I purchased a new taillight lens and bulb assembly to replace the cracked one on my 91 740T. I purchased brand new bulbs, installed them. Brake lights would not light up. I tried the other circuit board. Still, the brake bulbs did not light up. I can't imagine it being the fuse, because the turning bulb, and reverse bulbs work, which I beleive are on the same fuse. Any other suggestions to check out? I gotta get this thing inspected.

 

I've been having a problem like this with my '89 240 lately. One of the brakelights will periodically go out. It seems like its a problem with the connector that plugs into the circuit board. I can usually just unplug the connector, push the wires in a little, then plug it back in an it will work fine. Might not be the best advise, but its worked until I get the chance to dig deeper into the wiring. If both taillights arent out, you can wire the driver and passenger-side brake lights together to pass inspection. This is what I had to do with my reverse lights. Hopefully someone can give you a better answer.

 

If you can check for power from the Brake light switch. If you have power there and none in the back then the Bulb Failure sensor is bad.

 

Haven't broken out the multimeter yet. I'm not quite sure what you mean by the brake light switch though.

 

the brake light switch should be attached to the brake pedal assembly. there should be an adjustment screw on it, if you have power try turning the screw a little one way or the other. i now it worked on my honda, but im not sure about Volvo's. Tech will know if it is the same way im thinking.

 

You will havw to loosen the Nut to adjust it.
But I will bet the Bulb Failure relay is bad.
But still possible the brakelight switch is bad.

 

remember to check for the ground too. You can have 12v at the bulbs but if you have no return path (no ground) the bulbs will not light.

 

I've got to pick up a new multimeter. Can't seem to find mine. Anyone recommend a good auto DMM? In the mean time, I'll check the solder points of that relay. That would make sense, it seems a couple of the other relays have been failing.

 

I use a Fluke Meter at work.
I have a cheaper no name brand at home.

 

I have a fluke 177 that I love but I also have a couple of others kicking around. They all work as intended although the fluke can read frequency and a few more things. It is around $200. I have a inexpensive multimeter that I keep in the trunk and it works great too! I think it was less than $30 Even the $7 harbor freight one works fine. I like the backlight cause I cant see in the dark. If you are checking out throttle positon sensors you need either an analog (needle) meter or the fluke that has a bargraph under the digitlal readout. I also like autoranging because it is not always immediately apparent which scale I should be on (being a dumbass) , although autoranging is a bit slower. The cheapest one will do your taillights and voltage drop testing. The better meters usually read higher amps.

 

on my 91 740 i had to run new wire from the brake switch to the rear dash light to have the brake lights work(non of the three brake lights would come on) this was easier than finding the fault in the existing wire.

 

I will bet the Bulb failure relay is bad.

 

Mine kept going out after I replaced them found that it was the ground never had a problem after that the only side that I had the problem with was the Pass side.. One of those Volvo things I guess these cars will keep you on your toes ....But I will have to say good cars with 265,000 on mine I happy