Electrical issue Power Wagon

Hi, have a 73 Power Wagon and I’m trying to track an electrical issue..
When I turn on the headlights the wiper motor runs. It doesn’t matter what position the ignition key is in and turning the wiper motor switch on or off has no effect on it, it continues to run.
The wipers don’t actually work, but the motor does run.

I pulled the dash and nothing looks hacked or spliced, everything looks factory from a wiring standpoint. I checked all the harness plugs at the firewall under the hood and everything is clean, nothing is corroded or burnt.

Don’t know much about the truck, got it last year on eBay and just starting to mess with it .

Any ideas on what to look at first?

Thanks in advance

look at all grounds. it should have a ground from battery to block and small wire from battery to core support. make sure you have all grounds. even add some made from jumper wires just to test systems. make sure firewall to engine ground is there. good luck.

I have a ground from the battery to engine and one to side of radiator. Have a braided cable from engine to firewall. I’ll double check everything.

bad wiper switch?

So I have to assume when you make this comment there is no linkage attached to the motor? Wipers are keyed power and the headlights are constant power. I would unplug the motor and switch first turn on the headlights and see what wire is now hot. Then trace it back and you will most likely find the problem.

Finally got a chance to look at this again.

I pulled the cowl cover and the wiper arms are connected. I moved the motor around a bit and the wiper arms pivots now move. The motor was seized.

However....even without a key in the ignition, the wiper motor comes on when I turn on the headlights. So the motor is getting power even without a key. I’ll trace back from the wiper motor and see which wire is hot. The wiper switch has no effect on anything.

I've read that some folks have run a ground off the case of the wiper motor itself to a spot on the firewall, because the motor is not grounded well enough to the firewall on its 3 mounting points.

I've done that, went to go to work one morning and wipers wouldn't work. They worked the day before. Added a ground from the motor to the firewall and problem fixed. Only one I ever had to do that to in the dozen or more D/W series trucks I've had. But his problem is the motor running when the headlights come on. Wonder if there is a crossed wire....maybe at the bulkhead connector?

Grey wire from the wiper motor switch is hot when I turn the headlights on even without a key in the ignition.

Given that the wiper motor switch is keyed power I’m wondering if there is something screwy with my ignition switch or wiring. Just not sure how it’s tied to the headlights.

I’ll keep tracing.

Wondered if the wiper motor wiring is shorted to some other hot wire (insulation burned or scuffed/chaffed) ? Have you disconnected the wiper motor? With the connector disconnected it shouldn’t run unless the wiring IS shorted to a Hot wire somewhere in the harness.

Or, if the wiper motor does not meet resistance, like when it bottoms out, it cannot “Park”. When it “Parks” it shuts the motor off. Otherwise, it just runs and runs.

I (also) own a ‘74 W200.

I have disconnected the wiper motor. When I do this it won't turn on when I turn on the headlights.

ai in the engine won't turn over?

As in the wiper motor won’t run in answer to D_C’s question.