My speedo is acting crazy. I shift from Park to Reverse and the speedo dial jumps from 0 to maximum and back to 0. It jumps around crazily while reversing. When I put it into Drive and go forward the speedo jumps around and kind of settles down yet indicates speeds that are much faster than reality. For example on a 35MPH street with other traffic to compare to my speedo indicates about 80MPH. Also, the odometer no longer works and failed about the same time the speedo went crazy.

Replaced speed sensor on AT and no improvement.

Took the instrument cluster out and inspected the PCB (printed circut board) and wire connectors attached to it. Ohm meter indicates all the wire traces terminate at the right points. There is a 11 wire connector from the firewall to the PCB. I traced all the 11 wires to various points on the PCB. Some wires feed the turn signal indicators, bright light indicator, temp gauge, fuel guage etc. 3 wires connected to three traces that led to the speedo/odo gauge. One wire look like a ground. I assume the other two
wires are for the speedo and odometer. One is colored white-orange and the other was blue-white.

I attached patch wires to these 2 so I could assemble the cluster yet have thes patch wires accessable to my volt-ohm meter. I want to measure the resistance and voltage on these 2 wires when the van was moving.

Here is what I saw.

1. White-orange. Moving the van very slowly forward the voltmeter shows the voltage toggles between 0VDC and 5VDC. When the voltage drops from 5VDC to 0VDC the speedo dial jumps from 0 to ~70MPH. Sometimes the dial does not move at all. Given the wire voltage behavior and speedo dial behavior are correlated I believe the white-orange wire is connected to the speedo.

2. Blue-white. With ignition on, this wire reads a constant 12VDC. With the engine running it reads a constant 15VDC. Unlike the White-orange wire I didn't see this one toggle. I assume the blue-white wire drives the odometer.

Quesions.
1. Is the white-orange wire the one to drive the speedo?
2. What electrical signal should I see on the white-orange wire? Is the behavior above correct?
3. Is the blue-white wire the one to drive the odo?
4. What electrical signal should I see on the blue-white wire?



BTW. I found another article on the web that stated the following.

If you have a DVM, set it on OHMS, connect the leads to the electrical pins, and manually spin the rotor. the ohms should read 1,0,1,0,1 ect as you spin it. About 12 times per revolution.


On some dash clusters (especially high mileage vehicles) the electrical contact pins that are inserted into the circuit board get loose. Use a 25W soldering iron and run a bead of solder around the base of each pin to restore the connection to each foil tracer on the board.


Thanks in advance,
William