Guys,

We're in the process of doing some headlight upgrades (the popular Daniel Stern upgrades) and noticed something weird with the car. This particular problem behavior has been something that has happened to my car for as many years as I can remember, and I just want to ensure that this wasn't designed this way.

Here's the test:

1) Open hood
2) Turn on foglights by flipping foglight switch to on and pulling back 1 notch on headlight switch

Fogs should be on now. Look at your headlights in the closed bucket position. Are they dimly lit?

Mine are dimly lit until you turn off the foglamp switch which cuts the power to the foglights and the dimly lit headlights.

So basically what's happening is that there are about 7V of power going to the headlights when they are not on (only fogs on), and with the new wiring harness that we're using for the DS light upgrade, this is causing the relay to trip and turn on the headllights. Nothing like 95w bulbs shining right in your face. :-)

We've replaced the headlamp switch, and the fog light switch tests perfectly fine. Only thing left to check is the dimmer switch.

Anybody seen this type of thing before?

Rony

 

It may not apply being a different year but I just confirmed my 93 does not work like yours. Sounds more like a bad ground to me than a problem with a switch, check the fog lamp and headlamp circuits using the FSM and verify the ground terminals are clean and tight.

 

My 89 doesn't do this either. At position 1 - only the parks are on, gos also if the fog switch is on. NO headlight glow of any kind. I agree it seems like a bad ground. Maybe a previous owner tried to re-wire so fogs could be on in any switch position. I did that in a jeep, but used more relays to do it.

 

Grounds verified good. With the dimmer switch disconnected, we still seem to be getting power to the high beam relay.

PS: No previous owner. I'm the only one. :-)

Ron

 

This may not apply because I'm going by my 93 FSM but the wiring diagram I have shows connectors (C187 and C188) and also splices S109 and S110 in circuit 150 between the fog lamps and the ground terminals. If you just inspected the ground lugs at the frame rail you could still have a problem at those points. My diagram also shows a ground for the headlight switch located under the dash at the left side kick panel.

 

I just encountered this same problem when doing the DS upgrade. There are three wires going to the headlight, black, red, and green. You need to ground the green wire going to the headlight (either passenger or driver side is fine) to the chassis. I used the ground at the front of the engine compartment right below the headlights (there's one on each side of the car). I used the one on the passenger side since that one was not needed for the new relays in the upgrade and was easiest to get to.

 

OK. This upgrade has certainly created enough "we didn't expects" that these lights better be good. :-)

The green wire appeared to be the culprit to fixing my dimly glowing headlights when the foglamp switch was on. When we regrounded that to the chassis ground right under the headlights, it fixed the problems with the dim headlights when foglamp switch was on, but now the car has no bright lights. Putting that green wire back to its stock location and grounding point makes the brights work again, but now when the fogs are on and the headlights are in their IN position, they are dimly lit.

Some notes from my mechanic:

Are the '87 to '89 headlamp circuits the same in operation?
Things I see in the '87 headlamp relays for the door operation, looks like the headlight control unit replaced that, but that doesn't really come into play with the lights itself.
Drill down to the '88 & '89 lighting circuits being the same (which I think they are)

Second, could anyone verify that your foglamps go off when you switch to high beam?

Both the '87 and '88 shop manuals I'm reading do not specifically state that little tidbit........and now I'm a little hesitant to compare my '94 to an '89, since they made some minor changes along the years....
I did find the correct wiring color codes in a Haynes Manual for 1988 Corvettes. It doesn't match the factory shop manual, so maybe finding a '89 is key...

Could anyone possibly scan a few pages from the 89 Helms manual for the fogs and headlight circuits? We're missing something really simple here. :-)

Thanks,

Ron

 

If your headlights no longer dim when you grounded the high beam green wire (when you turn on the fog lights), then the fog lights are grounded to the high beam filament. If I remember correctly '89 is the first year they did that. To sort out the other problems, how are your relays for the upgrade wired?

On mine I have the driver side green high beam wire going to the high beam relay terminal 86 and same side red low beam wire going to the low beam relay terminal 86. I have the driver side black ground headlight wire (the one next to the red and green wires) going to the low beam relay terminal 85. The passenger side black ground headlight wire goes to the high beam relay terminal 85. The passenger side green high beam filament is grounded to chassis, the passenger side red low beam wire is not connected to anything.

Also if you look at the relays you will see two terminals labeled 87 on each relay. For the power to headlight wire that these use make sure that on one relay you use the upper 87 and the other relay the lower 87 or vice versa. The main power wires from terminal 30 are connected to the alternator and the grounds from the headlights themselves go straight to the battery negative.


Does your setup vary from this in any way?