I have been trying to find out why, after replacing the broken gears on the odometer, it still doesn't work; Neither does the speedometer. I've tried 3 used speed sensors, but still no odometer movement. (I can still find the true mileage using the on board computer, so that is a plus.) Is there a wiring schematic available that explains where the power comes from that feeds the odometer and speedometer? and is that power 12 volts or something less? Also what power source turns the odometer motor and what "appliance" converts the speed sensor signal into voltage? Thanks.

 

Found this:

The signal to the speedo is generated by the front wheel speed sensors and passed thru the ABS module to the cluster. The wiring internal the ABS modules is problematic. Try wiggling the wires leading into the ABS module and pressing in lightly on the plastic housing. This will a lot of times create a good contact and the speedo will function if that is the issue. A scan tool that is Volvo capable is really the only way to diagnose beyond the obvious.

If its a VDO cluster and the diagnostic plug underhood with the LED a test goes like this: Do a function test. At the A/B box, place the jumper lead into A:7. Turn the key on. Press the button 3 times. Look at the instrument cluster. The fuel gauge should now be at 1/2 tank, temperature gauge should be on red, speedometer needle should be vertical, tachometer should be vertical.

PS - I have a spare cluster from a 95 850T if you'd like to test by swapping out...

 

OK. Thanks very much. I will do the function test Saturday. I tried a cluster from a '95 non-turbo but it had a four wire connector going to the odometer, whereas my '94 cluster has only two wires. I tried it anyway but neither the speedometer nor the odometer worked even though it had good gears. Does your cluster have the two wire or the four wire connector? I'll try wiggling the wires also.

 

Also, I replaced the right side CV axle a few days ago so the sensor wheels are both clean now and should work better than the oily/greasy one I replaced.

 

Update: I did the function diagnostic test. The speedometer and rpm gauge needles pointed up. The odometer ran up about a half mile and stopped. I guess that means the basic cluster is working. I cleaned up the rubber-turned-to-tar on the relay pins next to the ABS computer; took it for a test drive but still no odometer movement. I'm not sure what plastic cover you referred to but I un-hooked re-hooked the ABS computer a few times. Even tried a used relay from a pull a part car (the one by the ABS computer); no change. I may try removing the ABS computer and see if I can make something happen there. (an aside: I read a post that mentioned that the newer 850s odometer/speedometer information did pass through the ABS, but for the older ones, did not.)