Capacitor across brake light switch leads?

(2011-04-26 14:20:35)

1. Heavy D Says: I'm restoring an old Corvette, and installing a donor interior harness from a parts car. The harness was in perfect condition with no splices, with one exception: across the brake light switch leads, someone had spliced in a .47 microfarad capacitor. It was definitely an amateur job, and I can't figure out why you would do it or even what it would do for the circuit. I've looked at drawings for several years (the harness is a '75, although the car is older) and there is no capacitor on any drawing that I've seen.

Any ideas?

Thanks in advance.

2. Mark S Says: Perhaps he was getting a 'click' thru the stereo when he pressed or released the brake pedal (from current change when brake lights went on or off)... adding that capacitor would supress the quick change in current that could generate RFI (radio frequency interference).

And no, it wouldn't significantly 'speed' the illumination, LOL.

3. Mark S Says: Interstingly enough - there was a post yesterday with a person worried about a CLICK in her audio everytime she hit the brakes...

4. "DOZER" Says: I believe it simply stores power for when the brake pedal is pushed, and the lights are iluminated more quickly from the extra power stored by the capacitor.

Quicker brake light illumination by a few milliseconds.

5. Gary Says: Remove, it's possible he was having brake or turn signal switch problems, Just remove should be fine.

6. Rumple Says: OK, here's the deal... Old materials were better. The original brake light switch on that corvette may have lasted 10 or 15 years. The replacement switch, maybe from Mexico or China simply was not fabricated to the same standards as the original. People have been noticing this much more recently...a switch required to carry 3 amps of current is actually engineered for 2.5 amps...with a corresponding decrease in the service life of the repair part. Some reports show as little as 3 weeks of use before failure, on a brand new part. So. At some point, someone decided to install a brake light relay in the corvette that the harness came from, in an attempt to decrease current running through the switch. The capacitor was wired in to prevent point bounce and arcing in the relay, which, incidentally, was left in the donor car. You can either leave the capacitor or clip it out. It will have no effect whatsoever on the brake light circuit, good or bad.
The source box below has a link to the writeup and schematic done by David Dubois in repairing his MG...