Okay, I have Sylvania 9004 lamps.

With both switches disconnected and both headlamps and battery disconnected, I am seeing 525 ohms to ground on the black and red (outer) pins. The center pin (black with white stripe) is not connected to ground.

 

It depends on where you're testing to for the OTHER end.

And if you have high beams, don't you probably have a complete ground?

I suspect a bad test point for the other lead myself; where are you connecting it?

RwP

 

Maybe the 525 ohms is from the filament of a dash lamp in circuit... have to see why my colors don't match up. Thanks for that diagram, different than the Haynes!!

 

Wait wait... I don't have high beams working! No headlights at all were working. Clipping one lead to the chassis by the alternator, then probing with other on the headlight socket when disconnected from the headlight.

My point was should I not be seeing ground on one of the pins at each headlight?? I'm not getting that. I'm getting 525 ohms to ground on black and red leads, nothing on the black/white stripe lead. But those colors don't jive with what I should have according to the chart. I should have violet/white stripe, red/orange.

Maybe they change color somewhere... investigating.

 

And maybe the 1991 is different from the 1992 and following.

Yes, you SHOULD see a return to ground; but, "to the chassis by the alternator" may not be a good enough ground to test to. Try the negative battery cable first.

Chassis is painted, which insulates; besides, the chassis isn't BY the alternator ...

You could use the ground wire attached to the alternator, I suppose.

The "no low beams" is another thread on a 1991; I was confuzzled in my brane because of the similar situation.

RwP

 

OK, next discovery is that there are plow cable assemblies hanging here. Someone had added extra wiring fused right to the battery for plow lights as well as other connections for hydraulics for the plow they used to have mounted on this. I also found that at my headlights I do have a violet/white, red, and black wires. I was not able to see well earlier and there was tape goop on them!

I am going to carefully get this plow cabling out of my way and capped off..

Just to be clear, I don’t have any headlights working at all, no highbeams or low beams… I very much suspect the headlight switch with the integrated circuit breaker at this point. I believe that the 525 ohms I am seeing is the high beam notification bulb filament...

 

Could easily be the filament; hence why I don't measure CONTINUITY TO GROUND ON THE HOT WIRE.

Don't.

Don't EVER do that.

Unless you've got the wiring harness split at BOTH ends, and then, I don't know why you would.

So.

Have you checked for 12V out of the headlight switch (backprobe the connector for that test) when lights are on? Or into the multi function switch?

You know, I'd been checking all THAT before I tore into the front and doing continuity tests around.

I'll add that if you were to fire a parts cannon at it, I'd start with the headlight switch and the connector for the headlight switch; due to the cheap *** poor design of the headlight circuit (No relays? Really, Chrysler? REALLY????) they're prone to failure with age.

After you get it up and running, I'd consider a good relay harness to run the lights off of (one that you would plug into a headlight connector, then plug the lights into the harness, so that the power is carried through the harness, not the headlight switch.)

I like the Putco myself; Amazon shows a 9007 harness at
that just needs to be rewired on the connectors to work. And that can be done like this YouTube video shows:
RwP

 

Hi Ralph,

So I decided to go back to square one with the wiring today. Battery got a full charge overnight on the trickle charger. New headlight switch came in. Not going to put it in yet.

I went back, with battery connected, both headlight and multifunction switches out of the truck, and looked at the voltage at the B1 terminal on the headlight switch connector itself. I had tested this before... I got a good ground under the dash on the chassis and when I measured the voltage there I noticed it steadily declining as I held the meter probe. Started at 12V and within 20 seconds was down to 10.5V. Like my Fluke is loading it down!!

Now that can't be right!!

 

It can be, especially if there's corrosion on where you're checking the ground ... or on the contact. Or on the battery cables, either end. Or if the cable has "green rot" inside.

I'd check across the battery, see if you get that same response. Then from the + post of the battery to the inner fender ground point by the battery. Then if possible the battery connector on the back of the alternator to the - post of the battery. Then back of alternator to good ground somewhere on motor or passenger inner fender. All that to verify you don't see the same action; this would eliminate the battery, cables, and connections.

There's an article on the problems some vehicles have with the bulkhead fitting; it's written for a 70's Mopar, but the principles still hold. The FIX is already on our trucks by design, but there's still a hella lot of current through the bulkhead for the lights ... https://www.allpar.com/history/mopar/electrical.html

RwP

 

Well I think I found the culprit! Looked at the schematic and saw a relatively straight shot to the battery. A splice and a wire link. I disconnected the battery and tested resistance from that B1 pin on the headlight connector to another lead I ran right to the battery terminal. Over 30 ohms!!! Jiggling the connector around and wires under the dash, I got it as low as 10 ohms at one point but the average resistance was 30 ohms! So I knew there was a load inline that didn't belong there.

Start tracing that red/white stripe lead back and here it was all corroded to hell at the firewall connector! A handful were acutally.... I could see it from the underdash side even.

When I got the connector apart it some terminals were so rotted that they broke apart and stayed in the connector...

So I guess next move is ordering both sides of the connector and rewiring that rascal.