1994 xj40 Speedometer not working after replacing heater motor²

Hi to all,
I replaced the driver side heater/ac box because the fan motor was dead. Now the fan works fine but I lost my speedometer and odometer. On the
plus side, I now have the backlight for the odometer working which didn’t work before.
I suspect this is an electrical issue, unrelated to the heater, caused by disturbing some extranious wire or wires.
If anyone can offer any suggestions as to what wires to check, and/or how the speedometer/odometer is wired, I would be greatly appreciative.
As always, thanks in advance for any and all replys.

Gary, the road speed signal comes from the four wheel sensors, through the ABS ECU (in the trunk on the left wheel arch), which sends a varying AC voltage signal to the instrument pack. A green/pink wire to pin 15 of connector LB21, a black 24 pin connector that plugs into the back of the instrument pack, carries the signal.

Thanks Mike for that information. There are no wheel sensors on mr car. They were broken off when I purchased the car. The vcm has always displayed the antilock warning light, but the speedometer and odometer has always worked until the fan was replaced. No work was done in the trunk except to remove the battery cable.
That being said, there is nothing to prevent the ecu you mentioned from expiring in its own time, so I will look at it also.

The plug at the back of the binnacle has probably been dislodged, check that - seems the most likely if you were working up in that area.

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Gary, if there are NO wheel sensors on your car I am hard pressed to see how your speedometer and odometer were working. I found this post in the archives: [xj40] '93 - '94 Speedometer & Tachometer Input Signal Sensor Source .

I do not know exactly how the wiring to the aforementioned connector LB21 is routed - the “LB” indicates left bulkhead - but my guess is either that green/pink wire has been damaged or, as abercanadian (Larry) suggested, the connector has been disturbed.

I will check the the right front speed sensor. All I know for sure is that the speedometer and odometer worked last week and do not work now. What broke the odometer fixed the backlight. The only area touched by human hands was under the dashboard; left side to replace the drivers fan and right side to apply 12v to the passenger’s fan, which failed the test.

Is there only one wire feeding both the speedo and odometer from the ecu in the trunk?

If the speedo and odometer were working fine before you pulled the blower motor it’s more likely you have disturbed a connection rather than something else has failed. First thing I’d check would be all the plugs and connections to the rear of the instrument panel, unplugging and checking where each wire enters the plug to see if it’s been inadvertently strained or pulled.

Yes. Here is the I/O table for the instrument pack:

And a snip of the wiring diagram: