ChattanoogaJSB

My buddy has a stock 71 convertible which is unmolested and stock. The wiper door and headlight vacuum system has been in good condition until recently the following happened-

On cranking the wiper door will briefly rise partway. It stays closed when parked and when the engine fires it immediately returns to the down position. The override on the right side under the steering colum obviously vents it open correctly (a simple vacuum dump as I understand).

However- the wiper motor has abruptly stopped working when the wiper button is moved to either high or low speed positions.

I note #1 that at the three- wire plug I read about on the CF we have 12+ volts to the middle contact which is always hot.

I note #2 that you can hear a "switching" sound at the motor as we move the switch on the center console. Makes me think the switch and its ground is good, as well as the relay. Maybe not?

I note #3 that the main manual motor control under the column will not force the motor on even with the door open.

I note the valve under the wiper grill is connected to the relay and acutator. Even though the wiper door opens its my understanding that this valve includes wiring which determines if current can pass to the wiper motor. It has not been adjusted but a screwdriver on the "foot" bellows does not have any effect on making the wiper motor kick in. Do I understand this part correctly? Should I bypass it temporarily and how is the best way?

If anyone has any other advice please let me know.

We are a little baffled and I am all the way across town from the car, so I'm trying to collect information (including some excellent posts and links here) before we can get together to work on it again.

Thank you,

Benton

ChattanoogaJSB

Moderators- my apologies I posted this in "general" (c1/c2 doesn't have tech/general distinctions my apologies).

If it should be moved to Tech could you move or for me?

Alan 71

Hi C,
The vacuum override under the steering column should be pushed up. Pulling it down bypasses the vacuum controls and opens the door.
The switch under the steering column should be turned to the right… clockwise… turning it to the left turns off power to the wiper motor.
The vacuum valve in the wiper bay controls the door only… it has no electrical function.
The wiper door limit switch on the firewall must be closed by the wiper door mechanism for the motor to operate.
The wiper solenoid valve on the back of the tach is activated electrically but sends a vacuum signal to open the door.
Have you tried to test any of these parts individually?
Do you have something you're using as a guide to try to work on this?
Did the wipers work properly recently?
Regards,
Alan

Limit Switch on firewall to the right of wiper motor.


Wiper solenoid on tach.

ChattanoogaJSB

Alan- first of all my sincerest apologies for being away from the post so very long. It's unusual for me and wanted to make sure you know I appreciate your post.

I have seen the Wilcox write up on rating various components and I believe my friend has an AIM and a FSM.

We didn't get to work on the wipers last weekend as I had hoped.

The wipers did work recently - stopped suddenly. The door operates fine except that as I note it has started to raise faintly on cranking only.

The switches under the column we have made sure are all in order. There is 12v to the middle of the wiper motor plugin. The switch on the instrument cluster activates the door and the motor makes a "switching sound" but does not energize the wipers.

I'm going to read more and - because it's a great suggestion- learn more about that limit switch in your photo among other items.

Thanks again!

Benton

GlenJack

I am having a similar issue and am standing by, watching.

brent319

My wipers quit on my 76 and it was a bad ground at the switch. Not sure if it is the same for your year, but it would be worth a check. on mine the switch picked up ground off of the bezel which picked it up off of other parts. I ran a grounded wire to the screw that holds the switch to the bezel and was done with it. I wonder if you just ground a wire and touch it to the bezel and see if they work. May not be it, but it would be easy enough to check.

Alan 71

Hi Benton,
I would want to say to check the limit switch on the firewall or the over-ride switch under the steering column but since you're hearing a sound at the wiper motor the problem is likely at the motor.
I think the Willcox wiper-motor test video is your best guide to getting this fixed.
I'm a really poor electrician so I really can't be more help. Sorry!
Good Luck!
Regards,
Alan

DUB

Benton,
If you are at your friends house where the car is at...and try to find the problem...and still can not find it...you can call me. It is not a problem.

The vacuum operating system is very easy to understand and diagnose.

The electrical system is quite simple also...once you have a countless repairs of them under you belt.

If interested....PM me if you do not already have my number.

Using WIllcox's bench test or circuit test for the operation of the wiper switch will tell you a lot.

DUB

ChattanoogaJSB

Thanks again to Alan, DUB, Brent, everyone- I promise I will post the resolution. DUB- it may be a day or two until I get to the car to test anything, but I will read the Wilcox (sp) sheet again as far as testing the motor goes and take you up on the phone call if I can't resolve it. You're kind to always be on hand for so many of us.

Benton

DUB

If you need me...you know how to get a hold of me.

DUB

0Willcox Corvette

Guys all his info in on my repair site for you to view, upload, save and whatever you want.. For free.. it's easy to find too.. just enter your year, then search "Wiper" and you'll pull all the info. http://repairs.willcoxcorvette.com/

Here is everything I have for you on the 1971 wiper system. First you should upload this file:

1969-1972 Corvette Windshield Wiper Motor Tech Help, Wire Schematic With Test

The wiper relay is located here on the 1971 cars.


Here is how you test it:


Wiper relay testing video


Wiper switch testing.


Wiper motor wiring diagram made simple


Wiper Motor testing with some Relay help


Wiper Motor Bench Test 69-72

ChattanoogaJSB

I'm sorry for the overdue update- I do try and update threads so people can use this forum as an archive (I try to!)

dub and willcox- thanks men!

We finally turned our attention to the issue last weekend at my place. I was testing voltage at the limit switch on the firewall, and had briefly jumpered it with the door manually open.

I found voltage low at around 4 volts. It "felt" like a poor ground and so I used a set of alligator clips to jumper the ground on the wiper motor to the exhaust manifold. Instant success!

I added a new ground after the original one failed to clean, and all was right with the world. I need to look over the wiring diagram at his place and see if that poor ground is affecting anything else potentially.

Thanks for taking time to help everyone,

Benton