Look Ma! No Brake [lights]

[SaxMan]

So, I was rather chagrined to discover that the brake lights are now inoperative of Baby Blue. Turn signals and running lights, though, are working fine. My guess is it is the brake pedal switch. Continuity and voltage testing seems to indicate that is the situation, but I'm having a hard time getting consistent results, which may be user error. My thought was to pull and inspect the brake switch and put current through it from an outside source and see if it is the problem. I sure hope I don't have to go wire tracing. :grief:

EDIT: Answered my own question. Once I pulled the brake switch and hit it with an external power source, it was clear that was the problem. It wasn't completely shorted, but only a fraction of the incoming voltage was making to the other side, hence the inconsistent results from the continuity and voltage testers while hooked up to the car.

 

[dklawson]

I don't follow the test method you described.

You wouldn't apply a voltage directly across the switch, you would use the switch in a circuit with a power supply and a load (like a light bulb). When the switch is in its normal state (open) you should find the voltage across the switch to match whatever the power supply is. When you actuate the switch the voltage drop across the switch should be very low, approaching zero.

Alternatively, if you just put a multimeter across the switch terminals (no wires attached) then you should find infinite resistance when the switch is open and very low resistance (approaching zero) when the switch is closed.

 

[JPSmit]

or you could just bypass the switch - if the lights go on - it is the switch. :eagerness:

glad you solved it

 

[Pythias]

Those switches are cheap and available from NAPA. Change it fast enough, and you don't even have to bleed the system.

 

[SaxMan]

or you could just bypass the switch - if the lights go on - it is the switch. :eagerness:

glad you solved it

Good advice! I should have thought of that last night. I tried that this morning. Put the two wires together - brake lights go on. Separate the two wires, brake lights go back off. Yup. It's the switch. When rewiring, does it matter which wire goes to which terminal? I don't think it would, but electricity isn't exactly a strong suit of mine.

 

[Jim_Gruber]

For this application it will not matter. All the switch is doing is twisting your wires together. Count how many threads are exposed. Don't turn the switch in too many turns or it can interfere with brake pedal operation.

 

[nomad]

I believe that the current crop of new switches is still c**p so I would not throw away your old switch. You may be able to disassemble it and rebuild it. Also wanted to mention that every car has a brake light switch and you may be able to find one that can be jury rigged to work better. I mounted one to work off the pedal on my MGA with just a bit of steel strap to hold it. Seems like someone has come up with a switch off another car that can be used.

Kurt.

 

[dklawson]

Bill and Jim mentioned two different switches, hydraulic and pedal. I did not think to ask SaxMan which switch he was dealing with.

Like Kurt said, there are a lot of stories of the hydraulic brake switches failing on many British cars, particularly if DOT-5 brake fluid is used. There are also many reports of cheap pedal actuated switches failing.

I replaced the hydraulic switch on my Mini with a pedal actuated switch. I did not use a Lucas style switch but used an industrial MicroSwitch I had in my collection of parts. On the Spitfire, when it's pedal actuated switch failed I followed the advice on part of this board and bought (from Rock Auto) a BMW 2002 pedal switch instead as it is a "more" sealed unit that has a metal shell and comes with the mounting jam nuts.

 

[SaxMan]

This is a pedal actuated switch.

When I put power across it, I was using a 6V/12V battery charger using 6-volts DC, one of the alligator clips on the switch, the other clip was grounded. The switch was in the closed (power passing through) position, and while I was sending 6 volts in, I was not getting 6 volts out. It wasn't zero, but it was a fraction of what was going in.

I don't know if this was proper methodology, but the brake switch bypass test, putting the two wires together, certainly laid to rest any doubts that it was the switch. It is likely the original switch, as I'm finding several of the original switches are becoming intermittent or failing outright. It's hard to fault Lucas "Prince of Darkness" electrics when these switches have lasted 46 years without replacement.

 

[dklawson]

Thanks for the further explanation.

If you are looking for a heavier duty replacement, consider the BMW pedal switch I mentioned earlier. Rock Auto shows the Airtex brand switch available for a little over $10. (AIRTEX / WELLS 1S5570)

 

[SaxMan]

New brake switch installed. Life is good again.

 

[nomad]

New brake switch installed. Life is good again.

So, did you go with Doug's Airtex switch??

Kurt.

 

[SaxMan]

So, did you go with Doug's Airtex switch??

Kurt.

I went with the VB replacement switch. The switch also came with the wiring and wiring sheath all the way to the connectors, so it was a fairly simple swap. I did it right after I put my daughter on the bus so that I could use the car on a beautiful day today -- 75 degrees, sunny and dry.

 

[nomad]

I went with the VB replacement switch. The switch also came with the wiring and wiring sheath all the way to the connectors, so it was a fairly simple swap. I did it right after I put my daughter on the bus so that I could use the car on a beautiful day today -- 75 degrees, sunny and dry.

Hope it stands up for you.

Kurt.