I have a '97 850 wagon and I think this problem started a while ago (at least I think this is related to my current problem). It started a while ago with the light on the dash coming on when you use brakes (indicated burned out bulb, right)it was just the center brake light and it is a "beater" car so I didn't bother with it. Then the dashlight started to flicker on and off when pushing brakes and sometimes not coming on at all. Now most of the time when I use the brakes the light does not come on anymore and now none of my brake lights work. Actually the warning does still come on once in a while and I think when it does come on my brake lights (except center one) are working. Any ideas???

 

Check for a loose connection at the brake light swith. It is a plunger type switch by the brake pedaland should have two wires connected to it. If that is ok, check the fuse.

 

I will bet the brake light switch is bad.

 

I'm sure if I had a repair manual this would be much easier, but I did some testing/checking with a mulitmeter and these are my results:

Fuse is good
Bulbs appear to be good (work in the turn signal socket)
No visible corrosion in light sockets
Brake lights actually came on once or twice during testing

I found 2 switches on the brake pedal. The lower(closest to floor)switch has 4 wires: red, yellow(assuming is grnd), blue/yellow stripe, and green. The upper switch has 2 wires: grey(assuming grnd) and grey/white stripe.
Lower Switch Testing:
Ignition off: 12v between yellow & red
Ignition on: 12v between yellow & red, 12v between yellow & blue/yellow stripe
Ignition on/pushing brake pedal: 12v between yellow & red, 12v between yellow & blue/yellow stripe, 12v between yellow & green
Upper Switch Testing:
Ignition off: nothing
Ignition on: nothing
Ignition on/pushing brake pedal: 12v between grey & grey/white stripe

Hopefully this will give more information for a better conclusion as to what the problem may be. Thank you very much.

 

Download the 850 Service Manual and save it to your desktop or someplace else.
http://www.matthewsvolvosite.com/cha...pic.php?t=8018

Owners Manual
http://new.volvocars.com/ownersdocs/...0/94850_1.html

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Which one had a vacuum hose to it?
I believe the 4 wire one is the correct one for the brake lights.
The one with the hose is for the cruise control.

Does the shiftlock work?
Also the bulb failure relay should be under the panels in the L/R of the car. It is a Blue relay.

 

I didn't see a vacuum hose on either one. What does the shiftlock do? I don't know if it works. What does the bulb failure relay do?

 

I looked in the owners manualabout the shiftlock and I'm pretty sure it works. I cannot shift the car from park unless I am pushing the brake pedal.

 

OK if the shift lock works atleast half the switch works.
The relay is what tells the light on the dash a bulb is out.

I have seen a few relays go bad and cause the same problem.

 

So the relay can cause the brake lights not to work? I'm not using the warning light on the dash to tell if the lights are working, I am actually looking at the lights. How do you check a relay? Thank you.

 

You would have to test at the relay in the back and check for power going it and coming out.
I checked my wiring diagram but cannot find the brake light circuit in it.

 

Ok, I found the relay. Using the wiring diagrams from the repair manual in the line posted by "Quick Brick" I was able to determing which wires on the relay were for the brakes and anything related.

During testing I had the ignition on with car off and 2x4 on brake pedal. At time of testing I had no power coming from the brake light switch and no power the of course for any of the lights. Then I stopped testing to check something in the diagram. When I resumed testing the brake lights were working again and I had power coming from brake light switch at the relay. I then started playing with the pedal. Holding it on longer, pushing and releasing quickly, etc. It seems that sometimes (rarely) they come on right away but most times you have to hold the pedal for a while before the comeon and of course sometimes they do not come on at all. I am thinking there is some kind of "short" or problem with the switch but not sure.

Another thing maybe I should have mentioned earlier, I do know the center high mount brake light is burned out and has been for a while (just a beater back and forth to work so I didn't bother spending the money on a bulb). Anyway I am wondering if the connection for that light is corroded could it cause the whole brake light system to malfunction or "short"?

What do you guys think? Thank you.

 

Brake light switch is bad. I am 99.9% sure that is the problem.

 

Thank you, I will order one and see what happens.

 

Let me know how you make out.

 

I will definitely post what happens.

 

Thank you to all who posted comments/advice. I ordered a stop light switch from FCP Groton, which even with shipping (cheapest option) was cheaper than my nearest Volvo dealer. I installed the switch and the brake lights seem to be working properly. So it looks like problem solved.

 

Glad it is fixed.

 

Hi,

I've just been informed that I have no brake lights. I haven't driven the volvo much lately but the last few times I have had to use the shiftlock button to get it out of park. Will a new switch solve both? How are they related?

 

I have to install a new Stop Lights Switch(Brake Light Switch) to get my rear brakes lights to work...How long should this take and any tips for doing so