[flyby]

I am a fairly new owner of a 1997 Saab 9000 Aero, which has been giving me trouble with the brake, tail, and dash lights.

When I bought the car, the owner said that the "brake light out" indicator on the dash would not turn off, but that all of the rear lights were functional. A couple weeks later, the right brake light failed and I went to Kragen to pick up some replacements. I was in a hurry so I had them bring up the bulbs on the computer and grab them for me...didn't put them in the same day.

One night I turned on the car and noticed that the dash gauges and climate control console failed to back light. I don't drive at night often, but always drive with the headlights on, so they may have been broken for quite some time. That same evening, I got pulled over and given a fix-it ticket for my brake light that I had yet to fix.

A couple days later, I put in a new rheostat having read that it could be the point of failure for the dash lights...still no lights. I then replaced the brake bulb and it seemed to work fine. However, that evening I kept messing with the rheostat while I was driving and noticed that the dash lights came back on! A miracle...or so I thought.

I pulled into a gas station to clean my windshield and the car wouldn't turn off! I could pull the key right out of the ignition and it would still be running. In the process of getting the car back home, I also noticed that my dash lights would now ONLY light up when I hit the brake pedal.

Some forum detective work let me know that I had the wrong bulb in the brake light socket...single filament rather than the double filament it is wired for. I put the OLD, apparently dead bulb that got me a ticket back it and it seemed to light up just fine, and the car turned off each time I drove it that day.

But NOW, the taillights do not light up when the headlights are turned on, and the dash lights are back to being completely dark. Turn signals, flashers and brake lights all work. But this thing is completely unsafe to drive at night!

I noted that the instrument cluster, rheostat, and brake lights are all on a single fuse. While the taillights are on another. Because the double filament bulb serves as a taillight AND a brake light (when it gets brighter) I think that my single filament bulb jumped the contacts and burned out a relay or switch associated with the taillights.

All of my fuses check out, rheostat worked for the short time that the dash lights were lit up, all the bulbs are good, and the circuit board looks clean.

What do I look at next?! Is there a taillight relay that I can inspect? Could it be something fried at the dash switch for the lights?

 

[chengny]

Whoa! That's a tough one.

There are issues with so many seemingly unassociated components. Maybe someone has seen this particular behavior before and can offer some specific advice. I can't.

Unfortunately, and you're not going to like this, there is probably a ground fault somewhere. I couldn't even venture a guess without looking at schematics for a long time.

But first - when something like this happens, the best thing to do is ask yourself "What was the last thing I did before this problem appeared?".

In your case it seems that it was the installation of new lamps in the rear lighting clusters. It is hard to tell from this statement:

When I bought the car, the owner said that the "brake light out" indicator on the dash would not turn off, but that all of the rear lights were functional. A couple weeks later, the right brake light failed and I went to Kragen to pick up some replacements. I was in a hurry so I had them bring up the bulbs on the computer and grab them for me...didn't put them in the same day.

You mention that you didn't install them that day. What you fail to make clear is whether, at some point, you did eventually install them.

Did you ever install the new bulbs? And if so, was it only at that point that these issues developed?

Re-check your work. I would pull every bulb in both rear clusters and the high-level brake light assembly. Check all bulbs for proper model number and also inspect each bulb socket for excessive oxidation. Repair as necessary.

There is one component that comes to mind which is cross-connected to several lighting circuits (and is directly involved in brake lighting and dash indication). It is the rear light bulb filament monitor. It is located in the LH side of the trunk. Fold down the vertical carpet and look under the bracket for the power antenna. The rear filament monitor is a long white box clipped to the antenna bracket (I think).

The only way to eliminate/confirm this as the root cause is to change out with a known good unit.

As far as the engine failing to shut down when the key is off/removed...?

That is usually an ignition switch issue. I can't think of any common circuit to the rear lighting that would cause it, other than the critical ground that was initially mentioned. Maybe it was a co-incidence?

 

[dmgb5]

There's a lot going on there. Car not turning off would most likely be your ignition switch. A dodgy ignition switch can cause all sorts of weird side issues which might be related to your interior lighting problems.

When the ignition switch failed on my sister's CSE her headlamps wouldn't turn off. (switch off, car off, and key out of the ignition)

Sorry, not much help with the brake lamp issue.