TheHandler

Just replace all of the vacuum lines on the '68. Started with the headlights - had the car running for 15-20 minutes while I played around - lights now work as they should. Started to work on the wiper door vacuum lines. Went behind the dash and found what is described as the wiper door solenoid, (see below). It's mounted on the rear of the tach - has two vacuum lines and a two wire connection. When it came time to swap out the hoses, I was surprised to find that the solenoid was really hot - I mean too hot to touch. The heat must have built up while I was working on the lights.

The obvious question is what would cause this? Is the solenoid itself on the way out, or is it possible some wires are crossed out in the engine bay? And what exactly does this do and how does it work?

Any help would be appreciated...

BBCorv70

Too hot to touch doesn't sound right. Do you have access to an ohm meter? Measure across the terminals.

0Willcox Corvette

Okay.. what is the status of the wipers... do they work?

Unlike it's counter part 1969-1972 cars where the power to the solenoid came from the yellow wire circuit, the 1968 wiper system and solenoid picked up power from the brown wire off the wiper motor.

As you can see from the diagram below, this brown wire was only hot when the wiper motor was running and should not have any power on it when the wiper motor is off.

Willcox

TheHandler

Many thanks! At the moment, the wipers are not working. So if what you say applies, I've got some wiring issues out in the engine compartment... sound right? If you don't mind me asking, how does the solenoid work in tandem with the vacuum?

0Willcox Corvette

The solenoid is what blocks the vacuum to the relay that opens the wiper door... For now, if the wipers are not working unplug the three wire connector at the wiper motor... that'll cut the power feed to the solenoid.

You see it where it say's "original connector, not supplied with the motor"

TheHandler

Thanks so much! I'll get into it this afternoon. If the solenoid is nothing more than a vacuum switch, then I haved to assume the heat issue means it needs to be replaced.?.?

0Willcox Corvette

It's just a vacuum solenoid but I'd not assume it's defective until you figure out what's going on with the wipers. Unplug it if the wipers are not working this takes it completely out of the loop.

The solenoid is easy to test, 12 volts to one side ground to the other should produce blocked vacuum. Remove the 12 volts and it should open.

Willcox

7T1vette

"Open" and "closed" means that when you apply [or unapply] 12vdc to the solenoid you will be able to blow through the two fittings to which the hoses are connected....or not. It is a solenoid, so when 12vdc is constantly applied (as when the wipers are on continually) it WILL get hot to the touch. That's why it is mounted to some 'metal' up under the dash.

But, you must remember, when you get everything working and actually drive the car, driving in the rain will be a rare thing!!

TheHandler

The problem thickens. I disconnected the three terminal connection, ("original connector, not supplied with the motor") and the power to the solenoid went off. Strange thing is the ignition key was off. So I have to assume the solenoid has been powered as long as the battery has been connected -- thus the overheating. At this stage of the game, I'm stumped. I can't get the wiper motor to turn on. Pulled the motor itself out and bench tested just to make sure it was functional - and it was. The wiring on this car has been compromised, and the wipers literally haven't been on for 20 years. I'm really not sure if things are connected as they should be. The schematic above is helpful, but at this stage, I need something like a troubleshooting flowchart of the entire system. Something to tell me where the power should be, shouldn't be, and when under any given circumstance. This is very frustrating...

7T1vette

You need to "chase out" the electrical wiring related to the wiper system COMPLETELY and compare it to an ACCURATE electrical diagram for YOUR MODEL YEAR. There are differences in wiring between EVERY model year for these cars.

There are fusible-links involved with the wiper motor (because of the potential for HIGH current draws with a failed wiper motor). Those links can fail internally, but still appear to be viable when you visibly check them out. You need to wiggle the fusible links to see if they are 'crispy critters' internally, or not. If they are, all kinds of electical problems can appear in those related circuits.

P.S. You MUST replace fusible links with equivalent FUSIBLE-LINKS to assure that your car and you are protected from potential fire hazards. DO NOT replace them with 'regular' wire or non-standard items. (regardless of what others might tell you)

TheHandler

Worked on this most of the day. First, I bench tested the motor as outlined in a Willcox you tube video - brilliant, by the way. On occasion, the motor just clicked when powered up, but wrote it off as loose connection. Reinstalled the motor and "chased out" each wire. What threw me off is this system uses grounds like most cars use positives. Here I was looking for voltage when in fact I should have been looking for grounds. Once I understood how the system worked, and with the use of the schematic above, I was able to trace each wire. As the interior is all torn apart, found that my main issue was missing grounds - namely the one that works with the bypass switch on the driver's side. That all said, back to the motor. As mentioned earlier, the bench test revealed a few clicking false starts written off as a loose connection. No such luck. A retest of the system later in the afternoon gave me nothing but a click coming from the motor. I assume it has a "flat spot" and needs to be replace. I'll pull once again to bench test, but the writing appears to be on the wall -- motor is probably bad. Many, many thanks for the help here! Couldn't have done it without you!