7 Wire Trailer Connector Question!

ss502gmc · May 10, 2009

I need my 12v trailer wire to work and it doesnt and the fuse IS good and cant find corroded or broken wires Please HELP!!!!

Mike2500HD · May 10, 2009

I need my 12v trailer wire to work and it doesnt and the fuse IS good and cant find corroded or broken wires Please HELP!!!!

First thing always is to spray with WD-40 and work the plug in and out a few times. Corrosion you cant even see can keep it from making contact. Sometimes you need to move the trailer around on the ball to get a proper ground also.. Good luck.

brims · May 10, 2009

I need my 12v trailer wire to work and it doesnt and the fuse IS good and cant find corroded or broken wires Please HELP!!!!

First thing always is to spray with WD-40 and work the plug in and out a few times. Corrosion you cant even see can keep it from making contact. Sometimes you need to move the trailer around on the ball to get a proper ground also.. Good luck.

Thought there was a ground wire in the 7 way connector, the center pin if I remember correctly.

I stand corrected, the white pin is ground. http://www.etrailer.com/faq_wiring.aspx

Get a mutlimeter, you can get one at Harbor Freight for $3 if you don't want to spend much, and test between ground and the 12v. It should also have the diagram on the 7 way outlet cover.

bill190 · May 10, 2009

These wires can usually be traced "by looking" as opposed to needing a wiring diagram (as would be the case with hidden and inaccessible wires).

If you don't get voltage at the connector, just follow the wire up all the way under the vehicle to the front and inspect it all along its run. Feel back behind the harness (where you can't see) with your hand for cuts in the cable. Check every connector along the way. Unplug any connectors along the way and test for voltage with your multimeter.

RJG183SA · May 10, 2009

When you say "the fuse is good", are you refering to the fuse in the underhood power dist. ctr.?

I know in my case (2003 HD) there was a dummy fuse in place. I had to insert a fuse (30 or 40 amp not sure) to get power to the terminal that provides juice to the trailer batt.

sonjaab · May 10, 2009

RJ is correct !

03 and up GM put a dummy fuse in stud #1. Also note

the position of the 12v trailer batt. power pin is different.

Use a test light to verify !

I went thru this when I tried to use my 01s factory supplied trailer

plug leads on my 04......................

brims · May 10, 2009

I've heard of them using dummy fuses a couple times now that you mention it. What is wrong with GM. Why didn't they either leave the spot blank or put a real fuse in, doesn't make sense to me.

sonjaab · May 11, 2009

Why? Simple.....DE-contenting !!!!!!!!!!!!

03 was a fine year and GM got CHEAP..............No more fuse in either stud1 or

stud2, no more free trailer 7 to 4 cord, no more trailer brake underdash cord,

no more floor flood lights, no more bang strip on each side of the bed, no more power lumbar, no more underhood light, one less power outlet etc............

There are a few other goodies GM took away....Who knows the ones I missed?

ss502gmc · May 11, 2009

Well i have a real fuse and i checked with a test light and i got power on the stud #1 and i followed the wires from the connector up to the cab so far and so far no broken wires and there is absolutely zero corrosion anywhere. So not sure what to do next. Im at the point im about to run a wire right from the battery to the plug with an inline fuse!!! Im getting frustrated but oh well i guess Theoretically that wire should go from that stud #1 right down to the back right?? I would think so.

bill190 · May 11, 2009

There is no way to tell where the wires go (if you can't follow them) without a factory electrical manual.

How many amps is that fuse and where is the fuse located? (Inside vehicle or under hood?)

The +12 volts to a trailer should be around 25 or 30 amps.

If it is a low amperage fuse INSIDE the vehicle, it may go to a relay under the hood and the contacts of that relay would be on another high amperage fuse.

And if there is a fuse/relay under the hood, then the wiring should go from that, under the vehicle, and to the trailer plug. This would be exposed and you could follow that wiring.

The wiring from a relay under the hood to a fuse for the relay inside the vehicle would be impossible to follow because it would be intertwined in a mass of other wires.

But I am just guessing without a wiring diagram to look at.

sonjaab · May 11, 2009

[quote ....But I am just guessing without a wiring diagram to look at.

Here ya go:

This link has full info. and pics:

http://www.marksrv.com/wiring.htm

The trailer 12v will be either lug #4 or the center lug depending on year.

Use test light to verify.

sonjaab · May 11, 2009

BRIMS..............If you haven't already found out...........

Wait till you go to hook up both the trailer power lug in your rear plug

AND your aux. trailer brake controller in your GMT-900 !!!!!!!!!!!

Neither wire is hooked up and just left loose under the hood hidden near

the underhood fuse center for YOU to hook up. Plus NO more plug n play

for your trailer brake controller either like the gmt-800s.

There is a thread with instructions and pics around here somewhere!

bill190 · May 11, 2009

THIS is a factory Electrical Manual for a vehicle, but wrong year (over 600 pages)...

http://www.gmupfitter.com/publicat/2008_BB...FST_Elec_D3.pdf

brims · May 11, 2009

Why? Simple.....DE-contenting !!!!!!!!!!!!

03 was a fine year and GM got CHEAP..............No more fuse in either stud1 or

stud2, no more free trailer 7 to 4 cord, no more trailer brake underdash cord,

no more floor flood lights, no more bang strip on each side of the bed, no more power lumbar, no more underhood light, one less power outlet etc............

There are a few other goodies GM took away....Who knows the ones I missed?

Ya, but putting in a dummy fuse can't cost much less than a real fuse, so why put anything in the hole. I understanding they were, and still are, trying to cut corners.

BRIMS..............If you haven't already found out...........
Wait till you go to hook up both the trailer power lug in your rear plug

AND your aux. trailer brake controller in your GMT-900 !!!!!!!!!!!

Neither wire is hooked up and just left loose under the hood hidden near

the underhood fuse center for YOU to hook up. Plus NO more plug n play

for your trailer brake controller either like the gmt-800s.

There is a thread with instructions and pics around here somewhere!

Ya that whole mess is just stupid. And on top of them not connecting you have to cross the wires. Why was it so difficult for them to have the studs swapped around? I have looked at that many times and am just dumbfounded.