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

[Dr Evil]

Hey Richard,
Let me see if I can understand; when you turn the switch to "on" and measure voltage, are you measureing from the switch to ground or across the switch? The latter should produce a 0V state as the switch should effectively drop 0V. If you are measureing to ground and you get 0V either your switch is bad, or there is a short in the system sucking all of your juice.
The best check to see if your battery is bad is to put the meter across the two terminals of the battery (should be around 13V) then turn the switch. Your voltage should drop a little, but anything around the 9V and below may indicate a proble. Consequently, a short in your system will also present with this symptom. Be careful of a short as there is a possibility of fire.
What realy concerns me is your kill switch. If you are getting a constant 13V at that regardless of your ig switch situation then I would say that is likely your culprit.
Figure it this way:
-If you get volts to your ig switch then all things leading to the ig switch are fine. Not Kill switch if it lies before the ig switch.
-check that you get actuating voltage at your starter (little wire, should be 12V when key is turned). If so then everything to your starter is functioning. you must have 12V, no less or you will have to clean up your start circuit as it is dropping to much voltage.
-you can take a large metal tool of your choice and cross the terminals on the back of the starter to see if it is working (not for the faint of heart, lots of sparks). If the starter turns then your battery is good, and your solinoid may be shorting out.

My guess would be that the kill switch, or the starter solinoid is the problem. If you are droping all of your volts then the solinoid may have an internal short. Start with the simple and go from there.

Sorry for the length, but I was trying to cover every contingency.

Mike

[3d914]

Richard,

I feel your pain. I am no electronics wizard, but I have had some success solving these problems - which I attribute a great deal to having a good schematic or wiring diagram.

On my 914, the previous owners have changed some of the wiring, so you can't always trust what's there - even if it has been working.

I strongly suggest picking up one of the popular 914 service manuals - or a couple. Make sure it has the wiring diagrams. That way you can systematically trace & elliminate each relative circuit.

Every experienced auto mechanic relies on proper diagnostics. Without it you're just shootin in the dark.

Good kuck, and keep us posted.

[richardL]

The Kill switch is the first thing in line after the battery. The output of the kill switch goes to (among other things) the ig switch.

When I have any wire connected to the output (for instance the black that goes to post 15 on the ig switch usually) the voltage at the input to the switch (measured from the post to ground) drops to zero - as you say I expect a short. The problem I have is where?

When the ig switch seems to be shorted I still have 12.85V at the battery and the same at the kill switch. Yet at the input to the ig switch I have 0V!

If it were in the wiring beyond the ig switch I would expect the starter to turn when I close that part of the switch, but the voltage goes to 0V as well. So I don't know if its the starter solenoid. But if it were I would expect to only see a problem when I try to turn it over. But I lose voltage when the red from post X, the black from post 15 or the starter is energised. Also when i touch the thin red wire that I think goes to the voltmeter.

I have the Haynes manual, and I've been using the Pelican diagrams as well.

As I said, when I first tried to start it a week ago I had these symptoms, then I fidlled with the ig switch and it worked, started and ran fine, all the instruments worked. I turned it off, ran it again a day later, and then when I tried the other day - nothing. I have now put in the new, simpler switch to replace the ignition, and I tested the switch and can see it works.

It has to be a short somewhere, but why does every wire I connect cause the problem. Surely only one should?

[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,

[richardL]

I tried connecting directly from the kill switch to the yellow input to the starter solenoid and it turned over. When I tried shorting from the red power at the ig switch to the starter - nothing. So I jumpered a wire from the kill switch and touched it to the starter post of the ig switch and it cranked. Similarly when I touched it to the thin red out wire I got a good voltage reading on the volt meter (instrument gauge).

So the problem appears to be between the kill switch post to the ignition switch on the input power side - any kind of load is making the resistence really high (which I don't understand).

Any how I am going to get some suitable gauge wire and replace that power wire and hopefully I will be back in business.

We'll see...

Richard

[Dr Evil]

Short, and has to be with something common. If your meter drops to 0V that means that the place that you are testing from and ground have the same electrical potential (they are electrically the same point).Next is to find where these wires are together. I suspect that the wires have been altered by the DAPO.

[richardL]

The new wire cured it - fired right up (IMG:style_emoticons/default/smilie_pokal.gif)

Only briefly though as the fuel pump is powered off the accessory circuit and I hadn't connected that.

So... connect that up and then plumb the wire into place correctly and I should be in better shape.

Thanks for the help.

Richard

[David_S]

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.

This is what I was thinking also......broken wire, not shorted. Sounds like the wire is broken or not making a full connection at one of the terminals. I have seen this exact thing where a wire will have about 30 strands of wire and all but 2 or 3 strands are broken. The wire will carry 12 volts until you put a load on it and then it can't carry the amperage, so the voltage drops to 0. Could be wrong, but this is what I am guessing!

DavidS