[briandel]

Hi all,

Trying to figure out my no-brake-lights issue that just started. None of the brake lights work, including the third brake light; all other rear lights (tail lights, reverse, turn signals) are operable. Initially checked the fuse which was fine and the bulbs are all good. Multimeter at the switch shows no voltage on either contact...

Without a schematic, I've been reading up on other related threads and it seems that the 'filament monitor' (or corroded connectors to) can sometimes be to blame but I'm not sure where to find it. It sounds like some cars have it attached to the antenna mount but I'm not finding it there. I've also heard reports of it being behind the carpet lining on the rear drivers side somewhere around the top of the wheel well; pulled it back and couldn't locate it there either... Another thread suggested it might be behind the glove box. I'm not really looking forward to looking there unless I'm sure I'm going to find it.

Anyone know if I'm missing something simple to check for no voltage at the brake switch? If it is likely to be the filament monitor, anyone know exactly where I might find it on an 89?

Thanks in advance!

BD

 

[davide c]

Google for a Full electrical schematic for your saab model /year. Usually found on .ru sites.

 

[chengny]

Hi all,

Trying to figure out my no-brake-lights issue that just started. None of the brake lights work, including the third brake light; all other rear lights (tail lights, reverse, turn signals) are operable. Initially checked the fuse which was fine and the bulbs are all good. Multimeter at the switch shows no voltage on either contact...

Without a schematic, I've been reading up on other related threads and it seems that the 'filament monitor' (or corroded connectors to) can sometimes be to blame but I'm not sure where to find it. It sounds like some cars have it attached to the antenna mount but I'm not finding it there. I've also heard reports of it being behind the carpet lining on the rear drivers side somewhere around the top of the wheel well; pulled it back and couldn't locate it there either... Another thread suggested it might be behind the glove box. I'm not really looking forward to looking there unless I'm sure I'm going to find it.

Anyone know if I'm missing something simple to check for no voltage at the brake switch? If it is likely to be the filament monitor, anyone know exactly where I might find it on an 89?

Thanks in advance!

BD

After the fuse (24), power is supplied directly to line side of the brake light switch on a red lead. There is nothing between the fuse and the switch. This appears to be the case for all model years. See the two wiring diagrams below. One is from Haynes and the other is from Alldata.

If the fuse is good and the wiring is connected at the fuse block and switch, you should see 12 V on the red lead. Did you check the fuse for continuity with a meter? Fuse 24 is dedicated to only the brake lights circuit so there would be no indication of a bad fuse by problems with other circuits. Sometimes a fuse can appear good because the visible part of the link isn't broken. But it may have failed on either of the ends where it connects to the stabs.

 

[briandel]

First off, thanks a lot for the replies (email notifications didn't seem to work); really great info. I just got home from work and am going out now to do some more troubleshooting. While I did check continuity on the fuse itself (it's good) as well as temporarily replacing with a new one, one thing I realize I didn't check is to see if I've got 12v to the fuse... will check.

One thing I failed to mention that's interesting is that, when I first suspected the lights failed, I had a buddy stand out back to watch as I hit the brakes and one of the brake lights (top passenger side, not that it really matters) would very briefly light most (but not all) times I depressed the pedal. This made me think there might be some sort of failure in the circuit that, as soon as it has current and heats up a touch, fails. Don't know.

 

[briandel]

12v at the fuse, nothing at the switch... Suspecting a rewire as there're only two black wires, no red, going into the switch connector. Brake and clutch switch wires are wrapped in what appears to be standard electrical tape and have a non-oem-looking zip tie holding them to the plastic box that holds some of the cruise control vacuum stuff.

Guess I'm going to have to start following these wires back to the fusebox. Gah.

 

[briandel]

As I should have suspected, I might be an idiot... On closer inspection, there are two switches on the brake pedal. Pretty darn sure I've been checking the cruise control switch...

Gussing it's been the brake switch all along; will confirm shortly...

 

[briandel]

Yep, idiot. After finally finding the actual brake switch (there are two switches, the top one is the culprit, the bottom/easier one is for cruise control), I verified 12v on the red(!) wire. Pulled the switch and it's obvious this has been an issue before as it's been pulled apart before me...
It's in pretty terrible shape but after cleaning the contacts, I have brake lights. Assuming I can find one, I'll be ordering a new one tonight.

 

[briandel]

Thanks for the help @chengny and @davide c ; really appreciate it.