Electrical outlet, rear bumper.

[taildragger03]

Have a question concerning the electrical outlet on the rear bumper. I am trying to use this for the lights on my M101A1. Finding out that I have a bleed over from several of the circuits and is affecting the operation of the lights. After testing the plug, I found that I have 4 grounds (BDEJ) are connected as grounds. I went through appendix F and could not find anything other than on page F-13 that says "TRLR ELEC CONN". Is there a schematic that covers this plug? Need to find the correct ground and isolate it.

Thanks

 

[Barrman]

If you look real close at the rubber on the plug, you will see little letters next to the pins. Here is what the pins do:

A=wire 24
B=wire 22/460
C= wire 24
D=wire 90 ground
E=wire 21
F=wire 23
J=wire 22/461

Here is a listing of what the wire numbers mean:

M-SERIES VEHICLES CIRCUIT NUMBERS

 

[taildragger03]

Thanks Barrman for lining me out on that!

Does it make sense that the four pins I am using (BDEJ) are connected
through ground? D-pin is listed as the primary ground, by using the buzzer on my volt meter, I get sound at B-E-J pins
as well. Each circuit works correctly, till I hook up the trailer and get multiple patterns of lights flashing.
Any ideas? Or just keep testing each circuit.

 

[doghead]

Maybe the trailers cord, is connected wrong? Have you confirmed all wire numbers match, on the trailer(at all of it's connections)?

Also, remove and clean both bolts on both taillights.(they both are used for separate circuit grounds).

 

[Barrman]

No it doesn't make sense. However, all true design military vehicles such as the M35, M37, etc... Have wierd things happen if a ground is not good. Take the 4 bulb bucket tail lights on your 101. If you unplug all but one light power wire. Then undo the ground bolts at the back. Chances are a light that isn't even plugged in will light up when you apply power to the one wire left hooked up. I know it doesn't make sense. I also know I have had this happen when making wiring harnesses for my M715 and my Gasser M35. Weird things happen to MV's when the ground isn't right. Un bolt your lights, clean the bolts and bolt them back up since that is your ground. Do you have the plastic light buckets? Only one of those bolts is the ground and it can come loose from the grounding strap inside the bucket. Start there.

If your plug on the bumper test out like the listing I posted. Then you probably do have a problem on the trailer. Un plug the lights and then pull the cover off the pig tail to trailer connections. Unplug the pig tail. Then using your ohm meter, verify that each wire at the front of the trailer actually goes to where it is supposed to on the back. Plug things at the light buckets back up as you test each wire. Now, plug the pig tail into the truck with it still not plugged into the trailer. Test everything for power at the proper wire number. If every thing checks out, start connecting the pig tail back to the trailer one wire at a time. Test each one for working lights before you move on. If everything works great until the last wire gets plugged in and then everything goes stupid again. Unbolt the light buckets from the trailer, remove the bent metal hanger for the lights, clean everything and put it back together with star washers on the 3/8" bolt holding the buckets to the holders.

 

[taildragger03]

Having checked out the wiring on the plug, B is supposed to be Right turn/stop and the J pin Left turn/stop. On my 1028 it is reversed.
I am wondering about multiple grounds though. I do use the trailer with my civy truck and everything is peachy.
Since I use a ground through the truck and the 1028-trailer would use the mounts for the lights on the trailer, there could be a problem there.

 

[amphi]

I am wondering about multiple grounds though.

Pins BEJ are directly connected to light bulbs on both the truck and trailer. These bulbs are grounded on the other end.

Since you are using a continuity tester that buzzes when it detects a ground, you are probably reading thru the bulbs indicating a false ground. Use an ohmmeter on a low scale and compare the reading to the real ground at pin D.

Turn on the lights, hit the brake and look for voltage on these pins.

 

[KsM715]

Sometimes visual helps. It help me when I printed these off and had them right beside me when I was checking out the wiring on my truck and trailer plugs

Edit: in the first pic you can disreguard the vehicle interconnecting cord. But the plug on the right is how the connector of your truck should be wired. ( I think not real sure about cucv's but they should all be the same)

 

[taildragger03]

That is something I needed! A schematic to show me how things lay out. Still working on this one fella's. Going to get after it again tomorrow. I will get back to you all as to what I find.

 

[taildragger03]

So after playing cat and mouse between the CUCV and trailer, it turns out that the problem was with the ground on the trailer. The interesting thing is that the lights worked with the civy truck yesterday but with the CUCV, the trailer had other plans.