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 a 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.

[Forrest]

The speedometer/odometer not working or working erratically is probably one of the most common problems on a Volvo of that vintage. There is quite a lot of information in the FAQ worth looking at, for example:

https://www.volvoclub.org.uk/faq/Ele...eterRepair.htm

But have a browse from:

https://www.volvoclub.org.uk/faq/FAQSummary1.html

The wires wearing out near the sensor is a common problem but also the electrical problems behind the dash described in that first link.

Does your car have a rheostat to adjust the brightness of the dash bulbs? Is it in the bright position? If so, does it have voltage either side of it? They can go faulty and be the cause of illumination problems. As can loose solder joints on the dash PCB.

Is the illumination on the centre console and elsewhere working?

[ConCon]

The dash does have a rheostat and I've tried adjusting it with no success. If you're referring to the center console as in the stereo and cigarette lighter etc, it has a cheap aftermarket stereo that works but has no illumination. I took the whole dash apart and it looked like there was a plug that was supposed to plug into the stereo but this current one didn't have a port for. I plan on changing the stereo soon. There are no other lights on that portion (not sure of the climate control is supposed to have lights or not, of so it doesn't work). The lights for the seat warmers turn on and I believe there is a light for the shifter but that doesn't turn on, might just need a new bulb.

I'm hoping that the instrument panel is just a sauldering issue as that won't be a difficult fix. I have not checked if the rheostat has voltage on either side as I don't know how, nor do I have the proper equipment I don't think.

Most all of the rest of the lights work (the warning lights at the bottom of the instrument panel I mentioned previously). The overhead dome light partially works but I'm pretty sure it's because of the whole fixture. It was taped on previously and I took it off today to inspect it. The big light works barely but the two lights in front do not. The headliner is rough and there was a lot of insulation dust on the whole circuit board so I assume it's just really dirty (I wasn't able to clean it). I will be replacing the whole fixture soon.

[ConCon]

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

[bob12]

Have a look at Dave Barton's website where there is very useful stuff about speedos and fixing their problems.

https://www.prancingmoose.com/740-odometer-repair.html

The speedo will not move when you turn the car on only once moving.

The plug behind the radio head unit is probably the fly wire for the original amplifier which was fitted to these cars as the original units didn't have a decent power output. It is not necessary with modern units as long as special by-pass wiring is fitted to link the speakers up at the old amplifier.

Bob

[ConCon]

Update:

I bypassed the rheostat dimmer after testing that it had no voltage and the gauge lights still didn't work. I'm guessing there's a problem deeper in the circuit board of the instrument panel which I plan on inspecting more tomorrow