Speedo problems

[Fred_M1010]

Today I tried to help a friend to fix his completely dead speedo in his W250 -93 (CTD of course )
We swapped over both the sender unit (with gears and everything) and the instrument panel from my truck, but it was still dead.
We also measured that there was a connection between the black/blue wire at the sender, and to the ECM.
And that the white/orange wire were connected to both the ECM and the instrument panel.

The black/blue wire was 0V and the white/orange was 5V with the ignition on.

Any ideas?

How does it measure the speed, is it an analog signal or pulses from the sensor?

Can the neutral switch or the 4wd switch have anything to do with this?
(both of them are disconnected, due to some electrical problems...)

He's got a manual NV-trans btw...

[ellis93]

You should ohm the wires out from the sending unit to the computer to make sure that the both wire have continuity, now broken spots. My moneys on a broke wire since you've swaped in your stuff.

[Fred_M1010]

We also measured that there was a connection between the black/blue wire at the sender, and to the ECM.
And that the white/orange wire were connected to both the ECM and the instrument panel.

Done that
But my english isn't the best so maybe I expressed myself poorly...

Could it be a broken ECM?
What else does the ECM govern?

[ellis93]

Your english is fine, I just didn't retain the whole post

[Fred_M1010]

I think we burned up the speed sensor
Because now when I swapped everything back to my truck, my speedo doesn't work

He did attach it to the wrong wire at first, and I'm guessing it was a 12V wire...
And since my OD doesn't work I guessed it must be the sensor or the little gear box.
If it was in the dash, the OD would probably still work I think...

The gear box seemed to work fine though,
and the gear inside the t-case also seemed to be ok,
since it rotated when I jacked up the rear axle and turned the drive shaft by hand.

So out of curiosity i disassembled the sensor, and I could easily tell it was broken when I had it apart.