Speedo issue

[KEVORM]

Got my car running today, its an 84e with an M20B25 and '89 harness. Tach works great but when the key is placed in the on position (1) the speedo goes straight to 80mph or so, then when the car is started it goes to 135mph or so and stays there. Any ideas? Only the blue and white plugs are in the back of the cluster. Thanks in advance.

-Kevin

[jlevie]

That sounds like a bad speedometer.

[Gregs///M]

Yup, most likely failed speedometer. I have a few extra if you need for the older clusters.

[James Crivellone]

Kevin that sounds like a bad cluster mainboard. Possibly a trace that is shorting to another.

I know you probably did the wiring correctly so I won't even go down that road of diagnoses. The speedometer circuit it pretty simple, 2 wires that go to a reed sensor in the diff. Very simple circuit.

If you can (or have not already) replace the cluster with a late model one (1 red SI light + Coding Plug) versus the unreliable early models (3 RED SI Lights, weird stick looking coding plug on the rear of the tachometer)

--James

[seatown88]

Kevin that sounds like a bad cluster mainboard. Possibly a trace that is shorting to another.

I know you probably did the wiring correctly so I won't even go down that road of diagnoses. The speedometer circuit it pretty simple, 2 wires that go to a reed sensor in the diff. Very simple circuit.

If you can (or have not already) replace the cluster with a late model one (1 red SI light + Coding Plug) versus the unreliable early models (3 RED SI Lights, weird stick looking coding plug on the rear of the tachometer)

--James

Is it a direct swap?

I'll try this for Kevin over the weekend and confirm a failed cluster or not. Thanks for all the input everyone!

[Pipes]

What's the cutoff on early vs late? Can I put in a VDO cluster on my '91 if I started with a Motometer?

[Gregs///M]

Cut off is 1986. VDO and Motometer are interchangeable.