The car is a 2004 Oldsmobile Alero. At some point a little ways back, the cruise control stopped working. Checking the brake lights, I discovered that the brake lights were also out (all 3 - two on the side and the one on top). I checked the fuses and they looked fine, and I even swapped a spare 20A fuse to the stop lamp spot just in case. To no avail there, I replaced the brake light switch. This also did not fix the issue.
Anything else I can/should check?
You can use an automotive circuit tester to ensure that when you press the brakes, your rear bulbs are receiving current. Trace this back to originating point that has no current. More than likely, you are testing the wrong fuse.
I bet it is just a fuse issue. Check your method again. Then replace the bad fuse.
There’s a light blue wire from the brake light switch to the drivers side instrument panel fuse block. This wire junctions with three other light blue wires which supply power to the three brake lights.
Check this junction connection at fuse block to see if there’s a poor connection.
Short the brake switch connections together and see if the brake lights work.
Is current getting to the brake light switch? Do you have a test light?
You might want to consider replacing the multi-function switch if your troubleshooting comes to no avail. This vehicle has the double lever (both right and left controls) multi-function switch. It could be the cause of both the cruise control and brake light problems.
If missileman is thinking of the same switch I am, it’s located at and activated by the lever on which your brake pedal is mounted.
I don’t have access to your schematic, but I suspect the switch enables a circuit that engages a multifunctional relay the contacts of which complete the brake light circuits and disengage the cruise control. That relay, if my guess is correct, might also be bad.
Thanks for the responses guys. I haven’t been able to test anything else as I’m out of town and away from the car for a few days. But I am definitely checking the right fuse, I’ve double and triple checked to be sure. The tail lights work but no brake lights when the brakes are applied.
Would that multifunction switch be the one next to the brake light switch?
The multi function switch is under the steering wheel.
You might want to start at that brake light switch. Confirm that there is current at thr switch and then confirm that when the pedal is pressed current flows to the wire that leads to the brake lights.
Good comments above. One thing that is often mis-diagnosed but can cause this symptom is if the ground for the brake light circuit has come loose. On my Corolla the ground for the third brake light (the high, center one) is separate from the one for the other two. But maybe on this car the grounds are all shared by one contact point to the frame which has come loose or is corroded. This is especially likely if this car has ever been in a fender bender and had body work done in that area.
That’s true for the brake lights, George, but that would not affect the cruise control. When you apply the brakes, the CC also disengages, and since the CC isn’t functioning I’m looking for something in the system that responds to the brake application to effect both the brakes and the CC.
I wish I had access to the schematics. I have a feeling that with the schematic diagrams the common point would be obvious.