Tampa 928s

78
Switch was replaced before I received this car you have to turn it several times till the starter engages it is hit or miss and has not worked the last several times. The switch was modified with a different arm from what I was told. The alternator was not charging, lamp is on at start-up and stays on, no voltage present at D+ pin 1 of 14 pin or 08 of CE panel. I have been starting the car with a power probe on the A2 of the Ce panel for convenience while working on various things.
I used a 3 Watt bulb from D + to power, it light started the car and it was charging. Looking at the circuit diagrams it is not clear if in the start mode 50 the voltage should be present on D+. Does it turn on only in start position or is it powered all the time via bus 15? My thought is that the switch enables D+ and by not using the switch but using the power probe some circuits are not being energized.
If the new switch is bad anyone know about the later switch with early arm changes?

Mrmerlin

with this issue it sounds like it could be a problem with the 14 pin connector under the hood.
since the charge and the start go through here thats where I would look first,
for shedding insulation or damaged wires

Tampa 928s

The 14 pin is clean and continuity was verified all the way back to the CE panel. The odd part is that the lamp is on on startup but no voltage to D+. The only other possibility is a ground short on the exciter circuit any confirmation on the voltage on startup requirement?

Tampa 928s

Checking the 50 circuit off of the switch I have no voltage when turned to start. Also no voltage when checking the jumper on Xv relay this is a manual. This is a new switch from Porsche 964-613-1200 but I heard there is a cam change for this year to get this switch to work anyone know about this? I can start the car with the power probe using A6.

Tampa 928s

On the back of the cluster located in the speedo area I found a narrow spade connector but no wire to connect to it. Is this a possible ground wire?

Alan

The exciter wire is powered by ignition bus (15) via the bulb...

Is the ignition switch diffrent for a '78?

Many switches floating around (eBay etc) are poor quality knock off's - get an OEM replacement from a good source as a starting point here.

Alan

Tampa 928s

I located a good switch from my 85 car now starts but alternator is still not charging.
I have voltage on CE panel h7 tested to the bulb 8r from the cluster connection.
I have 1.7 volts off of 9r from the cluster connector from bulb but no voltage to H8 and o8.
I verified continuity from D+ to 9r wiring is good.
I see VIII/15 on the current diagram but not sure where or what this goes too.
The odd part is that bulb stays on all the time including when key is in run position, a ton of wires added including a electric door mod so do I need to trace VIII/15 if so where do I start?

Tampa 928s

After thought; when I received this car it had this problem I had the alternator tested is came up bad. I replaced it with the same type Remy 13122 I do not have a resistor on the pod could this be the issue. With a 3-watt bulb connected directly to D+ it charges.