Hi All,

A previous owner installed a long L88 hood and fixed headlights on my 1972 Small Block Corvette w/AC. The wiper door was removed along with every supporting electrical switch,solenoid and relay. The the under hood wiring was hacked up. The entire vacuum system was pulled.

I recently fabricated a simple vacuum storage system to get the HVAC working again. I'm currently working to get the wipers working again. (I think I have a bad ground to the relay).

Since the tachometer solenoid was missing, I fashioned a jumper to complete that circuit. (light blue to yellow wires) and installed a used wiper relay (under the console). No joy yet, but I've still some things to check.

Here's what's got me stumped: I connect my multi-meter to (any) key-on powered wire and I get the expected 12VDC, but when I turn the key-off, I see a very slow voltage drop from 12VDC down to about 3VDC, taking about 30 seconds for the drop. Every other car I ever worked had an immediate voltage loss when the key was turned off. I disconnected the ignition coil and alternator in an attempt to isolate the component that's retaining the voltage. (ignition coil wire experiences the same behavior)

The only thing that I can think of is, there must be a hidden capacitor somewhere in the system. Is this something normal, or potentially damaging to any of the electrical components?

Thanks,

John

 

what is the condition of your battery?

 

I would not worry about it. It could be a capacitor. Could be considered a positive thing, as is shows no parasitic drains.

I like to use a test light for troubleshooting, it shows that a circuit can source power into a load.

 

Considering that the input impedance of your meter is probably in the megohm range, I think this might be normal. There are probably some charged caps in the radio. At any rate, as long as your battery voltage doesn't drop too, you're OK.

 

One of the first things to check is see if you have any voltage on the wiper motor case/frame with the key on or off makes no difference....that frame is grounded by a black wire that is joined by one from the HVAC blower motor and the high speed blower relay on the evap core box.....what happens is it is very common for the ground wire that goes on a bellhousing bolt, or maybe starter mount stud, mistakenly gets connected to the Battery +12 wire on the solenoid so none of the stuff works....I fixed my car decades ago so that wire is grounded to the intake manifold up top.....

 

Hi everyone,

Thank you for your replies. My reply to your comments:

1. My battery is like new and fully charged.
2. My test light also slowly dims down, voltage at the battery seems unaffected.
3. I'm using a Fluke 23 Multimeter on the "auto" setting, displays voltage to .01 VDC.
4. I made the same ground wire mod as mrvette using 10ga wire, resistance reading between .002 and .003 ohms. No voltage on the wiper motor case.

Just haven't seen this kind of electrical behavior before..... but I'm happy to hear that it doesn't raise any red flags with anyone.

John