Ci electrical mystery...

[Dave Suesz]

I have seen a "radio suppression" capacitor offered, which is supposed to connect to thte headlight switch and ground somewhere under the dash. It is shown in the 56-7 Assembly Manual. Naturslly, I have a 55. There is a spade connector, unused, at this location on the switch. The grounding point shown in the 56-7 Manual does not appear to be present, or at least used for anything. Should I have this cap? What will it improve? WHat is it's value, in $ as well as mf? Are there any other caps missing from under the dash, like on the voltmeter?




55 Engine

[Jack H.]

Re: Ci electrical mystery...

Later straight axle cars moved the headlight RFI cap onto the back of the instrument cluster connecting at the ammeter (ammeter see's all electrical distrubances in the system). Since Corvette was a fiberglass body unlike pass cars & trucks, the long wiring runs from the switch to the headlight were prone to acting as antennae and broadcasting transient distrubances associated with turning the headlights ON/OFF as well as using the dimmer switch. These headlight capacitors acted as a short circuit to ground for the AC switching transients associated with headlight current flow changes.

You just 'might' be able to distinguish a difference with the capacitor uninstalled IF you're driving the car in an AM fringe reception area at night and using your headlights--you might hear 'click' noises without the cap present as you turn headlights ON/OFF or execute dim/bright changes.

What's the D-value of this cap, beats me.... The typical value used for this application on later era Corvette was 0.5 uF with a 200 VDC rating to get it into the ballpark for a proper low pass filter to the headlight system.

On other capacitors used, you should find them called out in the radio option section of the AIM as they were not installed unless the car was ordered with a radio for cost saving purposes....