'75Electric wiper motor problem?

[reamer]

Hi All, On a bench test I ground the black wire, then I apply 12 to the Blue and the motor spins...... then apply the 12 to the White and the motor spins slower,
On the truck harness, with key on, and wiper switch turned 1 click, I get 10v at the White, ...switch to high on wiper switch I get 12v. on the Blue.
This proves; 1. Motor works.
2. there is power in the harness with Key and switch on (in high and low positions)

So now I plug in the motor to the harness and I get nothing, Motor will not spin,, Even with a dedicated ground directly back to the battery neg terminal.
What am I missing?
Thanks

 

[Viperwolf1]

You should have 12V on both blue and white-black in their switch positions. This tells me you have a huge voltage drop in the switch or wiper wiring. Big voltage drop means a lot of resistance and not enough current to get your motor running.

The park circuit wires are not necessary to make the wipers run, so don't waste effort looking at those yet.

 

[DirtDonk]

Did you ground the motor case? The Black wire on a wiper motor is not always just "the ground" for the motor. Might be something else.
Either way, add a battery ground to the mounting bracket, or motor case.
That sound correct Phil?

Paul

 

[Viperwolf1]

Did you ground the motor case? The Black wire on a wiper motor is not always just "the ground" for the motor. Might be something else.
Either way, add a battery ground to the mounting bracket, or motor case.
That sound correct Phil?

Paul

Correct. None of the 4 wires on the motor is a ground.

 

[reamer]

Did you ground the motor case? The Black wire on a wiper motor is not always just "the ground" for the motor. Might be something else.
Either way, add a battery ground to the mounting bracket, or motor case.
That sound correct Phil?

Paul

Hi Paul, yes dedicated ground directly to the battery..