Electrical Gremlins, HELP!!! Options

[richardL]

So my car ran the other day without problems. At first there seemed to be electrical issues, then they miraculously went away and now they are back.

Now its completely dead on the ignition switched circuits.

The car has carbs and hence no FI, most of that wiring is removed.

The battery is charged, the parking lights work and the instrument panel lights come on as well, the green parking light light as well.

I thought there was a problem on the ignition switch, so I have a brand new race style switch. Power in, switched power out, starter out.

With the ignition off I am getting around 13 volts at the switch. When I turn on the switch I get 0 volts. I disconnected all the three output wires (red, black and a thin red, which I think is for the voltmeter) and then I have 13V at the output terminal of the switch. If I connect any one of the three output wires again I get 0V. With them disconnected, if I try the starter, momentary switch the voltage goes to 0V - the starter doesn't try to turn or anything.

I removed all the fuses, just in case, and it has no effect on the above symptoms.

I also have an external kill switch and I always seem to have the expected 13V at the output of that, even when the ignition is switched on and doing nothing.

I am confused, as any kind of connection seems to kill the voltage, yet the battery seems OK and can support side lights at least.

Am I missing something obvious? Am I being dumb? How should I go about diagnosing this? Any suggestions would be very gratefully received.

Richard

[Otmar]

First off, if it were really a short you'd be getting either smoke or a blown fuse. What you are looking at here is a high resistance connection. This connection looks fine until you put a load on it, at which time it measures much more like a open circuit.

Mike is right on concerning the diagnostics.

When you mentioned the voltage from the cutoff switch to ground falling to zero, and I'm assuming that this cutoff is right by the battery, it makes me think you have a bad connection very close to the battery. Possibly in the ground cable too.

You can bridge your voltmeter on each connection (post to battery clamp, clamp to cable, cable to bolt etc.) and anytime you get a voltage reading accross a connection that is supposed to be connected then you've found your problem (do this while the key is on, or whatever you do to cause 0 volts to ground at the cutoff switch).

Or, following the old addage of "When you hear hoofbeats, don't think Zebras" you could just clean your battery terminal connections and see if it fixes it. Don't forget the connections to all those red wires that come off the battery, they are usually a problem too.

HTH,