Brake lights staying on, cruise control not working

My guess. When the brake light switch is activated , that disconnects the cruise control. So I would assume the brake light switch is bad and stays closed all the time. WW

Brake light switch is stuck on. Not a hard fix. It's attached to the brake pedal arm up behind the dash area. Simple to R&R with a new one.

It is easy to check for continuity on the brake light switch with an ohm meter. The switch should be open when the pedal is not depressed and closed with the pedal is depressed. Before you remove the old switch, check the adjustment so that you can get the replacement switch close before you install it and then fine tune it after it is in place. Also make sure that the brake pedal is retracting fully.

If the switch is good, check for a short to ground somewhere in the circuit, starting in the trunk.

might not even be the switch but the pedal lever tab that activates it. on hondas, it's a little plastic tab that pushes through a hole. if the tab breaks apart, the switch pin pokes through the hole where the tab would be and fails to switch off the lights and switch on the cruise. costs about $2 new, or free at a junkyard [too small and they won't charge you for it].

The line to the brake lights is telling the cruise control system to shut down, as if you had pressed the brake.

I'd first check the brake light switch... is it stuck? Is it broken? Is it properly adjusted? It should be mounted on the brake pedal assembly somewhere. If that tests okay with a meter and isn't obviously bad, start checking wiring.

--scott

I'd start my search at the brake light switch mounted to the brake pedal. This switch causes the brake lights to come on, and it disables the Cruise Control.

My guess is that the switch is stuck in the position as if you were applying the brakes.

A shorted wire will blow the fuse, not turn the lights on. The Cruise should be enabled in this condition also, not disabled.

Why do you think that? It depends on the method used to activate the brake lights and crusie control. I agree that for the common brake light circuits I have seen, shorting the positive 12V feed to the lights should blow a fuse. But blowing this fuse muight also cause the cruise control not to work depending on how things are set up. Also, I can imagine a system where the brake lights are turned on by the car's computer. Such a system might use the brake light switch as a signaling device that signals the computer that the brake pedal is engaged by connecting a signal line to gorund. In such a system, if the signal line was shorted, the brake lines might turn on without blowing a fuse.

Probably you are right about a shorted wire in the trunk blowing a fuse, but I am not sure that would also enable the cruise control. And given some of the light monitoring systems used in some cars, I am not sure what a short might actually do.

Ed

This being an '89, the odds that the switch itself has shed a crunchy plastic part has got to be approaching 100 percent. Its not going to be necessary to ohm out anything or test the switch for continuity, one look at it will tell the story.

That's what caused it on my '90 Corolla. But the dealer quoted me $20.00 for the part...about a 10 gram piece of plastic...and he had to order it.

I was thnking of a very simple wiring system where the Cruise would see the brake light voltage go high because the brakes were applied, and this would shut the system down. Assuming a short, then the voltage would never go high, and that would keep the system enabled.

Having said that, if the wire that turns the brake lights on were to short, the lights would not come on and the fuse should blow. What happens to the Cruise is beyond me, I've not really given it all that much thought. Since the symptom set is that the Brake Lights are on and the Cruise is disabled, then the thing I would be looking for is a stuck brake light switch. I'd not be expecting a short anywhere in the system.

Replaced the switch, lights still staying on. Dangit.

Do the lights stay on when you *unplug* the switch?

nate

The meter will tell you what is going on. The meter is your friend.

--scott

did you check for the little plastic tab that presses the switch activator?

As it turns out, I tried taping the plunger down and the lights go off. When I look closely at the contact area on the pedal shaft, there's a hole that's *just* big enough for the plunger to fit through, so apparently something - I assume this tab you refer to snaps into that hole and broke off. Will probably jury-rig something until I can get the right piece.

yup, that's it. if you look in the footwell, you'll probably find bits of the old one so you'll have a better idea of what it looks like. new ones are relatively cheap. or they're free from a junkyard.

although they're known to fail sometimes in very old vehicles, in principle the plastic tab/plug thingie is a good idea - it offers a low friction surface which preserves the switch [there's a slight sliding motion because the pedal swings through an arc], and it provides a bump-stop for pedal rebound. one of those useless/useful things to have in the spares box.