/running lights on the trailer. Our wagons have seperate circuits for the running lights so to simplify things put the converter in. Cheap in the trailer wiring section of the auto parts store.

Tony

 

[John McVicker]

This is very easy & straightforward. You can us a mulitmeter or a test light. I prefer a test light.

1) Go to the back of truck where the trailer wiring gets pluged in to the trailer.

2) Conect the test light clip to a known good ground. Be certain of this, or you will be chasing non-existent problems.

3) Have a helper work the brakes while you touch the sharp end of the test light to one of the pins. Test light will work in conjunction with the operation of the brakes. You will need to touch all pins in order to find out which is the brakes.

4) Do the exact same thing for all other functions, ie turn signals, running lights etc.

If nothing lights up, do the same test from the pigtail upstream until you determine where you have a bad connection.

It's really pretty easy.

 

[erikgil]

OK thanks. Good idea on the ground. I've already had that fun on another project so the reminder helps.

I'm going from muddy, rainy, foggy, clod and damp memory of a few winter weeks ago in the raid. Lots of the 4-wire and the 4-wire plug underneath. I assume if it needed a converter I might not have seen it. Don't recall seeing it.

Is the converter necessary?

 

[Tinker]

Unless your trailer has separate brake & turn light filaments, you need a converter. Put the flashers on & stand behind your truck: the amber lights flash. Have someone step on the brakes (may need the ignition on): the red lights come on. They're separate on Japanese & European vehicles, but combined on US ones. Trailers normally use US tail lights with combined brake & turn signals.

If your trailer is normal US there needs to be a converter that takes the brake light & each turn signal & combines them, side-to-side. They're easy to install as they're labeled clearly - they go on the towing vehicle.

And I'm with you - seems like most of the time I spend on trailers is the wiring.

 

[KLF]

You're making this too hard.

Four-Way Trailer Light Tester

These things are really handy, I keep one in the back with my hitch insert. I think I bought mine at WalMart for about the same price.

 

[erikgil]

You're making this too hard.

Four-Way Trailer Light Tester

These things are really handy, I keep one in the back with my hitch insert. I think I bought mine at WalMart for about the same price.

Gonna buy it either way. Damn shipping is more than the part. like 13 total. oh well, it's worth it.

Look to me like this only test the actual trailers wiring and not the truck wiring, right? My goal in this thread is to test the truck trailer harnes, not the trialer, though I need to do that too.

Appreciate the lead to this tester, but please clarify my Q above.

 

[77TLCFJ40]

I tests the tow vehicle - not the trailer.

 

[ntsqd]

Suggestion on the trailer's pigtail or jumper; once you get it to where you can work on it, put a socket on/in the tongue. Then the pigtail/jumper plugs into the trailer too. On the Cheep Utility Trailer MISF & I used a 7 pin socket on the trailer. The pigtails or jumpers can then be made to have what ever the tow rig has for a trailer lights socket. Our rule is that if you borrow the trailer and there isn't a jumper that works with your tow rig then the price of borrowing the trailer is to make such a jumper and leave it in the tongue box when you return the trailer. Should anyone cut and splice an existing jumper I'll change the tongue box combination so that they can't borrow it w/o asking for the new combo (coupler & safety chains live in there too).

There's a thread here where those converters are talked about. Even the spendy ones don't seem to last very long. The best are those that need a battery hot in addition to the light circuit inputs.