marshal135

Hello,
As some of you may know, I finally sorted out my head light vac issues last year.
Allot of help from the forum thank you,again.

I purchased a NOS switch off ebay in the rectangular carton which was already open. It is possible it was a warranty part that made it back into circulation years later, just speculative?

My problem is the interior lights go out after a short drive and return if I drive a distance.
With the old switch the dimmer was shot the lights remained on full bright only no dimming capability.
The switch works great on the vac side and I can come out several hours later and start the car and the lights remain down.
I have the interior dome lights when turned all the way to the left.
When working I can dim them just fine. Its frustrating to have had the dash out and thought this problem was behind me only to find a new old stock switch acting up.
If the rheostat was burned out like my orig. one then it wouldn't return on at its leisure. It didn't do this initially when I installed it.
I thought maybe it was doing this when it got warm but to come back on an hour later is kinda got me baffled.
It almost has me believing its a loose ground?
The head lamp connector is orig. and one piece.
Where should I begin checking?
TIA
Marshal

SwampeastMike

When the dash lights are OUT, test both sides of the Instrument Lamps fuse. If you have positive voltage (it will vary depending on the dimmer setting) the headlamp switch is OK. If you don't the problem is either the switch or the wiring to the fuse.

In the event you have power at the fuse the problem may be either the ground or the power. Older Corvette schematics aren't as good as modern ones--especially with regards to harness splicing and complete ground paths--but a review of the individual circuit schematics for your year may well indicate if a bad power or ground connections is the more likely.

SwampeastMike

BTW, the above test works because the instrument panel lights actually get their power from the Tail Lamp circuit in the headlight switch. The power after the rheostat then passes through the instrument panel lights fuse. In theory this arrangement prevents a short in the instrument panel lighting from either burning out the rheostat or taking out the tail light fuse. In practice the unusual rating of the IP lamp fuse (6A in my '79) is often replaced with a higher amp fuse should it blow. If the short isn't corrected the rheostat will fry with a higher amperage fuse installed.

0Willcox Corvette

I think that the next time I get some free time, I'm going to draw up a clear version of the headlamp, courtesy/dash lamp schematic. Possibly this picture will help you understand the circuit too.

Peterbuilt

Check your ground here.

TimAT

The above picture/diagram- the one marked as on the left front door jamb- it is there, but it's ABOVE the hood release handle bracket.

SwampeastMike

When you do find the time don't forget to stress the importance of a properly rated IP Lamps fuse! Use a higher amperage fuse and the rheostat becomes the de-facto fuse!

0Willcox Corvette

Good point... and the de-facto fuse also becomes a fire hazard.

I've got a list of projects here.. some small... some that I'm working on that are large (videos)... but the schematic shouldn't be that much of an issue this winter. Video's.. man they are time eaters for me.

Ernie

marshal135

Thank you everyone.
I've got some home work and will report back with my findings.
Marshal

marshal135

Thanks Ernie
That is a great break down.
Marshal

0Willcox Corvette

I'll be gone tomorrow and won't be back until Monday, but if you need to message me send it to Service@Willcoxcorvette.com.. It pings to my phone, my laptop and my home computer..... or hit Mike or Pete up on a PM.... (Both are damn good with electronics)...

E

BLUE1972

To me it sounds like the wiper blade on the rheostat in the headlight switch is loosing contact with the winding when the switch heats up.

I have observed this problem with a few of the imported switches.

These switches (sometimes) will start to flash the headlights when the high beams are left on for 15 minutes.

Just my best guess..

marshal135

Ok here's what I did yesterday on my day off.
Hello,
I'm still in need of additional help. Here's what I did so far.

I pulled my instrument panel fuse. I checked it for continuity it checked out. It is the right amperage at 1AGA 5 amp. I checked this in my original copy GM shop manual. It calls for a 5 amp.

I got my trusty Greenhill volt meter out and checked the terminals at the fuse block.
With a test lead on each contact I received zero volts with head lamp switched in the off position and .05 when pulled on to the 1st and second positions of the head lamp switch. This mimicked as if the fuse was installed.

It appears, I'm receiving current to the fuse block then passing through both sides of the fuse block fuse terminals and can be interrupted by the switch.

So my dilemma appears to be after the head lamp switch and in that circuit that leads to the bulbs in the dash.
That must be the break in the link.
I will also check to make sure the ground wire is securely attached to the metal portion of the kick panel above the hood release handle.

Any and all leads welcomed.
Thanks,
Marshal

Bergerboy

I'm having similar issues.
I'm popping the tail light fuse whenever the tail lights are on, AND the instrument light rheostat is dialed all the way up - pops every time - I can watch it happen as I turn the dial. Although, I get NO instrument lights at all, either before of after the fuse blows - CURIOUS!


Checking all the connections and grounds behind the dash now, and not finding anything obvious. There's nothing jumping out at me.
So I went and ordered a new switch (worth the $35) to see if that's the culprit.
Any clues/hints would be appreciated.

marshal135

Bergerboy,
I'll share as I learn
Marshal

BLUE1972

I would vote for a bad socket on an instrument bulb or a bad bulb where the element has fallen into the base and shorted it out. Sometimes the dimmer is reducing the current and the fuse will not blow. Also I would look for a grounded + wire.

If I remember right the headlight switch will also turn on the rear light in the storage area - another bulb / socket to check.


I just did a friends 69 and the left rear tail light socket shorted out. The solder bump on the bulb deformed and shorted.

marshal135

Still trouble shooting.........
Marshal