Speedometer problem

[Laird Scooby]

Originally Posted by Camillus

Hi Bob, Yes, you are correct. 3 wires going into the back of the instrument cluster, green/white coming from the speedo. sensor, brown??, and blue/green,??
Tommy.

Originally Posted by Camillus

Hi Dave, Thank you so much for your help and guidance. I'll try to locate that small black box and hopefully (fingers crossed) the problem is there and not in the sensor.
Tommy.

Tommy, if you've found the plug on the back of the speedo, you can tap in there with a pair of jumper wires to link your multimeter to the sensor. Brown is earth/0V, green/white is the signal from the sensor so you can link into those and drive until the speedo drops out. If the voltage on the meter drops at the same time, you'll know it's a sensor or wiring problem. If the sensor still provides a signal, look at the +ve blue-green supply to the speedo to see if that's dropping out.

If you've got a constant signal (except when you're stopped of course) and a constant power supply even when the speedo is dropping out then it points to the instrument itself.

[bob12]

Originally Posted by Camillus

Hi Bob, Yes, you are correct. 3 wires going into the back of the instrument cluster, green/white coming from the speedo. sensor, brown??, and blue/green,??
Tommy.

Sorry been otherwise engaged. The other 2 wires are, off the top of my head, the primary power inputs to the cluster. If you look at the blue circuity there you will see + and - signs. That's where I connected up a Yazaki voltmeter I had 'spare' into the VDO cluster.

Bob

[bob12]

Backboard at speedo fixing screws. To the left (raised white molding) is the actual speedo connection to the blue circuit on the backboard either by pcb tabs or pins depending on age.