Brake (Stop) lamp capacitor question

[c4koh]

All,

RE: my 1992.

A friendly neighbor on the road told me that my stop lamps weren't working. Upon review, the CHMSL was working, just the 4 tail lights. Park and turn were fine.

OK, looked in the FSM, found the switch and it's operational.

As described, there's a 33uF capacitor on the Orange/Blue (for the CHMSL) and same again for the White/Blue (for the 4 turn lights).

Long story short - and my question: I removed the capacitor on the white/blue combo (pins A+B in the connector), but replacing it... they still didn't work.

After trying out various tests, I got to the position where the capacitor was removed - and hey presto!! The 4 tail lamps work fine (high power on brake). Full service resumed - but no capacitor... not as the FSM describes it should be.

So - should I look into it more? What does that capacitor (across the brake-pedal switch unit) is supposed to be doing??

Any 2c appreciated.

Steve

[Franke]

C4koh, usually when a cap is placed across any switch contacts its primary function is to prevent arcing to prolong contact life. I would look into it more.

[WVZR-1]

Originally Posted by c4koh

So - should I look into it more? What does that capacitor (across the brake-pedal switch unit) is supposed to be doing??

Any 2c appreciated.

Steve

Maybe only a WAG but I believe it maintains the circuit for the ABS, EBCM and ASR functions. In real early cars Corvettes included there was a capacitor placed there for radio interference and you could induce a click into the audio/radio systems by pumping the brake pedal. A click - click! It is NOT I'm sure for that. C3's used them.

The wiring diagrams for early C4's with no ABS don't show that capacitor, I used an '84 wiring schematic to compare. I know that in later OBDII cars there are codes that rely on those circuits to be active but I don't recall ever seeing it in the FSM for the C4's. In your '92 FSM check, ABS, ASR sections. Maybe there is a reference to them there.

I just read this and I recall hearing it maybe before that if the stoplight circuit is energized in this fashion it relieves the stress on the switch and maybe also increases response to the stop lamps by milliseconds.

"Franke" it seems posted while I was tapping the keyboard similar thoughts!

[WVZR-1]

The first year those capacitors make an appearance on a C4 schematic is '89 so that rules out "maybe" the ABS thoughts. In anticipation of the CCM were they added to the '89 product?

[c4koh]

Well,

There was a problem with the capacitor in there (loose or popped) and I ran down to radio shack who did not have a .33uF on hand. So, I'd like to say I remember my high-school electronics, but I didn't ;-) so I googled and 2 caps in parallel can be added. So I got a .22uF and .1uF = .33uF and tried that... no effect!

Only when I removed the cap did they start working - so not sure if I messed up with the wrong type of capacitor, or not. I'll get a proper .33uF ceramic over the next week, and try again. In summary, it's beautiful Sunday weather here in NY state and driving was more important than arcing across a terminal temporarily!

Drive out was beautiful - saw an early silver/blue C2, met some owners in a bagel / muffin deli with 2 C6s (nice vehicles) and a beauty of a '72 Red Stingray. So drive out was worth it - but will leave the mid-week duties to review the capacitor later!

Steve