Speedometer Problem

[Porsche G.I]

Hello Everyone, I'm having a problem with my speedometer....this is what happens..as soon as I turn the key to the on position my speedo just jumps straight to the max speed on it. I have tried many things but I cant seem to be able to get it to work right. I've even replaced the sensor but it still doesnt work correctly..it does the same thing. Please help or my 911 might just become a garage queen for some time. My 911 is a 74' with an 83 SC 3.0 engine and tranny. there are many wires that just dont seem like in the right place..I need some help here folks. Thanks to everyone.


SPC Diaz
U.S ARMY
Ft.Bragg, NC

[DW SD]

can you check resistance across the wires between the gauge and the sender? You should be able to measure at the terminal which plugs into the gauge and to where they plug into the sender. IE are the wires broken somewhere?

Your speedo could be broken, too. I'm no expert.

[Porsche G.I]

Well I suppose I could check the terminals and see if theres something wrong inside. As far as the wires being broken I kinda thought of that before..therefore I ran secondary wires from the sensor but still to no avail, the wire schematics do show more wires connecting to the speedo but being that this is a 74 chassis and an 83 engine I dont know if the mileage counter is there..unless its refering to the odomoter in the speedo.

[OSI930]

I pulled this from a previous thread that discussed wiring on an SC speedometer.
+12V = Red/Black and Red/Blue

A = White/Red

31b = Brown/Red (goes to the green from the Speedo Sensor)

- = Brown, Brown/Red (goes to the Brown from the Speedo Sensor), and Green"

You might check the back of your speedometer and see how it is wired compared to the above. Also, check your speedometer sensor connection under the tunnel cover which is on the floor behind the shifter and e-brake and infront of the rear jump seats.