914/6 strange electrical problem - It will not stop!

[911goran914]

Hi!

I have a strange electrical problem in my 914.

The car is built from a 72 euro 914 into 914/6 with a 70' 2.2 911 engine.

After I finished the car it run great. But when I try stop the engine with the ignition key nothing happened. When I pressed the brake pedal with the ignition off it stopped.... This was a bit strange but worked all right until now. Now the brake trick stopped working.

I tried to solve the mystery yesterday. When I turn off the ignition key when it runs the charging lamp starts to glow. Not much but i think it should not glow when the ignition is off. Since the car don't stop I suspect that something gives charging power to the power relay on the relay-board in the engine compartment when the car goes and that this causes the 3-Pin unit to always get Power as long as it runs.

I tried to unplug the alternator plug on the relay board and that solved the problem. Bud then i have no charging

Any suggestions?

[Dave at Pelican Parts]

Check the wiring on your rear turn signal buckets. Also check that you have the right type of bulb in each socket. If you put a single-filament bulb into a dual-filament socket, it will feed back power into circuits that should not have it in those circumstances. Dual-filament sockets have two metal prongs at the bottom; single-filament ones only have one.

In my case, my car would run as long as the left turn-signal was on. The "parking light" feature was feeding power back through the ignition switch circuits to power the ignition and run the motor. I started thinking if I had done anything to the left turn signals, and I remembered that I had replaced a bulb. Turned out to be the wrong bulb.

--DD

[patz]

Check that fuel pump quits at shut off.

[Tobra]

It is probably what Dave said. I have heard of weird problems from having the wrong lightbulb. Could have damaged the ignition switch, even protected by fuses it could get pretty hot.

My super beetle ignition switch was very similar, maybe even the same, as the 914. I had the ignition coil slip once, ground out and kill the car. Melted the ignition switch, key got extremely hot.

[904svo]

Try putting a 1N4001 diode in series with the gen lamp lead to stop feed back.
If its installed right the lamp will light when you turn on the key.

[911goran914]

Hi Guys

Still have the problem.

I have checked the bulbs, they are the correct ones mounted as they are supposed to.
I have checked the ground wires "everywhere", can not find something wrong.

The current situation is this:

The car starts and runs great. The charging bulb glows before i give it some throttle and it charges about 14 volts when it charges. The only thing that does not work is the tachometer, it does not work when the engine runs and the ignition is on.

The problems start when i turns of the ignition to stop the engine. It won't stop. The strange thing is that when the ignition is of the tachometer suddenly works fine with the correct RPM. When i unplug the black/purple wire (RPM signal) on the distributor the tachometer still works. The tachometer is of course a -6 tachometer from the 911T car the engine came from. I have tried to unplug the tachometer but the car still runs...

If i remove the charging bulb the car stops. But without the bulb mounted the alternator do not charge... The alternator is a bosch unit with external regulator (from the 914/4 relay board). The alternator is recently rebuild and checked by a pro and is ok.

This is the wiring diagram on the relay board:



I use the "I" plug for 12 volt through the power relay to the 3-pin CDI unit. The "III" is connected to ground that connects to 85 on the fuel pump relay. This is needed to start the fuel pump relay (i am not sure why, found this solution in this forum). If i disconnect the power supply from the "I" plug and jump it directly to the battery the cars runs/stops if i disconnect the cable but the tachometer etc still behave strange...

To me it seems like the RPM signal through the CDI box somehow is the problem. I think this goes "backwards" through the CDI unit and gives the needed volts to keep the power supply relay on the relay board switched on. And when that is switched on the fuel pump relay is on and keeps the engine running.

This is the wiring diagram for the 3-pin unit:



The wire connected to C at the CDI unit and 1 on the distributor gives the CDI unit RPM signal. Could the problem be the CDI?

The car has a Marelli distributor of this type:



It has new contacts, distributor cap, spark plug wires, spark plugs etc.

This is the electric diagrams i use, Pelican Parts - Porsche 914 Electrical Diagrams , my car is a 72`, the engine is form a 70´911T.

Anyone?

[Dave at Pelican Parts]

It sounds very plausible, but I don't know where to go from here. My thought is that the wiring to the CDI isn't exactly what it should be, but I don't know enough about the stock CDI setup to really say. You might see if the 911 board has anything to say on the matter?

--DD

[904svo]

Remove the blue wire off the gen lamp socket and see if the engine stops when the key turn off.
If it does, Put a 1N4001 diode is series with the blue lead to the gen light bulb, if its installed correctly the gen light will light with the key on and go out with the engine running.

[911goran914]

Originally Posted by 904svo

Remove the blue wire off the gen lamp socket and see if the engine stops when the key turn off.

If it does, Put a 1N4001 diode is series with the blue lead to the gen light bulb, if its installed correctly the gen light will light with the key on and go out with the engine running.

I have spent all day reading wiring diagrams. When I wired the engine to the car i had only a 1969 and a 1972 911 diagram. The 1970 is different... It need intermediate unit to ballast the rev counter! Mounted that now and the rev counter works fine. One problem solved

Going to a friend to get a diode now, hopes it will work!

[911goran914]

Problem solved I put a diode on the red/white wire on the charging bulb and everything works fine.

Thanx Dave and 904svo for good input, the pelicanparts forum saved me once again