I need some help figuring out my nonworking wipers.

1991 F150 302 non intermittent wipers.

The voltage gauge is dropping down and there is a humming noise coming from the wiper motor.
The noise is corresponding with the gauge drop.
I replaced the motor today and it didn't fix it.

Any idea what I should be checking next?

 

Check to make sure something hasn't tangled up in the wiper arms.

Had this happen in my old T-Bird. Bought a new motor and put it in the pouring rain. Still didn't work. Took the plate/vent off under the wiper arms and an old shop rag had tangled into the wiper arms binding them.

 

I took the cowl completely off so I had a good view of the linkages. It all looked good.

 

What happens when the power to the wiper motor is disconnected?? Still the noise and the voltage drop??

 

When I disconnect the noise quits and the gauge goes back to normal.

It is the two plug motor.

 

I would try disconnecting the linkage--especially if the cowl is still off/loose-and then reconnect the electric plugs and see what happens.

 

Ok I'm confused maybe someone can help me figure this out.

The wiper motor is a two plug and when I unplug the top plug my wipers seem to work fine.

When I plug in the top plug the voltage drops the engine starts running rough and the wiper motor freezes.

And the wipers are intermittent I was mistaken.

 

What color are the wires going to the plug that is causing the voltage drop?

 

red, black, black/red stripe

 

Could it be a a bad ground?
How would I check?

 

It's supposed to rain tomorrow and I still haven't figured this one out.
Pretty much I have run out of ideas.
If anyone has any ideas I would appreciate it.
Thanks

 

Unplug the top plug and let it rain and let the wipers work. We will have to get back to you and figure out what the top plug does and why disconnecting it doesnt effect the operation of the wipers--per your previous post.

The ground can be checked by taking a DVM-set it for DC voltage and take one side of the meter to the negative side of the battery and the other to the ground of the wiper motor. I dont have a wiring diagram of the wiper motor in front of me at the moment. If the ground is bad-you will see voltage on the meter when the wiper motor is operating. But let someone take a look at the wiring of this wiper motor first-and we will get back to you.

Its going to rain??? Where are you located anyhow??