Mechanics

BRAKE LIGHTS ALWAYS ON -- NOT THE SWITCH!

1998 SAAB 9000

Electrical problem
1998 Saab 9000 4 cyl Front Wheel Drive

Hello.
Have a 98 Saab 9000CSE
When the car is on the brake lights wont go off. The switch operates fine. The circuit is always hot. The brake lights do go off when the ignition is off.

This indicates there must be a short from some power source that is on when the ignition is on to the brake light circuit.

Does anyone have any idea where to troubleshoot this problem? The only thing I can see in the wiring diagrams where other wires might be the culprit is the filament monitor module or perhaps the cruise control module?

Thanks!
T
Avatar
Gruvytune
July 6, 2010.




Hi gruvytune,

Thank you for the donation.

The filament monitor would not affect the lights as they are in separate circuits.

Are the 3rd brake lights turning on as well?
When ignition switch is turned on, are the parking lights working correctly?
When did the problem started, after any repairs?
AD

KHLow2008
Jul 7, 2010.
After a morning of frustration I finally got it figured out after mangling the switch to get it out only to find out its fine.

All the brake lights are lit upper mount and lowers.

Well pulling brake light fuse did not shut them off as would be figured. Pulling the parking light fuse turned them off.
So figured a short somewhere. Not what I wanted to try looking for. Well I bought the car a bit over a month ago from someone and it must have been doing this the whole time and never knew they were on constantly. Not good.
So, wanna guess what it was?

Tiny
Gruvytune
Jul 7, 2010.
Check if the ground circuits at rear of vehicle are good. When the parking lights are turned on ( they should be on when engine is running) and there are insufficient ground, the brake lights would turn on as the circuit is used for grounding.

Another thing to check would be the bulb sockets and wiring. Could they have been reversely connected?

KHLow2008
Jul 7, 2010.
Well as it turns out, not so complicated just hard to have figured it out! One of the bulbs was the wrong one. They had put a single filament bulb in the socket which then powered the brake light circuit at the same time lighting the running lights in the rear tail.

Crazy!

Tiny
Gruvytune
Jul 7, 2010.
When the history of repairs are available, such problem would be easier to diagnose when we back track. Since you just bought the vehicle, the history was not available so you woulld have to depend on luck, lol.

Glad to know you have fixed the problem.
Have a nice day.

KHLow2008
Jul 7, 2010.

AD