Power to harness until I plug trailer in

[ReefRaider]

I have power to my 4 pin harness on the towing vehicle, plug trailer into it and then lose it. Trailer lights work fine with other vehicles so that is eliminated. Ground on this vehicle seems fine. It has one of those Modulite converters on vehicle, am thinking that is the problem unless someone here has another theory. Thanks.

 

[Gary H NC]

Re: Power to harness until I plug trailer in

Sounds like a dead short in the trailer wiring.
Are you saying no lights at all work?

Just realized the trailer works with other tow vehicle...(sorry)
I would be suspect of the converter..

 

[Knightgang]

Re: Power to harness until I plug trailer in

Is it blowing fuses when you plug into that vehicle? I have never used those converters, but I would suspect it was at fault. I have to help a neighbor trouble shoot his one night...

 

[ReefRaider]

Re: Power to harness until I plug trailer in

Nope, not blowing fuses. 12v at harness....plug in trailer (leaving enough room to touch prongs with meter)....no voltage. It simply "dies". Disconnect harness, vehicle end has 12v again....still leaning toward this power modulator box http://drawtite.com/modulite1.html I'm not familiar with them, thought others may have had similar issue.

Trailer is not it. Not only does trailer works fine with another vehicle, but have same problem when hooking up another working trailer to this tow vehicle.

 

[Knightgang]

Re: Power to harness until I plug trailer in

Gotta be the converter. Just wire in a new one and be good to go...

 

[boat1010]

Re: Power to harness until I plug trailer in

Just to make sure I would plug in another trailer.. If the same thing happens then pretty much a no brainer. Its the modulator.

 

[cribber]

Re: Power to harness until I plug trailer in

I blew my 4 pin converter once using a trailer with electric breaks which gave the same indications. Good solid 12v with the meter on the open plug, and dropped to 5 when the trailer was connected. New harness and converter should be around $25 - $35. That way you don't have to worry about bad splices.

 

[Bifflefan]

Re: Power to harness until I plug trailer in

I blew my 4 pin converter once using a trailer with electric breaks which gave the same indications.

You learned a lesson there,, Use the right plug for the trailer.

 

[ghamby]

Re: Power to harness until I plug trailer in

Have you metered out all the functions: turn, brake, and running lights without the trailer plugged in?

 

[HappierWet]

Re: Power to harness until I plug trailer in

My converter has a seperate ground. I had a problem with the turn signals but not the running lights and that was it. Also check the plugs ( if it's the plug and go style harness ) for corrosion. A lot of the vehicles I see have voltage at the plug, but no current when we load test and that's the issue. Good Luck

 

[walt-oxie1]

Re: Power to harness until I plug trailer in

If you are getting power to the plug on the tow vehicle (hooking meter or test light to ground on plug) and everything works correctly on it, the trailer could be the issue. The trailer or vehicle could be wired different and cause it to not work. Remember, white is ground, green is right, yellow is left and brown is for running lights. It should be the same on the trailer and tow vehicle.

 

[CharlieB]

Re: Power to harness until I plug trailer in

Since BOTH trailers work fine on another vehicle and BOTH trailers fail once plugged into the converter box and the voltage fails once either trailer is plugged into the converter box then it should be clear that the problem is a poor connection in the micro-circuit within the converter box.

The box must be replaced.

 

[TerryMSU]

Re: Power to harness until I plug trailer in

Since BOTH trailers work fine on another vehicle and BOTH trailers fail once plugged into the converter box and the voltage fails once either trailer is plugged into the converter box then it should be clear that the problem is a poor connection in the micro-circuit within the converter box.

The box must be replaced.

Bsically true, however it is possible that it may be an electrical connection to the wires from the box, especially if they are not factory connections. This is especially true of the ground as it appears that you are losing all function. Look at the crimps on the box. By the way, using dielectric grease on these crimps will go a long way toward preventing a re-occurance.

TerryMSU

 

[CharlieB]

Re: Power to harness until I plug trailer in

Right Terry, he MUST verify the original installation connections are CLEAN, bright and tight, it could save him the cost of another box.

IF I would have checked that I might still be driving my 81 Datsun KC 4 X 4 , that got a LOT better mileage, instead of my 03 S10 4 X 4.

 

[Splat]

Re: Power to harness until I plug trailer in

Call me crazy, but I'm still leaning towards a ground issue on the vehicle. Especially if your loosing both sides of the circuit.

It could be the converter, but I would start with the ground running to it.

Its also possible that the converter box is a powered one, and the constant power wire is corroded or otherwise fubar

Bill

 

[benmcclure]

Re: Power to harness until I plug trailer in

I had an issue very similar to this on my jeep Grand Cherokee. It has a 7 pin outlet on the back of the jeep.

I would see voltage until I put a load on it then the voltage would drop way below 12 volts(close to 3-4 volts) and it wouldn't light up most incandescent lights.

It ended up that under the jeep the harness that plugs into the connector was loose and making a very unstable connection.

Its probably not the cause, but It took me quite a while to find this one as I was blaming the trailer, but all the tests I could do on it (powering each individual light) were coming out fine.