The Stovebolt Site Forums The Shop Area The Electrical Bay Headlight Relay Install

Happy Labor Day to all!

I believe I had ran across a post at one time where someone was explaining how to install relay's for headlights on 6 volt trucks, but I am not finding it now. My 51 was restored about 8 years ago, and got all new wiring etc but my headlights are dim, (even on bright). Dim enough that meeting another vehicle, washes out my headlights so today I checked the voltage at the terminal and with headlights on, and engine running, rpm's up, I was only getting 5.1 volts ( headlights on high beam). Not too good when the headlights are 6 volt!

I know there has been tons of threads & posts on this subject, but wondering it someone would mind sharing the link?

Thanks!

Kevin

Kevin,

A bit of searching using our very own Search the Site Tool (found in the left margin) located this 6 Volt Truck Headlight thread that includes what you need for adding "relays" for your headlights.

Just one of many posts on the topic, but I think it provides the most info.

Dan

Dan,

Thanks buddy! I appreciate that.

Before you start, check the voltage available "with headlights on, and engine running, rpm's up" at the point that you plan to provide power for your new relays. If it isn't up where it should be the relays won't help much.

Hi Bill,

I did that and got 5.1 volts at the terminal block.

Kevin,

I have an original stock 6v system with new 6v halogen headlamps. They work perfectly and are not dim or yellow. They shine as brightly and as far as modern headlights.

I think you probably have electrical problems that a relay won't fix.

What gauge wire was used in the new wiring harness?

Kevin,
I agree that installing a relay is not your answer. Check your voltage at the generator as well as the voltage regulator. 5.1 is low.
Good luck!
Jim

Hey Otto!

Gosh, if my headlights were that bright, I would be in heaven! I don't do much driving after dark, but now that our days are getting shorter, and there are still a few car cruises left this year, I know I will be driving home after sundown.

I only know some basics when it comes to wiring but I am wondering if the new wiring harness was for a 12V system, because the bulb sockets for the parklighs are dual instead of single. The wire at the terminal blocks looks pretty light gauge.

Ok guys,

I just got back in from the shop. I got my multi meter back out and did some tests. With the truck running, and higher RPM, my generator is outting out 7.5 volts, and around 6 at idle. Headlights on low beam, and higher RPM, I am getting 4.7 volts. With the truck shut off, and touching the Batt terminal on the voltage regulater, I am getting 6.39 volts.

Man, I can't spell today! I meant voltage regulator, and I was referring to the low beam terminal on the block.

Kevin

Try this:

Key off.
Attach the multimeter ground probe to a good ground and leave it there for the rest of the test.
Remove the tail light fuse on the firewall.
Turn on the low beam headlights.
Measure and record the voltage available at...
... A. the terminal board low-beam connection near the front of the driver's side inner fender
... B. the low-beam connection on the dimmer switch
... C. the common connection on the dimmer switch
... D. the headlight connection on the headlight switch
... E. the power connection on the dashboard light switch. It's on the forward end of the switch and may be marked "AMM"
... F. the non-battery side of the ammeter
... G. the battery side of the ammeter
... H. the post on the stomp starter switch that the battery cable mounts on

When you are done, turn off the headlights, put the tail light fuse back in and post the results, A through H.

Please keep in mind you don't install relay protection for voltage. A high draw of amps is what you need relay protection for. Amps are the spinach that gives Popeye (the voltage) the strength to hit Bluto hard enough to send him off to Mars. If you don't have enough volts being delivered to your headlights, you have a problem somewhere...and that generally means you won't have enough amps either. As Bill said, the dimmer switch and the headlight switch are likely suspects. I posted a repair tutorial for the headlight switch. When those get messed up you don't get enough juice going through the contacts any longer and the dimmer switch gets wet, dirty, etc and that causes it to suffer. Here is the headlight tutorial: http://tinyurl.com/2uy3ubr8

Thank you!

I will do this and report back!

Thank you Jon!

I will run through the checks. I am not sure if the dimmer switch or headlight switch were replaced when the truck was restored, or not.

I would also verify the gauge of wire used throughout the system. I used 12 gauge wire from the dimmer switch to the headlights when I replaced poorly done repairs to the system.

Certainly wouldn't hurt, but to show you how penny pinching GM was ...

The high beam wire from the dimmer switch to the left side terminal board was 12 gauge. It supplied both high beams.
The low beam wire from the dimmer switch to the left side terminal board was 14 gauge. It supplied both low beams which used a little less power.

The high beam wires from the left side terminal board to the individual headlights was 14 gauge.
The low beam wires from the left side terminal board to the individual headlights was 16 gauge. Again, low beams used a little less power.

Ok all, especially Bill Hanlon,

I finally got a chance to go out today after work and do some testing, and first I want to make a disclaimer! I have had these old trucks for the past 33 years and it seems the older I get, the more I forget when it comes to diagnosing things like this so I really appreciate the help guys!

