How can I test a speedo sensor on 915 box?
 

Hello,
My speedo doesn't work (didn't since I got the car last year - must likely because of a re-wiring botchjob before). The speedo itself is new and I am tracing the wires to check them.

Anyone know how I can check the actual electronic speedo sensor that mounts on the side of the 915 gearbox?
i.e. Ohms across it, etc.

Thanks for your help!
BRD

Just put the meter set to Ohms across the 2 leads in the tunnel, as you rotate the wheel you will see it pulse.

Ahhh... perfect. Thanks!!

need sensor i have a good used one

Just checked the sensor... all fine there. Am checking the wiring on the speedo now.
You happen to know which wires go where?
I have two speedos... a 260kph one (I think) and a 300kph one. They have different pins being used on the back.
The 300 one has +, 2 (not used), A, 31b, -
The 260 one has +, 2 , A (not used), 31b, -

I'm guessing the two signal cables go to 2 or A and 31b.... and other two are power and ground?

I am actually not sure which one is the right one... 260 one was in car (it's new), but never worked - which I'd blame on bodgy wiring that I have been fixing these last months.

Thanks for your help!!!
brd.

Just a hint, but info on the car and engine helps when asking questions.
Here is a pic I found doing a search.
12V power goes to the top+ terminal, ground and one lead of the speed sensor goes to the
bottom - terminal, and the other leg of the speed sensor goes to the
31b terminal.
http://forums.pelicanparts.com/uploa...1280690448.jpg

Your completely right Ed.... Its an 81 SC engine with 915 box in a 1970 911T... and the existing wiring is a repair job... which I tried to do right with the correct colours etc... but prefered to work with the connector references on the back of the speedo. I found that post too with that pic... followed it... found the SC wiring diagram (also here on fabulous Pelican) and saw the little detail that sorted everything: One of the speedo sensor cables has to go to that ground pin on the back of the clock with a spade splitter connector. The second goes to 31b... then add 12v to + pin... and rock n roll!!!
I'll check thats its reading right enough next time out with a TomTom.

Thanks for everyones help... again! :)
BRD