I have installed an aftermarket VDO speedo to replace the cable driven one. the background is i have a 96 xr8 and 4 speedo auto in a 67 mustang. I noticed the other day when the car is stationary the speedo needle jumps up to 2o mph! I have the falcon instrument cluster with speedo hidden behind the dash. I can't connect the speedo to the wiring after the instrument cluster as it is changed to a signal the speedo does not recognise. Could the speedo being connected interfere with the vss signal? Also how does the TCM get what gear the car is in ie 1-2-3-D? via the DOL on pin 43?
I have the correct voltages at pin 58 for each respective gear position.

any ideas?

Hey -

I have the same problem with a bloody VDO signal convertor where my speedo needle jumps all over the place when my car is stationary. Have spoken to some people who specialize in instrument displays and speedo calibrations etc and the general concensus I get is that the VDO signal convertor is no good. I have a new signal convertor 'box' (which I have yet to install) which I've been assured will correct the problem. Basically, throw the VDO signal convertor away. If you live in Perth, I can pass the details of the company I have purchased my signal convertor box from.

Hope this helps.