Hello dear Volvo friends!
I have a strange funny problem with my instrument cluster (Volvo 945, 1997) a problem that i don not know how to continue with at the moment. I might need instructions on how to find the culprit. To shortwire the problem is still to early.

Last September i got the yearly roadtest/check of my Volvo 945 approved. Though one big bulb in the instrument cluster was out, so they tipped me to chenge the rest too.
As i did, change them all 4x W5W and some W2,1x9,5d.
A few days later i was on the road and suddenly all the lighting went out, could not read my speed etc. the signal lights etc. worked fine.
Then i checked the bulbs but they were all fine, noticed i forgot to change some of the smaller bulbs at the headlight adjustment panel W2x4,6d.
Then i read something about the dimmer/rheostat, checked that but saw no burned out circuitry in the potmeter.
Then i read something about the relay on the back of the instrument cluster, got another one from the scrapyard, installed it
and the lighting was back on! but after half an hour the lighting was off again.
Another rheostat-relay i found at another scrapyard, also another complete instrument panel with a thermometer lcd display that had not turned black, changed the speedometer, changed the dimmer-rheostat-potmeter.
Instlled it and everything functioned in all its glory! happy times!
I drove with it for a week but last night the lighting went dark again. fortunately i had not put back the plastic cover under, there where the legs are. So i could feel while driving the back of the instrument cluster, i noticed the rheostat relay got really hot.
So.. what might the issue be.. short circuit somewhere? a failing bad relay again? wrong bulbs?
any suggestions where to go from here?

 

I don't remember any relay on the back of my 740/940 instrument panels... but my last one was a 92, and the 940 series was discontinued here after 1995.

 

it's a metal case with one screw in the middle. That small case/box has four legs with eyes which is screwed to the flexible plastic circuitboard on the backside of the instrument cluster. Relay i thought it to be if not, how would you call that metal box? Dimmer regulator case?
like here:

 

So you replaced the main board and all was well for a week? Then the same thing happened again?

I'd start with the bulbs you replaced as all was well prior to the change: make sure they are the right power. Then I'd not turn the power on the rheostat all the way up, keep it may be at 75%-- it's a good general idea to do that in all cases, then the bulbs supposedly last forever. All this assumes you getting a hold of another rheostat "box". Of course, as in all things electrical, the dreaded "short" is always a possibility but in this case, as your new set up lasted a whole week, a short would not be likely, more like a heat overload of some kind. I am a firm believer in not replacing things preemptively--new parts these days are of questionable Asian origins and I prefer an old Volvo OEM than new who knows what; of course shops will push the "new".

These are my thoughts, keeping in mind that my electrical skills are far below my mechanical ones.

 

And, there is only 1x purple/white wire connected to the connector on the back of the cluster at point D. in other volvo's i saw also a Yellow/white wire connected to point D.
what are these for? Might that be the problem of the short circuit/ overload that it misses the yellow/white wire?

 

I might be wrong, but I think thats related to the tachometer and cruise control.

my 940 wiring diagrams only cover up to MY 95

wait, no, D is the output from the speedometer, and goes to the cruise control. the wiring diagram for 95 shows it can be eitehr a violet-white wire or a green-orange, dunno why the difference.

 

Point D usually has one wire attached from the ones I've seen... There shouldn't much diff. between 1995 and '98, last year for the 940/S90.

 

95 was still a 'classic' 940, I'd thought I'd seen S/V90 style facelift 940s in aussie etc pix ? the 960 had significantly different cabling and such ... fuse and relay panel were quite different than the 940... no idea if the post-facelift 940s used the 960 style panels or what. we had a S90 facelift for a few years but not long enough that I'd ever done anything beyond oil changes to it.

 

Ok, re-soldered all the solder points, tightened all the screws and sanded some contact points. Gonna install it tomorrow morning in my volvo. Hope it makes a difference.
Im am not sure if it'll work because the same problem was when i had the previous cluster installed.

keep you posted.

 

Don't sand gold plated contacts on circuit boards and connectors, use a clean soft pink pencil eraser on them, that will remove any dull oxide without stripping off the very thin gold plating.

I'm wondering if you don't have a bad connection on one of the main plugs into the instrument panel, or your replacement reostat as bad as the original. I use DeOxit on those reostats, and on electric connections in general

 

The 940 stayed 940 until 1998, mercifully avoiding all the 960/S90 lumpy body cladding. The biggest difference in the world cars (outside of the US) was the the turbo diesel engine and sometines the M90 manual trans. I doubt their lectricals, instrument pods, etc. were changed at all.

 

Hi.

I don’t know if it will fix your problem with the relay box on instrument. But the 4 x w5w Bulbs you were talking aboute, is originally 3w and not 5w. If you havent fixed it allready, maybe this is worth a shot.

Vegard.

 

One of possible causes - thd thermal fuse on 'relay' pcb. When you disassemble it from instrument cluster and open metal cover, you will find there small pcb. Gently take it out, find fuse (black rectangular thd element) if it not conducts, lights will not go on. Fuse is 3A, 115 deg C, 250V. When installed bulbs excedes designed ratings components might get hot and thermal fuse will do its job. This is single use element, so it must be changed for new one.

 

Just wanted to say a quick THANK YOU for this info about what's in the grey box. I discovered the thermal fuse , which had in fact blown replaced it and restored the display lights! Yeh!
Martin