OK all you electrical wizards here is my problem.

1970 Corvette with power windows. Drivers side window will roll up but not down.

I took the door panel off and got access to the motor. Removed the electrical connector from the motor. I connected my Simpson meter to a good ground and then started probing the connector for power. When I activate the counsole switch I get battery voltage on both terminals (up and down).

Thinking I had a motor problem, I removed the motor and got it on my work bench. Took my battery charger and applied 12 volts to both up and down connectors. Motor turns freely in both directions.

Now here is what I think. The down wire is actually broken , probably inside the door hinge area (inside that little rubber conduit) and there is but a single wire strand still holding on. That little strand will give me a voltage reading but won't carry enough current to power the motor.

Am I missing something here? Could the relay or console switch be bad?

Is that rubber conduit replaceable? Can I disect it to find my broken wire? If not replaceable, what techniques did you use to get the wire harness out in the open where you could repair it?

Bob

Any help is appreciated.

 

Common grean grass switch failure...without load the carbonised switch is likely to say anything to a NO load DVM....

gotta put a load on it with the motor to see what's what....

or at least a lightbulb....

 

The meter that I am using is a Simpson 260 analog meter, not a digital unit.

So you think the switch on the console is the culprit?

I can check the voltage to both terminals with the motor connected. Will give that a try and see what happens.

The voltage reading with the motor running will obviously be lower than without a load. Either way, the bad wire or switch cannot be isolated just with a voltage reading.

Guess I just need to get a little deeper into the wiring harness. The console switch is pretty hard to get to otherwise I would just jumper around the switch and isolate it that way.

Thanks for your thought.

Bob

 

I think you seem to be on the right track. The rubber conduit is available from many of the Corvette vendors. I had a similar problem and I disconnected the plug from the motor and fed the wires back through the door. You need to do this to replace the rubber conduit anyway. Once I got the conduit removed I saw that the wires were cracked and frayed. Then I spliced some new wires in the section that passes through the door. These wires are 30+ years old and the dry out and get brittle. Open and close the door a couple of thousand times and the wires fray and break. You need to get in there and look but I believe you are on the right track. If the motor doesn't turn it is either a motor failure or an electrical issue. You seem to have eliminated the motor problem.

Another issue I had was itermittent motor operation. This was caused by build up of carbon on the motor brushes. A couple of taps with a hammer cured the problem in the short run. I eventually had to replace the motor which was cheaper than getting it rebuilt.

 

No wizard here but to me it sounds like you are on the right track. I would hook the motor up outside the door with no window load and try again. If it works the window could be part of your problem or as you said earlier a broken wire not carrying the load. I would think the next logical step would be running a jumper wire.

 

Guys,

I have already run the motor outside the door with my battery charger. I too thought the commutator had built up an oxide. I ran that motor several minutes in both directions with no problem. Did take this opportunity to relub all the motor gears and the regulator tracks. No real rust problems there as the car only has 39000 mls. It is a hanger queen.

I have taken the rubber conduit out of the door and have begun to inspect it. So far, there is good continuity between the wires in the door jam and the motor connector. What is holding the console attached at the rear? Is there a screw or bolt that goes thru the rear cargo area that holds it in place. I really want to jumper that switch and eliminate it from the sysem as a probable cause.

Bob

 

Yes ther is a screw comming in from the center storage compartment.

 

Do I have to take the entire storage door assembly off to get to the screw?

 

I think you can just open the storage door and get to it. It should right above the drive shaft hump.

 

For the motor to work, you will need a supply voltage and a return path. There should be two wires, one from the down contacts on the switch and one for a return to battery. Put the meter across the two disconnected wires in the door and press the down switch. You should read 12V. Because you have already checked your supply voltage against a good ground, if you do not see 12V, you probably have a problem with the return (ground) wire.

Connect the motor, press the down switch and read voltage across the motor. It should read about 12V. If not, check the voltage dropped across the return wire with the motor connected and the down switch pressed. The return wire should read only a voltage drop of a few millivolts, if you are reading more than that you have a high resistance connection to ground and are dropping too much voltage across the ground wire for the motor to work.

 

On my '69 there is no screw but if there was I would have to remove the storage assembly.

 

Bob3700,
Same problem on my 74 d.s. window.
Broken wire in rubber boot of door. glassman74

 

Well here is what I found today.

First, access to the console rear screw is thru the rear compartment where the jack is. Take the false tray out of the jack compartment and you can access the rear screw easily.

Now the electrical problem. I removed the console and gained access to the window switches. The switch has continuity from supply to both up and down positions. I reconnected the wire connector and put battery power to the vehicle. Window rolls up and down!

I believe the problem is with the actual connector on the back side of the console switch. The connection is intermittent on the Down side of the switch. The brown wire (window down power) is loose in the connector and may not be making good contact with the post on the switch. Will have to see just how I can remedy that.

Thanks for all the help guys.

Bob

 

Told you the switch was bad, right off the bat, and to confirm with your voltmeter.....most guys have a DVM these daze, even I being an olde phardt ditch my 260 some 25? years ago....

 

Replace the switches. If one is bad now, the other will be "biting the dust" soon.