hello everyone
I've been having trouble with my 1988 Volvo 240. this car was my daily driver back and forth from Modesto to Merced but then i had a short on my speedometer and so we tested the circuit board which was bad on a few components so i just bought a new circuit board and speedometer. now the speedometer doesn't work or my tach gauged and i know i have all the wires in the correct spot. i was driving the car without knowing how fast i was going but my car recently died so I thought alternator went bad so replaced that. the car worked but then lights kinda go dim and battery light is on now. i have a new battery so that's not the issue. i don't know if my speedometer sensor is bad or my hall sensor or even fuel pump relay. i just need help knowing and how to get to the bottom of this issue. i love my Volvo and i miss driving it.

 

Battery light is on because the alternator is not charging - specifically the voltage in the car is higher than the voltage coming out of the alternator.

"New speedo and circuit board" - did you mean used parts?

I seem to remember that in some 240's (it's been a while) the alternator will not charge if the instrument cluster is unplugged. The alternator needs the wire to the warning light to be connected to tell the alternator to charge.- So not sure what you have installed - but I bet they are not compatible with your car. How about just a whole used cluster - plug it in and see if it works?

 

pretty much ALL older cars, that ALT/BATT light is a key part of the charging circuit, it provides the D+ 'bootstrap' current to the alternator, without it, the alternator won't start charging.

 

i did buy a cluster circuit board and speedometer from pick n pull but i have been driving the car with the speedometer and tach wires unplugged because they don't work even when they are plugged and i don't want anything bad to happen to the speedometer or tach. any ideas why my tach and speedometer wont work. i thought it might be a speed sensor gone bad but i dont know and my tach not working due to hall sensor gone bad but still not sure yet.

 

if your hall sensor was bad, you would have no injection and no spark.

 

okay then i have no idea where else to check on why my tach and speedometer gauge not work. if anyone has any ideas where to begin this investigation please let me know.

 

those two devices are pretty independent. one counts ignition pulses from the #1 pin on the coil, and the other counts pulses from the speed sensor in the rear axle. they have a common ground at the instrument panel, and both circuits need power from the battery/alternator ...

I'd have to dig up the wiring diagram to get more specific. and its 10pm friday night.

 

thanks ill try to read a wiring diagram as well but im not the best at those yet

 

ok, my wiring diagram for the instrument cluster of a 1987-1988 240...

the speedometer has its own 3 pin connector, '233'. 233 pin 1 (blue) is the actual speedo signal from the sensor in the rear differential, 233 pin 2 (black) is ground and the negative signal (the rear sensor is on a 'twisted pair' so its ground and signal are 'differential', this is an electronics thing that reduces noise in low level signals like this), and 233 pin 3 (red/black) is power from directly from ignition switch pin 15

the tachometer has *its* own connectors, diagrams are a little confusing, but it looks like the tach signal is a white-red wire to single pin connector , and power/ground are black and red wires to another connector.

all the grounds end up on a screw on the left side of the transmission hump, under the carpet, just behind the bottom of the center console, and just forward of the shifter assembly.

 

[QUOTE=pierce;491835the speedometer has its own 3 pin connector, .
the tachometer has *its* own connectors, tach signal is a white-red wire to single pin connector , [/QUOTE]

I seem to remember an extra single wire from the harness behind the cluster that is not used - however when one of my techs would think it should be used and plug it into the available spade terminal on the back of the cluster - it would fry the speedo!

Yes I purchased a few extra speedos to replace the ones we fried.

 

This site mentions the extra wire/fried speedo problem

240 Temp Faker

 

thanks for the feedback. I've been busy with school and work but on my days off ill try looking for the ground and the speedometer sensor wires as well.

 

hello again
i looked at the ground and it was fine. i got the tach gauge to work because it was the gauge that was bad but now i just have to deal with the speedometer gauge but I'm thinking the sensor is bad because the wiring was good.

 

the speed pickup in the rear axle is a simple magnetic inductance pickup, these rarely fail unless something catastrophic happens to them. more likely is a broken wire

 

i have no idea where to look cuz the ground was okay and the wires to the sensor looked fine to

 

in my Volvo book it says if the speedometer doesn't work or the the odometer then the sensor is bad

 

Unless the speedo is bad - have you ever seen it working? Wasn't it a "good" used junkyard part? I don't think I have ever replaced a bad speedometer sensor in the differentials on any Volvo (240,740,940,960) - had to fix the wiring on many cars though.

 

The wiring for the sensor comes up through the same place where you can access the fuel sending unit. Trace the wire up through there and there is a connection in the trunk as well. Check out this link:

1989 Volvo 240 Speedometer Diagnostic

If your are into the electronics part of the speedometer, here is another link.

Electronic Speedometer Notes

 

okay ill get to that when i can and get back to you guys. i got a speedometer from pick n pull because mine shorted when i was driving like literally smoke was coming out of my cluster. when i took out the speedometer when circuit board on the side with the while was burned.

 

turns out one of the capacitors on the speedometer is no good that's why the speedometer doesn't work. its time to go haunting for another speedometer.