Our 850's instrument panel lights were all out. I got my hands on the wiring diagram and wanted to share how to trouble shoot the problem:

Check fuse #35 - 10 amp. If that is good, chances are it's either the dimmer switch/rheostat (probable) or a wiring problem (less likely).

Pry the fog switch & dimmer switch out with a small screw driver - they pop right out.

Unplug the dimmer connector. There are five wires at the following pin locations:
1. BRN/ORG: Supply voltage with ignition at ACC or RUN.
2. BLK: Ground. (for dimmer - lights are grounded separately)
3. WHT: Supply voltage with headlight switch OFF.
4. PNK: Output voltage to lights.
5. WHT/BLK: Ground with headlight switch OFF.

Using your multimeter, check for correct electrical functions at the connector pins.

Jumper pins 1-4 (BWN/ORG to PNK). If the dash lights are now on with the ignition to ACC or RUN, it's definitely the dimmer. It can be left this way until you get a replacement dimmer.

Hope this helps somebody. Jim

 

Thanks Jim! This is good info, and your methodology is the right way to diagnose electrical circuits; essentially trace the pwr through the circuit and find where it stops; good job!

Vote for sticky!

 

I added it to the frequently used thread which is a sticky at the top.

 

Thanks Jim for posting this. About to conduct surgery for the same problem.

Just wanted to clarify the wire numbering; from Volvo's elect diagrams they have
1 Brn/org...in from fuse 35
2 Blk...ground
3 Wht...off from lights
4 Pnk...and showing this going to lights
5 wht/blk...

Just need to check how it is when I get the pliug out but in my case it looks like I need to jump 1-4 to bypass the rheostat.

In my failure case, the inst lights go on when I start the car, then go off a second or so later. Ignition switch all tested OK so I imagine it is something decayed in the solid state part of the rheostat; no rheo position will make it work. Just curious as to why the lights illuminate as the car is started.

 

Just took the rheostat out of the panel. Mine is the l-r slide switch type. Made by ALPS Japan. (now who said beware of Euro electrics...?)

Wires in switch are as per wiring diagram (see my post, above). So Ijumped 1-4 & lights work again.

I will get a new rheo tomorrow.

Thanks to Jim for starting this very useful thread.

 

Edit: I looked at another diagram and it showed pin locations as jrc indicated, so I edited the first post accordingly. The important thing that the BRN/ORG wire is jumpered to the PNK wire.

Strange how your lights would come on & go off - mine were dead as a doornail. I have a replacement dimmer but haven't put it in yet - it works just fine jumpered.

I'm glad you found my info useful. Jim

 

Thanks Jim

Actually it was 1-4, and it was brg/org to pnk that I jumpered.

So it looks like UK cars (where I got the wiring diagram from ...UK Volvo club, and Aussie cars, are wired differently to USA cars. No big deal.

Incidentally I went to my friend George at All European Japanese at Smithfield in Western Sydney (NSW members please note) who I believe is the most helpful source of used / 2nd hand parts in Sydney, and he gave me 1,then a 2nd, then a 3rd rheostat unit to try out...the third one worked and now ALL is good.

Conclusions:

1. it was the rheostat that was broken
2. looks like this rheostat is not a very reliable piece of kit
3. creationism is truly dead - there are mutant volvos out there

 

I agree these dimmers are a POS. I bought a used one that supposedly worked when the car was totalled. I wouldn't even bother replacing it if this one doesn't work - I like it jumpered.

 

I followed the above info as far as jumping the brn/org wire to the pink wire and dash lights came on, so I ordered a new reostat from volvo installed it and dash lights did not come on, so I called volvo and had them order another reostat and tonight I installed it and got same problem dash lights will not work, I rejumped the wires and the dash lights work........any ideas why it will not work with the reostat???? BTW this is on a 1999 c70 convertable

 

Ron,

There must be an issue with one of the other leads (# 2, 3 or 5) to the rheostat and those need to be chased down. Otherwise, leave it jumpered and call it a day. Good luck!

 

Thanks Jim I will just leave it jumped and press on, thanks for the reply.

 

My Volvo 1996 850 GLT dash lights went out to. The rheostat was replaced and the headlight switch was checked to work. The fuse kept blowing out with and without the rheostat bypassed. It was the wire harness that was causing the problem. A wire tie on the harness was chafing the wires to tight and binding the wires too much causing discontinuity (breaking the internal wire strands). So I cut the wire tie off and bent the wires straight and used electrical tape to replace the wire tie. I also replaced the bulbs in the VDO console and inspected the PC Board. Now the general lighting for the dash for the fuel gauge, temperature gage, speeded and rpm gauges work. about 20 min later the dash lights faded out but toggling the rheostat slider turned the lights back on.

The harnes was also rubbing up against the car chassis but could not see where but the electrical tape solved the problem.

Thanks to all for the info!

 

Hi gents i now have this fault with my 850 and when i jump pins 1+4 and the fuse blows but with out jumping the fuse is ok lexworth which part of your harness was at faults thanks

 

Same problem, did you ever figure this out? Looks like I have ground on PIN 4 Pink wires all the time.