1989 Pickup. Rear brake lights out with new bulbs. Why?

my 1989 pickup has a crapped out master cylinder. it will be fixed soon. another problem has come up and i wonder if the two are connected. after changing both brake bulbs and checking for obvious wiring breaks (none), i'm wondering if a connection between the master cylinder and the break lights exist.

Reply to
torque
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Yes. The connection is the brake pedal.

The pedal operates the master cylinder, and activates a switch.

Reply to
Jeff Strickland

so, are you saying the switch is in the master cylinder? i.e. replacing the master cylinder will solve the brake light problem. or is the switch a separate part that must be replaced, in addition to the m.c.

Reply to
torque

The brakelight switch is a mechanical switch that hits the pedal arm to turn OFF - if the pedal arm isn't returning to it's full release stop the brake lights stay on. Might just need adjusting.

If it's the Brake Warning light on the dashboard you're talking about, that is tripped by a hydraulic brake failure switch on the firewall, and usually means that one half of the brakes have totally crapped out - if that's you, STOP DRIVING THE CAR till it's fixed.

If the half that still works (usually the front) fails you have NO brakes. The back brakes can fail without a big difference in stopping distance, because the fronts do most of the work - when the fronts are out, you'll know.

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Reply to
Bruce L. Bergman

Bruce:

The brakelight switch is a mechanical switch that hits the pedal arm to turn OFF - if the pedal arm isn't returning to it's full release stop the brake lights stay on. Might just need adjusting.

there is no brake light on the dash that is on. in addition, the brake lights aren't staying on, they are permanently off. firstly, is the brakelight switch within the mastercylinder, on the floor of the cab, where? perhaps, behind the brake booster. what i need to know is, is the failed master cylinder effecting the brakelight switch because the m.c. no longer holds pressure. or in other words does pressure in the m.c. control the operation of the brakelights? my intention is to find the culprit and if i need to buy a master cylinder and a booster, the replacement cost is less if both are purchased as a pair. but, since i'm working on a limited budget, i'd prefer to only replace the m.c. if it will fix the problem. any suggestions would be appreciated. thanks.

Reply to
torque

Okay, that narrows it down some...

The only kind of brake light switch that would be on the Master Cylinder itself would be a hydraulic pressure activated style switch, and those have long gone out of style - when they fail it's usually a diaphragm crack or rupture, they tend to start leaking brake fluid, and when you run out of brake fluid you lose the brakes. And of course, this is very bad.

The last hydraulic brake light switch I messed with was on my 1962 International Scout (Girling brake system IIRC), and I think the original few decades of Volkswagen Beetles had them...

And even then, they were not "built into" the MC. They are a separate part that looked like an oil pressure switch sender, screwed into either a port on the MC, or a tee fitting on the hydraulic lines.

If the brakes operate properly and stop the car normally it probably is NOT a problem with the MC - what makes you think that it is?

Open the drivers door and stick your head up under the dash with a flashlight. The brake light switch will most likely be at the top of the brake pedal arm - look for the wires. Push the brake pedal with your hand and look for what moves and what doesn't.

They can make really odd looking switches that snap over the pedal arm pivot, but they all function the same - mechanical pressure moves the contacts, and they have to be wired to the car electrical system.

They build cars slightly different for each major market region's laws and requirements (like LHD or RHD, or a turn-signal repeater lamp on the front fender for some European countries, or a speed warning buzzer for Saudi Arabia) but apart from that there aren't /that/ many changes. Would defeat the whole purpose of Mass Production.

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Reply to
Bruce L. Bergman

I didn't say that at all.

You asked if they were connected. The connection is the brake pedal.

I do not think the two malfunctions are related, I think the switch is a failure and the MC is a failure. Having said that, you didn't tell us what the MC failure is, and why you think you need to replace it.

Reply to
Jeff Strickland

The failure of the BRAKE LAMPS and the condition of the Master Cylinder are not related. Replacing the MC will not make the brake lights work again.

If you foot goes to the floor or sinks slowly to the floor at a traffic light (or anytime you hold your foot on the pedal to keep from rolling), then you have a MC problem. As a temporary measure, you can sometimes pump the brake pedal to build hydraulic pressure, but the pressure eventually fades and you have to repeat. As the MC gets worse, your need to repeat increases.

If you lay on the floor and look up, you should be able to find the Brake Light Switch mounted to the side of the steering column support braces, it has a switch actuator that is activated by movement of the brake pedal.

Have you used a helper and a volt meter to see if you even have voltage at the brake lamps?

Reply to
Jeff Strickland

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