89 740 GL Wagon instrument/speedometer/odometer need help

[ConCon]

Hello all, I recently got a 1989 740 GL Wagon. It needs some work done to it but otherwise, it's in fairly decent condition. However, I was informed by the seller that the speedometer and odometer weren't working. He had a sheet with some of the possible issues and told me that the mechanic said the sensor on the drive shaft just needed to be tightened. I didn't think it was a big deal, should be an easy fix right. Wrong. When driving it home it got dark and I realized the lights for the instrument panel also weren't working. The warning lights (check engine, service, parking brake, brights, etc) all worked fine but I couldn't see the gauges. I changed all the bulbs and fuses and still nothing. Going back to the sensor, I took it off (after some difficulty getting the original Allen key bolt off) cleaned it some, and plugged it back in. (I'll also add that it didn't look like it was plugged in all the way originally.) The wires look a little rough with some electrical tape wrapped around one with the exposed wires.

Is this a common issue and just needs the ABS sensor replaced? Or is it the wires?

For the instrument cluster lights, could this be related to the sensor not working?

I'll also add that upon research, I found the lights could be because of a bad day running lamp fuses so I changed that only to find there was nothing connected to that fuse slot. It seems the day-running lamps still work regardless though.

Any help would be greatly appreciated, thank you.

[ConCon]

I'll also add that the speedometer doesn't budge when I turn the car on

[volvolugnut]

You mention ABS and speedometer problem together. I may be wrong, but I think these are separate sensors. I think the ABS sensors are on the wheel tone rings and the speedometer sensor is at the differential. Perhaps the speedometer does get a combined signal from both rear wheels from the tone rings.
This thread has a pdf with 740 ABS system wiring info.
viewtopic.php?t=30561

volvolugnut

[ConCon]

I'm specifically referring to the one on the differential. I've seen some people refer to it as the ABS speed sensor. I apologize for any confusion

[1990Volvo740]

What were the tool sizes that you used for pulling the instrument cluster?
I have a 1990 aand want to do the same.