After bringing my 72 out of a long 3 year sleep, I'm having a strange power
related problem that only effects the radio and windshield wiper motor.
After reviewing a couple of wiring diagrams, it seems that the two share a
common feed from the ignition switch to the fuse box. I replaced the
ignition switch and thoroughly cleaned the fuse box & bulkhead assembly
having no impact on the problem. There is a radio capacitor in this wiring
circuit mounted on the side of the steering column. Could this capacitor be
causing an intermittent power problem? Sometimes the radio and wipers work,
sometimes they don't but always together (working or not). I checked the
voltage at the fuse assembly when they are not working, and only have around
4 volts at each of their respective fuses. This again points back to the
feed from the ignition switch and/or the capacitor. Any suggestions would
be greatly appreciated.
Depending on where it was in storage, you could have had mice. So you may
have to check the wiring from where you know it is constant to where it is
intermittent for physical damage.
You could have switch corrosion that is causing intermittent contact.
Sometimes the switch is on, sometimes it isn't. You may get it to clean up
by simply switching on and off many times rapidly or you may have to use a
switch cleaner, like you can find in electronics and TV shops.
Fuses are probably fine, but you could take each out and reinsert in case
corrosion has begun to isolate their electrical contacts.
The capacitor can break down over time and could have been aggravated by the
long storage if the heat was too much, like a closed metal building in the
desert, however, it would probably have failed without the storage, although
maybe a little later. However, that is an easy check. Just unplug it.
I completely dissembled the fuse box and bulkhead assembly, cleaned them
thoroughly, and used a high quality dielectric grease on all fuses and
related connections. I also removed the LH dash, center gauge cluster, and
middle console and cleaned all connections and used dielectric grease when I
reassembled the harness. I found a few prior owner repairs that were
questionable in the dash wiring harness and made the necessary corrections.
I also found a broken wire in the wiper motor assembly, so I rebuild the
motor and made all internal wiring connections per the GM shop manual.
After getting her back together, I headed out on a several hour journey,
radio blasting away, and after about an hour the radio quit. I tested the
wipers and nothing there as well. After the car sat for a couple of hours,
I started it up and both the wiper and radio were fine, but soon quit again.
Today I took it around the block and when I hit the horn, I received a mild
shock through the LH door. With the window down, I rested my arm on the
window channel, hit the horn, and received a shock again. Sounds like I
have power going to ground, maybe at the horn contact? Since this problem
began, the switch cylinder and sector gear broke in the column and I pulled
it out and replaced the failed parts. While the column was dissembled, I
inspected the turn signal harness and everything was in good condition
there, so the problem must be in the engine compartment somewhere. The
other response to my post recommended putting an additional ground on the
wiper switch. There is an additional ground wire (had good continuity) from
the switch to the center gauge cluster. I carried it on to the radio and
then to the transmission drive selector mount (good ground there) and it did
not fix the original radio/wiper problem.
I will also try your suggestion and remove the radio capacitor, but it looks
like there may be a ground problem at the horn contact, steering column, or
somewhere between. Any further comments would be appreciated as the two may
be unrelated. By the way, today neither the radio or wipers worked.
On or about Wed, 26 Jul 2006 19:04:22 GMT, "Kelly W. Zini"
12 volts is not enough to cause a shock. Try wetting your fingers and
place one on the positive battery terminal and one on the negative.
If you really insist that you felt a shock how about a bad ground on
the steering column and a plug wire too close to the column? In any
case, this isn't your wiper/radio problem.
A capacitor can fail shorted but they then usually explode. They most
often fail open. Again, I doubt this is the problem. If you have a
power supply strong enough to run a wiper motor, it will blow a fuse
or fry anything that tries to short it out.
The fact that it worked for a while indicates that it is very likely
something that looks physically good but has a minor mechanical
problem. Since the radio/wiper is not working now, you should be able
to identify whether it is power or ground that is missing. When you
said earlier that you had 4 volts at the fuses, that tells me you have
a power problem (as long as you were measuring to a KNOWN good
ground). As long as they are not working, go through the power again
being very careful not to wiggle things any more than necessary. If
possible (and I don't know why it wouldn't be) leave the radio on
during your testing. If it suddenly starts playing you know you have
just wiggled the bad connection.
The shock comes from the release of the horn button. This disconnects
the connection to the Horn Relay. The magnetic field collapses,
creating a large voltage spike where there had been 12VDC. This is
returned to the horn button (if not insulated) The circuit is completed
when a ground point is being simultaneously touched (the LH door).
cause to be written:
Agreed, IF, you have a horn relay with one end connected to positive
and the other connected to a bare metal horn button which, when
pressed, contacts a ground, then when released you would get a large
voltage on the metal button. This, however would only happen in a
system working properly with a good ground AND one that did not have a
capacitor or diode across the relay. The horn would not sound if you
did NOT have a good ground and good power. In this design, the metal
button would always see a large spike in voltage when the ground that
was causing the relay to pick up was released.
In any case, it still has nothing to do with the radio and wipers not
working. You had to have both a good ground and good power to get the
horn to work. A missing or blown diode or capacitor across the horn
relay and a bare metal button connected to the relay and contacting
ground to complete the circuit are also required to get a shock.
Eliminating the shock would require wearing gloves or covering the
horn button so that the driver can not make electrical contact with it
and/or adding/replacing a diode or capacitor across the relay coil.
None of these should have any effect on the radio or wipers.
None of this suggests ".. I have power going to ground, maybe at the
horn contact?" If there was indeed a shock, it is a separate problem.
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