C1 headlight Wiring Re-configuration

[Joe M.]

An associate of mine read that the voltage drop through the light switch can range from 4 to 5 volts, thus contributing to or causing the dim headlights. To bypass the headlight switch, he installed a 4 prong relay on the firewall and the following wires:
12 gauge hot wire from solenoid to relay
14 gauge wire from output side of light switch to relay
12 gauge wire from output side of relay to input side of dimmer switch
ground wire from frame to relay

If I understand this configuration, the light switch then acts to open or close current through the relay and the results is 12 volts, or close to 12 volts to the lights. Anyone tried this or does it seem plausible?

I suppose before I try it, I should see what voltage I am getting to the headlight wires; or at the output side of the dimmer switch.

[Edward J.]

Re: C! headlight Wiring Re-configuration

Joe, voltage drop of 4/5 volts is alot, I would check the voltage at the headlamps with car running, this way your truely at operating voltage, if the voltage drop is that great then there maybe some connection problems along the way to the lights, corroded wiring harness connector are common in older harnesses, check headlamp connectors first, then firewall.

The relay install is a way to devert voltage away from the headlamp switch, headlights do have a high current draw thus heating up the switch and its connectors. relays are installed in all late model cars for this reason and with the aid of computers they are turned on and off.

If all is charging system is operating at the correct voltage(13.8/14.2 volts charging voltage) and the health of the wire harness is good you lamps should light normal and there really is not a need for a relay install. It would just amount to some extra wires under the dash and the chance of having problems down the road, I am not a big fan of cutting into wire harness,theres more chances of short circuts or opens in the harness if not done properly.

[Thomas H.]

Re: C! headlight Wiring Re-configuration

If you take a volt meter and measure from the battery plus to the headlight plus when the lights are on, you can measure the actual voltage drop through the wiring.

Or measure from the headlight plus to ground and then the battery plus to ground and subtract the two numbers.

The wiring mod you describe may work in theory. I expect that the headlight switch would provide power to the relay coil, thus closing the contacts of the coil. If the contacts are connected between the solenoid and the dimmer switch input, this would switch the solenoid voltage to the dimmer and on to the headlights.

The wire going from the headlight switch to the dimmer would be the one to drive the relay coil.

I don't know if this is a wise thing to do, others may have experience with it, I don't.

I'd be more concerned about a 5 volt drop across the headlight switch and troubleshoot that first.

Tom

[Joe M.]

Re: C! headlight Wiring Re-configuration

i plan to check the operating voltage at the headlight before I mess with anything. Due to an electrical fire 5 years ago, the wiring harness is 5 years old. Several years ago, I cleaned up the headlight prongs with a brass brush and then applied dielectric grease on the prongs before I connected the headlight connector. Could not discern any difference in brightness. The only thing that makes the headlights brighter is revving up the engine. That probably means that at highway speed or less, the headlights are probably as bright as they can be.

[Edward J.]

Re: C! headlight Wiring Re-configuration

Joe, chances are if the headlights are working great at higher RPM, s then its not a connection problem, checking the charging system voltage might be the next step(13.8/14.2) voltage regulator adjustment possiably, or make sure the idle speed is correct, maybe even up the speed 75to100 rpms.

The generator speed maybe just to slow, does the car have the correct pulley sizes? Any way I don' t think that installing a relay is going to help the dimming of headlamps at idle because the charging voltage sound like the reason the headlamps are dimming. they are the one of biggest current draw in the electrical system for a C-1.

[Philip P.]

Re: C! headlight Wiring Re-configuration

I believe there is a thermal protection device (15 amp)that is built into the light switch and protects the wiring should something gets shorted. This is the only protection for the wiring so you will be bypassing this. All you are really doing is adding relay that can fail then you are without lighting.
I would find the problem of the voltage drop and fix that better off in the long run.
AS some one says my 2 cents.
Phil Porter
1960 Maroon 230 4 speed

[Ed T.]

Re: C! headlight Wiring Re-configuration

Hello Philip,

I was wondering where you got the information on the 15 amp thermal protection rating on the headlight switch? I put in a new Corvette Central headlight switch in my 62 and found my high-beams start flickering off and on after about 7 minutes. Some excitement there. My original switch does not have this problem...Ed

[Philip P.]

