VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 1938 Chevy Headlight Relay

I keep seeing 6V fused headlight relays for the 38 Chevy for sale on E-bay yet I've never seen a wiring diagram showing it. Was this an aftermarket item? thx Billu38

I don't believe they came from the factory with one. Mine doesn't have one. If one's going to halogen lights it probably wouldn't hurt to put one in.

http://www.chevsofthe40s.com/detail/10727/Chevrolet_Headlight_Relay_6_Volt.html

The 6 volt headlights ( Halogen type) will not work without a relay. The experts say mount them as close as you can to the headlight for better lighting. I like mine.



I have two mounted near the hood latch (bottom left of engine bay),you can see a yellow wire attachment in the photo.



You can see the purple wire in the corn of the photo going to one of the relays

Thanks for the input Gents. Billu38

Steve, just so I'm sure of what you posted..you are agreeing that the original schematics DO NOT show a fused relay..RIGHT? I understand your comment about the Halogen lites... Billu38

I think you will find that your headlight switch has a built in circuit breaker like the later ones, but I would install a relay like Steve has.

Yes. The only relay is a horn relay for the twin horns,they mount on the horn bracket. The single horn doesn't have one.

The lights on a 1938 are fused. The 1948 was the first year to use a circuit breaker.
A head light relay was introduced about the time sealed beam in the early 1940's. It was fused and it use was to by-pass old wiring and switches in older models and bring the eletrical feed up closer to the head lights for a brighter light It was also used when a high current draw type of head light was used to prevent buring out or damaging the head light switch. It was never used in production.

There's only one fuse for the entire car,it's on the amp gauge.

No circuit breaker on the headligt switch. Only one fuse or breaker for the entire car. I'm surprised that most of the 38s don't catch on fire. I rewired mine because everything was showing bare wiring. I had a few smoking and sparking events before I did that. If I were going to rewire with the orginal type wiring ,I would put a off/on switch at the battery.

The harnesses from YNZ only look like the original. The wires they use (at least on mine) are modern PVC coated wires that are then covered with cloth to look original then clear coated for protection of the cloth.

The wiring on mine could have had asbestos coverings.

The fuse on the ammeter was for the lights only. The ignition supply and the gas gauge were not fused. If you installed a heater or a radio then they had their own fuse.

I don't see how does having the relay close to the headlights provides better lighting? It is merely a switch that provides a direct path from the headlights to the battery. Where the relay exists in that path is immaterial as when the relay is energized and internal switch is closed it is if the relay is not there and you have a wire between the battery and lights.

Mike

The power to the headlights doesn't have to go as far using a relay.

Mike it is apparent that you don't have a lot of electrical knowledge. Headlights require a lot of power. (Wattage) (volts times amps equals watts ) and with a six volt system that requires a lot of amps. Resistance limits the amount of amps, therefore the shorter the wire from the battery to the headlights the brighter the lights. A relay should connect the battery to the lights to keep from having a lot of current pass through the light switch. The relay works the same way that the starter solenoid works.

Halogen light bulbs will not work without a relay. Huge difference in the amount of light that Halogen bulbs put out. Strongly suggest using them if you are really going to drive the car. If you do use Halogen "DO NOT TOUCH THE BULB WITH YOUR FINGERS" when installing them. They need to be free of any type of oil on the surface.Use alcohol to wipe off the bulb surface "BEFORE" you install them.

You can mount the relay under the dash if you like but the lights won't be as bright.The shorter the wiring from the relay to the lights the better.I agree the relay would LOOK better under the dash,out of sight.6 volt wiring is much different than 12 Volt wiring.The size of the wiring for 6 Volts needs to be much larger if the load is large. I have a #0000 cable going from the starter to the battery,it's huge, but it does make the starter turn the engine over much better.

I guess we're in the wrong forum again. This should be in the Electrical section..grin

Guys, the relay is a switch.. your making it sound like the shorter the wire from the relay to the lights the more power on the lights. You also have to run a dedicated sizeable wire from the relay to the battery. When you engage the relay by applying power from the headlight switch, the relay makes a direct contact between the battery and the lights and the length of that wire's resistance affects voltage drop and current to the lights (shorter the better). My point is there is no difference in the relay being next to the battery or next to the headlights, once the switch is engaged it is effectively a straight wire.

Mike

Mike

The circuit for the hedlights will be better if the relay is in a direct line from the battery to the headlight. The wire from the headlight switch can be a smaller wire than the one from the battry to the relay and to the headlight. Your mounting the relay under the dash isn't efficient, do you wnnt the wireing to look good or the headlights to be bright?

The longer the wire the more you lose,the shorter the wire the brighter the lights.If you run a 2 ft long wire VS a 15 ft wire and use a meter ,you'll see a drop in the 15 ft pc. The relay keeps the load off the switch also. 6 volts isn't many volts.

Getting back to the starter/battery cable, the loss of current is a big drop in just a few inches, if it's 6 volts.

Exactly.

Ok Guy's; I have two of these relays on my 37 MD. One under each headlight wiring junction, but they have no wires on them. They were on the car when I got it, but never wired up. Do any of you have a wiring diagram on this? Thank You for any help on this. Also, what size wire would I use? Thanks agin.
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Joe's 37

This diagram shows a modern standard relay pinout for a low beam and high beam relays.


My orig. Delco relay has 3 terminals and the case is grounded.
H = headlight
B = battery
S? = I think it's S but it goes to your headlight junction terminal from dimmer switch.

For wire, it depends on what bulbs your going to run..

ex: 35 watt/6v = 6 AMPS x 2 = 12 AMPS (14 Guage)

wire ratings are
Guage.....rating
10........35 amps
12........28 amps
14........18 amps
16........10 amps

Mike