Anyway, here's the results with truck off, and tail light fuse pulled:

A - Low beam connection at terminal board - 4 volts
B - Low beam terminal on dimmer - 4.86 volts
C - Common terminal on dimmer - 4.55 volts
D - Headlight terminal on headlight switch (assuming this is the "To Dimmer Switch"), because there is no specific headlight terminal - 5.46 volts
E - Ammeter terminal on the headlight switch (To Ammeter) - 5.66 volts
F - Non battery side of ammeter - 5,67 volts
G - Battery side of ammeter - 5.71 volts
H - Starter switch post on starter - 6.34 volts.

Hopefully, this information is adequate.

Thanks,

Kevin

I think you have the voltage readings for B and C swapped. No way the voltage goes back up. Suggestions below are with B and C switched.


A to C drops 0.55 volts. That is 10% of the voltage. Way too much. Clean up the connections on both ends and try again. If it still reads the same replace the wire.

B to C drops 0.31 volts. That is 5% of the voltage. Way too much. Clean up the connections on both ends and try again. If it still reads the same replace the dimmer switch.

B to D drops 0.62 volts. That is 3% of the voltage. Too much. Clean up the connections on both ends and try again. If it still reads the same replace the wire.

E to D drops 0.20 volts. That is 3% of the voltage. Too much. Clean up the connections on both ends and try again. If it still reads the same replace the wire.

H to G drops 0.63 volts. That is 10% of the voltage. Way too much. Clean up the connections on both ends and try again. If it still reads the same replace the wire.

So the net is that you are loosing 2.31 volts of your 6.34 available volts (36%) before it gets to the headlamps. Makes for dim lights.

All that said, a properly installed relay kit WOULD solve your crummy wiring without replacing anything except the left side terminal board to headlight wiring, which the above testing didn't even address.

Don't forget to check the ground side of the circuit as well. A loose or dirty ground will drop voltage and result in dim or intermittent light problems, even if the hot side is in good condition. Try flushing a toilet with a plugged or restricted drain system, and plenty of water in the tank!
Jerry

It'll be interesting to see if anything changes after following Bill's instructions. I'd still verify the gauge of wiring used. When the wiring was replaced by the previous owner, did he include the terminal block on the left fender?

If cleaning the terminals and connections and/or dimmer switch replacement doesn't fix the problem, I would install new 12 ga wires to headlights with the terminal block. It's pretty easy to do.

Here's a quick, simple fix that uses the square cube Bosch-type relays. I use the 60 amp ones, not because the lights need that much capacity, but the wires that come with the included mounting bracket are larger.


Here's the relay I use:

www.ebay.com/itm/283063032082?

This ad is for a 30 amp, but the same type relay in 40-60 amp fits the same plug.

Have fun!
Jerry

Jerry's drawing is great, but needs a fuse or (preferably) a self resetting circuit breaker as near as possible to the source for the battery voltage. My truck has no ammeter so I attach my headlight wire to the battery stud on the stomp starter switch. Then mine runs about 1 foot to the firewall mounted circuit breaker and then up to the relays that are mounted near the old left inner fender front lights terminal block used to be. Use 12 gauge wire for this connection.

Finding a circuit breaker specifically rated for 6v is hard to do, but there are a number of them rated for 6-28 volts. Typical 6 volt high beam current draw is around 7 amps (40 watts) plus 7 for the passenger's side so a 20 amp circuit breaker should do the job.

Sounds like you are missing some grounds someplace. Put a ground cable from the engine to the frame, from the frame to the core support & the firewall.

George

If your headlight switch is as bad as the one shown in my tutorial, you will lose voltage and amperage and the output you get will be intermittent at first and finally just lousy...and it doesn't matter how good your wiring is nor how good your ground connection is. This much junk works as resistance. What happens is the contactor bumps wear troughs in the fiberglass or garolite board, the stuff they tear up mixes with the grease used when the switch was built and it makes a non-conductive paste that stays right where it is. It is just that simple and a check with a handheld meter will show it quickly. You must get the contactor and the switch's plate as clean as brand new and if you do, you may be very pleased at the difference in your lights. Please take a look at the images below (taken from the article I wrote) and you'll see why. Good luck!

What is the stuff on the switch in the center photo?

Grease. You need that for the switch to slide properly. It is necessary to sand the plate down to clean the 5 contact points so the contactor will make proper contact again.

Hi Otto,

The truck has a new wiring harness and terminal blocks but the dimmer switch appears to be old.

Kevin

Guys,

I believe I fixed my issue. My dimmer switch was bad. I forgot that I had a new in box, BW dimmer switch so I R&R'd it. Now I have 5.98 volts at the low beam connection on the terminal block, and my lights sure look a lot brighter. Once it get's dark, I plan on a test drive to see.

I want to thank all you guys, for your help. Jon G, your information on the light switch is great and I really appreciate your tutorial. Bill H, Otto, Hotrod Lincoln (Jerry), and all the rest, THANK YOU!!

Kevin