Re: C! headlight Wiring Re-configuration

Ed,
That information is in the 1958 Chevrolet Passenger Car Shop Manual
page 9-53 which is used in conjuction with the St-12 for some of the items for the Corvette.
LIGHTING SWITCH
The heart of the lighting system is the Lighting Switch. It controls all di and instrument lights and incorporates a 15 ampere thermal circuit breaker which protects the headlamp and parking lamp wiring. (All other lights on the vehicle are protected by fuses in the fuse block.) A current of more than 15 amperes will cause the points of the circuit breaker to open and close as they warm and cool. Thus the circuit is rapidly interrupted and restored until the short in the line is found and corrected. Protection against destruction to the wiring is thus provided and possible rapid discharge of the battery is averted. Figure 98 shows a circuit diagram of the lighting switch.
The above was extracted from the manual. Hope this helps.
Phil Porter
1960 230-4 Spd

[Ed T.]

Re: C! headlight Wiring Re-configuration

Hi Phil,

Yes that's what I was looking for. I haven't mearured the high-beam current yet, but my guess is my new CC headlight switch cannot handle the high-beam current. After 7 miniutes on HB it kicks out. I cleaned up the original 096 and its back in and working fine...Ed

[Philip P.]

Re: C! headlight Wiring Re-configuration

Ed,
That is kind of an interesting situation, your original switch could be bad and not protecting the wiring for example the circuit breaker is shorted, or the new switch is too sensitive to the current draw. I do not know what the current requirement of the high beam circuit is right of hand but I would imagine is would be somewhat less than the 15 amps that the switch is rated at.
Phil

[David B.]

Re: C! headlight Wiring Re-configuration

Hello Philip,

I put in a new Corvette Central headlight switch in my 62 and found my high-beams start flickering off and on after about 7 minutes. Some excitement there. My original switch does not have this problem...Ed

Ed,

I had the same problem with a replacement switch for my '57. There is a bi-metallic contactor in the switch that is meant to heat up and interrupt the circuit if the current flow is too high. I bench tested it and found that the contactor was too sensitive and tweaked it very slightly. The problem is gone now. Over tweaking would be bad of course : )

Dave

[Ed T.]

Re: C! headlight Wiring Re-configuration

Hi Dave,

Thanks for the info. I'll hook up an amp meter next weekend and see what the headlight HB draws.

Does anyone know how much current quad headlights ('62) on LB and HB should draw?...Ed

[Philip P.]

Re: C! headlight Wiring Re-configuration

Ed, it depends on the type of lamps you have some of the replacement are 60 watt and 40 watt high and low beam that would make it draw about 15 amps at 13 volts ..ohms law P=IE 200 watts = 15amps at 13volts, this is not exact but a rough estimate..that makes the switch border line at best. The newer lamps may be the problem as they are brighter and may draw more current. I have a new set of correct T-3 and although I have not been out at night with the car I did drive across the state (Washington) with the lights on and did not notice any problem, they were always on when it stopped anyway. I do not know what the wattage of older lamps were off hand.
Phil

[Scott K.]

Re: C! headlight Wiring Re-configuration

Hello Philip,

I was wondering where you got the information on the 15 amp thermal protection rating on the headlight switch? I put in a new Corvette Central headlight switch in my 62 and found my high-beams start flickering off and on after about 7 minutes. Some excitement there. My original switch does not have this problem...Ed

Ed -

What type of lamps do you have? We're going to look into this.

[Jack H.]

Re: C! headlight Wiring Re-configuration

"The only thing that makes the headlights brighter is revving up the engine."

That's the nature of the beast!!!

Generators have what's termed a 'cut through' curve (search the archives). Basically, their output is a function of RPM. At/near curb idle, they supply little/no charging current and you're stuck with the battery to run things.

Delco 'tweaked' the generator to achieve different cut through profiles for specific vehicles that spent an inordinate amount of time either at idle or at low speeds (e.g. police cars and taxi cabs). But, Corvette was NOT such a vehicle and was equipped with a rather standard generator...

You don't see appreciable charging output until you get the RPMs up to +1500. Expect the B+ supply rail to rise from whatever the battery's native loaded voltage level is (probably 10-12 volts) to a normal battery charging level (13.8-14.4 volts) as the engine speed increases from idle.

That's just the way these classic cars actually worked, mon!