The wipers on my 75 do not work.  The wiper motor does work.  I am able to connect the wiper motor terminals to external battery. 

if i understand you correctly, you are getting a 12v reading on the positive wire at the motor.my suggestion would be to take a wire and connect it to the negative side of motor and ground it out. you would be bypassing the negative wire and if wipers work with the extra wire grounded then you would have a bad negative wire. hope this helps.

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LIFETIME MEMBER #97
THE DYNAMIC DUO

The wiper motor works off of a ground signal from the switch. Sorta back-wards from "normal".
The wiper motor should have 12v anytime the key is on. The switch provides different ground paths(resistance) for the different speeds. Check to make sure the wiper switch itself is properly grounded first. More than one person has spent days trying to figure this one out, only to find the wiper switch wasn't screwed into the dash correctly, or...the plug was up-side down!
Run your jumper wire from a good ground to the wiper switch casing, and see what happens.

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

figures they would make it bass ackwards to confuse the heck out of everyone.  good thing joel was here to save the day.

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LIFETIME MEMBER #97
THE DYNAMIC DUO

David/Joel,

The switch itself has to be grounded to provide a ground to the wiper motor. You need to correct that first. The switch normally has a small wire attached to one of the screws that hold it to the bezel. If your's doesn't have this wire, try putting one on it from a good ground source. I think this will solve the problem.

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Joel,

Excellent gentlemen ! The first problem we encountered on the trip to the gathering was the wifes wipers came on and went off by themselves, leaving the wipers in the middle of the windshield. had to remove the arms entirely. I very much appreciate the education BEFORE I get started on it. I'll get 'er done in a short time.

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Jimmy B.
Just can't wait to get on the road again.

 
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[QUOTE=Adams' Apple] The switch itself has to be grounded to provide a ground to the wiper motor. You need to correct that first. The switch normally has a small wire attached to one of the screws that hold it to the bezel. If your's doesn't have this wire, try putting one on it from a good ground source. I think this will solve the problem. [/QUOTE]

Otay...after reading this again, I feel I should clarify my statement...

What I should have said was, "The switch usually has a small wire attached..." because that's the only way someone else could get it to work!
In reality, the switch is supposed to be grounded by the bezel, which is a cast metal piece, and is screwed into a metal part of the dash cross-bracing. That's the way they were...by now, however, the bezel has been in-out of the dash 100 times, and it is no longer capable of providing the wiper switch with a ground, and that is normally because the screw hole threads are stripped, or the particular screws are not even there anymore. That's why most of the ones I see have the extra wire-ground added.
Also, the wipers will not normally work if the bezel is un-attached to the dash...another reason for the extra wire!

Sorry if my statement was mis-leading, or, heaven forbid, confusing!

need sleep...

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Joel Adams
C3VR Lifetime Member #56    
My Link


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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Let me just add, if the extra ground wire is not on the switch, put it there just to avoid problems in the future.

 Hey guys!  I added the ground wire from the wiper switch to the mounting screw and it did not fix the problem.  Could there be a loose ground wire or dirty terminal under the dash?

Check to see if you have power coming from the wiper motor to the switch.  You could have a bad connection somewhere along the line.   Also check to see if the same color wires have power coming out of the motor.  One wire will have power going to the motor when the ignition is on.  If you have power anywhere, that's okay, but you could have lost the power supply altogether.   Keep in mind a very poor connection will show voltage when the circuit is not operating, but when turned on it could drop to almost nothing.