Hey all im new to the volvo scene just picked up a 1987 volvo 740 gle auto. My friend was gonna junk it, but i wanted to fix it so here i am. Replaced the tailshaft as it was shot, and replaced the heater core because it was leaking. There is one more problem that I for the life of me cannot figure out. When my running lights or headlights are turned on, i get no backlights to my gauge cluster nor to the climate control or the shifter. None of the gauges work and for some reason, the blinker lights stay solid and the highbeam light stays on, regardless if the highbeams are on or off. The funny thing is, after you drive the car with the heat on full blast for around 40-50 minutes, everything suddenly turns on and everything works. What do you guys think could be the problem here? I thought maybe it was the gauge cluster itself, but any input would be greatly appreciated! Driving at night and not knowing how fast your going is starting to get old! Thanks alot in advance
craig

Maybe try replaceing or taping on the bulb sensor relay.

where would this relay be located?
craig

Hi again Craig,

The bulb out sensor is in the main fuseblock behind the ashtray /left rear.
Its red and about the size of a beer can cut in half.
I can't see how that is involved with your problem though.

You can use the search engine to get lots of info about specific items,
Lots of good threads from before.

Look carefully for other things not working.

It seems that this is a grounding issue of some sort that involves multiple circuits that also goes away after the car gets heated up. I initially suspected a wireing problem but I think that wouldn't be affected by heat that much. Unless it was associated with an circuit board. So ... based on my somewhat limited knowledge I'd guess either the lamp sensor or gauge cluster. Thought I'd suggest the easiest one first. This seems like a really odd problem and often times odd problems have odd causes.

Found out something interesting on the way home. If i turn the dimmer all the way down, the speedo and tach start working. The speedo is around 8 mph slow and the tach is about 600rpm lower then what it should be . very strange
craig

It probably would be best to get a whole gauge cluster unit. It looks like yours has some sort of cracked solder joint or corrosion somewhere. It may help to take it out and go over it using a magnifying glass.

Does the gauge cluster work with the lights off?

Yes, when the lights are off, everything works fine.
craig

Does the radio also quit with the panel lights?

Do the tach and speedo work? or are they dead too?

Its a weird problem, It might be miswired from some radio installation.
if you see any dimestore series crimp lugs try pulling on them.

What voltage do you measure at the battery with the engine running?

See if you lose power to Fuse 21 when the lights quit.

You can try unplugging your turn signal/hazard switch and see what happens.
pry out the rubber piece in the center of the steering wheel and take off
the center nut and the steering wheel comes off easily... I dunno if you can
access that stuff w/o yanking the wheel.

If you get the cluster out you should see 12V at pin 8/2 (connector "a")
its the 12V to the dimmer rheostat.
Make sure that all the instrument connectors are firmly seated.

Bill

No tach and speedo both do not work when lights are on. What I fail to understand is why everything turns on after driving for 45 minutes or so with the heat on full blast. The radio works fine, and the wiring for the radio is good. Ill try and check the voltage and whatnot this week and ill let you know what i find? Any other ideas?
craig

Did you try wiggling the dimmer control....the little stem on the left side of the instrument cluster.

ach, that's still not gonna solve the other dead stuff....
maybe there's an instrument cluster connector loose

or maybe you disturbed the positive terminal block where the passengers right knee is on the side wall near the ECU (when you did the heater core job)
There's several heavy red +12V wires connected there, one of which feeds the
dash cluster. You need to get your meter out per previous post.

you might reseat the instrument cluster connectors....

Bill

Alright, ill see what i can find out tomorow
craig

Found out something interesting on the way home. If i turn the dimmer all the way down, the speedo and tach start working. The speedo is around 8 mph slow and the tach is about 600rpm lower then what it should be . very strange
craig

deja vu dept:
"...If you get the cluster out you should see 12V at pin 8/2 (connector "a")
its the 12V to the dimmer rheostat.
Make sure that all the instrument connectors are firmly seated."

Did you do this?

I have not gotten a chance yet, work has been calling me in early all week, but im off thursday and friday, so ill be doing this tomorow
craig