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Adding headlight relay using factory wiring? 1936 Special


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I have seen a few threads about people adding a headlight relay and I wonder at which point in the wiring you did this?

I have a new harness coming that follows the original patterns but upgrades the light circuits to 12 gauge. The larger wire should reduce some voltage drop but I also like the idea of using a relay to further reduce drop and reduce wear on the headlight switch.

My initial thought was to put relays out at the terminal blocks near the fenders but they would be hard to hide and look out of place. That is ultimately why I up-gauged the light circuits.

The next thought was that I could use the standard harness and instead of connecting the light circuits to the light switch I'd connect them to relays under the dash and run control wires to the headlight switch to trigger the relays. This was looking really promising until I finally realized that the dimmer switch really only dims the passenger side headlight. On my switch, the #5 terminal is connected directly to the high beam on the driver side so when I pull the switch to country mode the driver side is always on high and only the passenger side has dimming. Very odd; I'd have thought they would be on the same circuit or at least that it would the be light that blinds the oncoming driver that would have been dimmed.

I would like to retain the capability of having high beams but since I don't want to always have the driver beam in high mode it seems I'd either have to retain both city and country modes on the headlight switch or run and/or splice additional wires. Since I have a brand new harness I'm not keen on modifying it so I'm going to have to stick with maintaining both city and country modes on the switch.

I think I can accomplish this by using either 2 or 3 relays. It seems kind of complicated so if people can point out any flaws or offer other suggestions I'm all ears. Here is what I think would work:

  • In city mode the light switch energizes terminations 1&4 which route directly to the low beams so I can easily connect the wires from the harness that would have gone to 1&4 on the switch to the powered side of a relay and connect control wires for this relay to terminations 1&4 on the headlight switch.

  • In country mode the light switch energizes terminations 5&9. 5 goes straight to the driver side high beam and 9 goes to the dimmer switch. The power from 9 goes through the dimmer switch to light either the low or the high beam on the passenger side light depending on the position of the switch. In the 2 relay option I'd connect the wires from the harness that would have gone to 5&9 to the powered side of a relay and run a control wire to either or both 5&9 on the headlight switch. In the 3 relay option I'd have a separate relay for both 5&9.

Any comments or suggestions on this plan or comments as to how others tackled this would be very welcome.

Jeff

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I think I would try to integrate a relay box into the terminal blocks. Get or make a small box with air circulation holes that will mount to the existing terminal block holes in the fender. Then mount the block on the box. Sneakily lead your wires in and out of the new relay box and it should look pretty clean.

There is a pretty nice 1930's Rolls-Royce out there with an auxiliary fuse panel under the dash that I made with some period Bakelite as a cover. Just blend with the original design and materials. Sometimes a rounded corner is all you need to give that manufactured look.

Bernie

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In my early reading I found time and again that you want to put the relay as near as possible to the thing that will consume it. That is what led me to originally wanting to put them on the terminal blocks. The challenge in hiding them up there wasn't too appealing but after I realized how funky the factory wiring is I realized it would require me to either modify the stock harness configuration or put 2 relays on each side of the car (total of 4) as well as run a 10 gauge power line to each of the sides of the car. Hmm... I just had a flash of a thought. Those headlights are awful big and I wonder if I could place the relays inside them?

Grant, did you mean that to be effective I'd need separate relays for both low and high on both sides of the car for a total of 4 relays? Perhaps I missed something but I haven't run across anything to suggest that before. Then again, I started this thread because I was looking for more details on how others did this because that kind of detail wasn't in my previous reading.

The other big benefit I read about using relays is to remove the wear and tear on the headlight switch as well as remove the voltage drop through the headlight switch. I like this concept and I believe that whether I put the relays at the terminal blocks or under the dash that I should realize this benefit.

I appreciate and understand the comments about putting the relays close to the headlights but after looking at things more I'm leaning toward a compromise of using 2 relays hidden under the dash. At the very least, this would give me the benefits of reducing wear and tear on the headlight switch as well as remove the voltage drop through the headlight switch. The new harness does have a heavier gauge in the light wires so hopefully that offsets any inefficiencies I may encounter due to keeping the relays under the dash instead of at the terminal blocks. I will still have voltage drop through the dimmer switch but due to the funkiness of the way the factory wired these cars that really only impacts the passenger side headlight when in country mode.

I really can't finalize anything until my new harness gets here but it is looking like I'll be able to use a standard harness configuration rerouted to a fuse block and relays that are either tucked up next to the hand brake or possibly near where the horn relay is. If I can use the hand brake location I can probably even clean up some of the mess under the dash as well as move some of the wires out of harms way should the vent leak.

Jeff

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To simplify this whole process I would use only 2 relays (or possibly one depending on the design) and only for the high beams because I believe they draw more current than the low beams. You should be good with the up-gauged wiring in your new harness.

Joe, BCA 33493

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In my early reading I found time and again that you want to put the relay as near as possible to the thing that will consume it. That is what led me to originally wanting to put them on the terminal blocks. The challenge in hiding them up there wasn't too appealing but after I realized how funky the factory wiring is I realized it would require me to either modify the stock harness configuration or put 2 relays on each side of the car (total of 4) as well as run a 10 gauge power line to each of the sides of the car. Hmm... I just had a flash of a thought. Those headlights are awful big and I wonder if I could place the relays inside them?

Grant, did you mean that to be effective I'd need separate relays for both low and high on both sides of the car for a total of 4 relays? Perhaps I missed something but I haven't run across anything to suggest that before. Then again, I started this thread because I was looking for more details on how others did this because that kind of detail wasn't in my previous reading.

Jeff

I must admit Jeff, the thought crossed my mind to hide them up there! The writeup I saw on adding relays was quite specific on the most effective location as being as close to the bulbs as possible, and yes, for low and high beam, you'd need 4 relays, 2 per side to make it work. Our old 1935 Chrysler was done this way, and it was a popular mod back in the day!

Cheers

Grant

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