Hello everybody! I know I'm new here and all, but this is for a friend. His 1977 Corvette with factory alarm system had a windshield wiper system failure. I'm a retired electrician with little automotive savvy, although I have fixed a few in my day. Anyway, he has a sad story and is strapped for cash, so I went to take a look.

With a Fluke meter in hand, I pulled both connectors off the motor and checked the center socket on the plug to make sure I was getting voltage to the motor, with the Ig-switch in ACC. Found 11.5v referenced to ground terminal on wiper motor. With the hood alarm interlock by-passed. Plugging everything back together and attempting to operate the wipers, 2 speed sw on turn signal stem. The motor won't run.


Took a look at his Haynes manual, ( I hate these things) and the unit looks like it has a dc relay and a mechanical reversing switch inside the housing. I pulled the cover and used a spare 12v auto battery to check the relay. It pulls in just fine. I do a little live checking, and I can make the the motor move back and forth electrically but it's sluggish. I'm doing this with just two terminals of the motor hooked up at a time to the battery, so I'm not sure if the circuit is fully across the battery. I figure he has a problem somewhere in the car wiring. I suspect a bad wire, because he's using an electrical choke and had the hot side connected to the center terminal of the wiper connector, which gives him 12v to the choke when his ACC switch is made. He doesn't like that idea, so he goes and buys a new W.W. motor. After R.&R. and plugging the new one in, it won't work either. No big surprise, but just to be thorough I tried using the battery to drive the new one. I can't get this one to go though, which has me stumped! This unit came with an extra ground strap about 5/16 in. wide and an adjustment tool which I gather from the instructions, they're pretty generic too, is used to align the mechanical sw./drive shaft assembly, to assist in mounting the wipers, although that seems improbable, because it has a homing latch, which is where the unit is set, out of the box.

So have I entirely missed something or what? Does that grounding strap have to be removed? Does the alignment tool release something mechanically before installation? I swear the instructions are very vague.. Should it be possible to operate a new wiper motor with just a battery and a couple of wires? The wiper motor that was on the car was original. Did they change the design inside at some point? The original problem seems a little baffling too.

He did tell me when he first got the car, he had trouble with the hood interlock sw. for the car alarm, and that kept the wipers from working. Replacing the switch solved the problem. He now has it bypassed to troubleshoot this problem. I'm curious too where GM put the electronic module for the alarm? If anybody can give me any pointers on this, I would appreciate it. He's a really good guy, who's had a streak of bad luck lately. I was hoping to turn it around a little for him.

Thank you in advance and hopefully I can return the favor.

Why is the wiper and hood alarm system interlocked? Is it drawing the circuit voltage down too much? I'll have to take another look when I get home. I presume you're testing it without the linkage attached. There's no such thing as a good wiper system from the 70s. How fast are you expecting it to be? Is it supposed to have two different speeds?

My guess is that according to my friend the wiper power lead is the recommended spot to attach and pull power for an electric choke. So it's one of the ways to disable the car so that it can't start. He has the switch bypassed so that with the hood up and the ACC On you get power to the wiper feed wire. He even went so far as to remove the choke from that circuit and source the chokes' power from somewhere else. The car starts and runs no problems. We have been testing without the linkage attached. It's a two speed wiper system.

Well as far as the speed, I would estimate third or at best half of the speed you would expect. What really concerns me is that I couldn't get the new one to work at all.

Well I kind of figured out a couple of things while puzzling over the Haynes manual. The 3 terminals coming off the wiper motor are hooked up, 12V center terminal and ground on the end terminals. I think that the spring/relay trip mechanism has something to do with keeping the wipers down at the bottom of the windshield. Surely a control box is stashed somewhere hasn't anyone ever messed with theirs, here?

Wish I could help, but that's one of the few things I've never had to touch.

Best of luck!

Well thanks for the moral support anyway. I'm going back over to my friends today to have another go at it. He's going thru a divorce and couldn't work on it yesterday. If I get this figured out I'll write up something and post it here. That way anyone who comes here will have some further guidance. Have a good one Trae..

Hey ROM, have any luck yet?