Got two responses to my last e-mail. This is great having help! I am in the process of buying this car from a relative.
The high mount brake light does not work, even with a good bulb. Looks like I need an electrical diagram. But, the Service Manuals listed on the Volvo site don't help me be sure of which to buy. I think it would be the one that just lists wiring diagrams. The numbers they show for 3 different electric manuals are:
TP 32127/2 TP 3501201 TP 3701201 Anybody know for sure? My guess would be a connector somewhere.
Also, the overhead switch in the center of the roof that controls interior lights appears to be broken, I can't move it. Any ideas as to best bet on replacing? Just order from a dealer?
Last question. I hear some knocking in front when driving. All I can find is that when you turn steering wheel back and forth a little I get some knock, and it is in the shafts going in to the steering rack. I imagine I need new tie rod ends on the interior end. Not sure how to be certain the struts are OK, but they seem to be.
At 123,000 miles, I think I better change the Timing belt too. And the darn SRS light is on, fault code is 222, someone here said that is Passenger AirBag, my guess is that I pull the glovebox and check for the wiring connector there.
Thanks for any advice. My nearest dealer is 70 miles away.

I have same problem on my high mount brake light. I've done everything possible: checked ground, fixture itself, juggle wires, replaced 3 different bulbs, and checked electrical diagram...it still goes on and off for no reason! It'll come on and stay on for a time, then go off for another... The other 2 brake lights that are connected work 100%. I'd like to know myself how to "fix" this light.

What would happen if you spliced into the hot wire to the brake light at the rear, and ran it to the high mount one? Surely the high mount would then light, but I haven't studied the electrical diagram enough yet to see if the darn dash light would still light indicating a lamp out when you put your foot on the brake.

I had my wife keep foot on pedal while checking with wires in light and nothing occurred. For the past 2 days, the light has been OK. According to the diagram, which I have, there's a connector to the brake lights on the left side of trunk. I tried cleaning them also. That hot wire idea might not be bad, if I get desperate! thanks

Be careful working around the air bag. A Volvo TSB I have seen
advises the techs to stand outside the car when pulling the glove
box (this is in a TSB for 98 models that required an extra ground
strap to prevent the bags from going off from static charges). Of
course, this is a TSB for the possibilty of the bag going off from
static and they are connecting a ground strap to the SRS module.
I have a subscription to alldata.com ($25 year) that allows
anyone to see the TSBs and content for their model (which is where
I saw this).

I think you should get the dealer to handle the SRS problem.
You are dealing with an explosive device that can really hurt you.
I would not be pulling on wires, thats for sure.

Also, look on drivers door for an expiration date for the air bags.
My 95 and 98 both say replace after 10 years. But, latest I have heard
from Volvo is they have extended this to 15 years (that was
posted on this board).

Thanks for the caution. I know the air conditioner was worked on in this car, and the glove box appears to have been pulled out as evidenced by many of the screw holes have no glove box material around them. So, I'm wondering if someone disconnected the wire to the passenger airbag while they were working as a safety, and forgot to replug it. Was going to pull the battery cable before I started. Actually, my first step was going to pull the bottom off the dash area under the glove box, to see if I could see up behind the glove box for a dangling connector!! The dealer is over 70 miles away, not real convenient when you are at work all week!!

Just a note: As I recall, on My 70 series I had to pull
the glove box to get at two screws behind it that secure
the lower panel (I had to replace the blower motor behind
the glove box). I'm not sure if the 850 is the same. In any
case, with the glove box out you can see the SRS system; I don't
think you could see it well with the glove box in place.

The hardest part about getting the glove box out was I had
to clean it out first (its an easy job to remove it).