No power to dimmer switch
 

I recently purchased a Military 1975 Dodge W200 that was converted to a 12 volt system and a 318 was installed replacing the original diesel motor. I am having trouble trying to figure out why the headlights will not come on. All other lights function as they should. I replaced the dimmer and headlight switch. As far as I can tell there is no power getting to the dimmer switch. What do I look for next? Thanks

Other than fuses check the wires in and around the lighting system. Also check the bulkhead connector on the firewall. This is prone to getting wet and the connectors rot out.

If I understand correctly, power should run from battery to headlight switch and then to the dimmer switch?

I do not believe there is a fuse for the headlights although I did find fuse's for the other lights.

Since the headlight switch is getting power to turn on all other lights I'm assuming the problem is between the headlight switch and dimmer switch. Does this sound probable?

That would be correct.... If do not have power to the dimmer switch,,,, Trace the wire

Okay, thank you. I heard something about a welded link as well? Is this between those two switches ?

If it had a dimmer switch,, you should be just tracing wires..... Only thing that got in the way on the military truck was the " Drive By Night Switch Function". Those are the 2 little holes or switches next to the headlight switch. But those would effect all the lighting, not just the headlight dimmer switch.....
Check the dimmer switch for power. If you dont have power to the Hot side. Then you will need to trace the Hot lead and find where it has dropped out....
Your on the rite track.

Okay thanks, will do.

Do you have the wiring info for your 1975 Dodge M880 Mil Spec Truck.... If not... You might look to see if you can get it here>>>>> http://www.imfmotorpool.com/DODGE_M880_Manuals.html

I didn't find one listed for 1975. I traced the wires and can't find an issue. There seems to not be any power coming from the yellow lead on the headlight switch although all others are getting power. Is there something simple I'm missing. I have tried the switch in all positions I can think of. The military black out switch is on the right side of the dash and has three switches. One is to simply unlock the other two to move them. One says ser. Drive/stop light/off/b.o.marker/b.o drive. It is currently in the ser. Drive position. The other says panel brt/dim/off/park. It is currently in the off position.

I downloaded the 1976 manual. Thanks for the link. Still no luck with this dumb switch. Both are brand new.

Also, the old owner ran a wire directly from the battery to the headlights when driving at night. I noticed when you do so the marker lights get dimmer. Is this a low battery indication? Truck starts and runs fine every time.

Trace your hot wire back and see if it goes to a relay, See if that has power?

The red wire goes to a relay and it does have power. I assume this is the only power wire going into the switch. All other lights function as they should through the switch. I replaced the switch again and the headlights still don't work. I'm at a loss of what else I can do.

https://cimg6.ibsrv.net/gimg/moparfo...9e191043e1.png

The above diagram is pretty much the same as my truck. I will post the military diagram next.

https://cimg5.ibsrv.net/gimg/moparfo...85f3794f8e.png
https://cimg0.ibsrv.net/gimg/moparfo...6ff72063ed.png

https://cimg6.ibsrv.net/gimg/moparfo...599396910e.jpg

The wiring colors on the switch don't exactly match the diagrams either I'm assuming because it was modified for Military.

Third one on the left is dark green. Black is behind the white on the right.

OK... I'm a little lost... I'm confusing myself just a little...
1. The head lights do work?
2. The high beams are not working?

The other raised question is. The truck did have a high beam dimmer switch in the truck? or was it added later?
The OEM Shows it
The Military spec dose not

Headlights do not work at all. No power to the post the headlight wire is on. Also no power at dimmer switch post. I believe this truck came with the switch. It may be as simple as the wires not all being on the correct posts I suppose. I marked them as I took them off the old switch and took the old broken harness off.

The other problem has been not finding a single diagram with all the same colors I have. Just to check I put the headlight wire where the red wire is because I knew that post was getting power. The headlights came on, but no dimmer still.

On second thought I may not have tried the dimmer at that point.

Headlights come on and function with dimmer only if I swap the black and green wires, but then I lose marker lights. Both wires must be swapped or it doesn't work.

https://cimg1.ibsrv.net/gimg/moparfo...6390379824.png
this is the original diagram for factory. I do not have a brown and black. Instead there is a red in that position. The black wires crimped into one come from the military harness that powers the rest of the lights. If I put dark green as shown above and the military wires where black is shown I get headlights, but no marker lights. If I switch I get marker lights and no headlights. Was thinking the one showing black is actually a ground. Was Wondering if I could put the green with the black military wires and run a ground wire to the back post. I think when I tried touching the green the black wires I got Sparks and the wires got hot, but I didn't have a ground on the back post. It seems there should be a correct way to wire though without doing that since it was wired at one time and must have worked.

If you can... Take a picture of the headlight switch (one you have out loose) where everything plugs in. I dont have a switch here to look too see what the letters are down inside the switch.

https://cimg4.ibsrv.net/gimg/moparfo...c62753ef4c.png
I stole this off the internet since mine is installed. If it doesn't help I can pull it out for a picture.