I need help with a Speedo problem on a 1976 911
 

Hello everyone.

A little background first. I have a 1976 911 that I did a 3.0 motor swap on. Everything works fine besides speedo.

The speedo works fine until you turn on the headlights. Then the speedo goes to zero. I have no idea why. Once again , driving during the day without headlights, speedo works perfectly , then when you turn on the headlights. Blammo, the speedo stops working and indicates zero with no movement.

Any help would be much appreciated.

Cheers,

Darren E Hall
TEL: 406-471-5883
email: ffsportacarmg@hotmail.com

1963 356B Coupe
1967 Porsche 911 Coiupe
1968 porsche 911 COupe
1970 Porsche 911E coupe
1976 Porsche 911s

just guessing - i'd be looking for an accidental connection between the speedo signal wire and the ignition switch wire that goes to the light switch

get a good oem wiring diagram for both years cars - from factory manual is best - blow em up to table top size at Kinko's et al & follow the routing of all the wires now connected to it with an ohmmeter

i am dealing with a similar dash wiring problem and today i found a P.O. had connected several wires all together that should have been independent

, and that some patching had been done that resulted in "correct color" wire being attached downstream to a different color wire with a different purpose, and that "wrong wire" was connected to the light switch, shorting out the circuit every time the lights were turned on

- that can drive us nuts


good luck

ps - check this thread for ideas http://forums.pelicanparts.com/porsche-911-technical-forum/361429-1968-swb-turn-signal-park-lamp-operation.html

Check the ground on the speedo. A lot of these type of issues are bad grounds.