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Headlight Conversion Using Relays

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  • Headlight Conversion Using Relays

    Kenn Oie in Wisconsin asked me about retrofitting H4 headlamps in his Squarebird. H4 bulbs cast a lot more light but it comes at a cost of higher amperage (that our cars weren't designed for). Rather than overloading the headlight switch, we use the headlight switch to turn on relay coils. Then, the relay contacts carry all the load.

    The existing plug-in bullet connections are accessible at the fender apron. This is simply a matter of unplugging the HI/LO beam foot switch wires (at the front of the car) and jumper-ing them to turn on relay coils. The relay contacts control the headlight juice by completing the path from the battery to the existing bullet connectors.

    I got busy and identified our wire colors and applied them to this two-relay schematic. I put the instructions in the picture.

    Kenn suggested a great method for grounding the headlights/horns/parking lights, etc. He drills a hole and adds a long brass screw through the body panel then tightens it with a nut. The rest of the screw protruding beyond the nut is where all the ring terminals connect, then tighten with another nut. One of these on each side of the front will produce a solid ground. - Dave
    Attached Files
    My latest project:
    CLICK HERE to see my custom hydraulic roller 390 FE build.

    "We've got to pause and ask ourselves: How much clean air do we need?"
    --Lee Iacocca

    From: Royal Oak, Michigan

  • #2
    I did this on my '66 but used a two-in-one relay which made wiring just that little bit easier.

    Well worth the effort and as the relay is hidden by the windcreen washer bag it is a discrete modification.
    A Thunderbirder from the Land of the Long White Cloud.

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    • #3
      Some of my buddies put the relays in their Voltage Regulator can. Makes a clean job.
      If you think about it, the VR already has power and ground. Only four wires are needed; two 18ga., and two 14ga. - Dave
      My latest project:
      CLICK HERE to see my custom hydraulic roller 390 FE build.

      "We've got to pause and ask ourselves: How much clean air do we need?"
      --Lee Iacocca

      From: Royal Oak, Michigan

      Comment


      • #4
        Good diagram, just doubt check your relays don't have surge protection like a diode across 85 and 86.

        Otherwise you'll create a short circuit hooking them up as shown below. Always good practice to put earth (ground) to 85 for this reason and not 86. But as I stated just make sure your relay doesn't have surge protection and it will be fine

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        • #5
          Good point Michael, but these are 'ice cube relays' and none of mine have surge protection (because they really don't need it). The counter EMF (or fly-back voltage) is really nothing.

          If my example relay coils did have surge protection I would show it or note it.

          BTW, for proper surge protection I would NOT use a diode, in case someone hooks up the battery backwards. Don't laugh, I know a guy who unwittingly ran that way in his '55 Ford for years. In his case a diode would fry.

          Instead of a diode, I would use a small capacitor with series resistance. I've seen a small incandescent bulb (pilot light) used across the coil as well. Both methods snub power going in either direction.

          The 'bulb idea' indicates when the relay is energized while at the same time, incandescent bulbs are self-limiting resistors (in either direction of current flow).

          Your suggestion is well-founded for folks who buy relays with included diodes. In this case, I suggest using relays with no diodes, partly because Ford cars before 1956 had POSITIVE grounds. That would mess up a diode. My drawing will work with either negative ground or positive ground. My cousin John's Amphicars have 12-volt POS gnd., so they are out there. - Dave
          My latest project:
          CLICK HERE to see my custom hydraulic roller 390 FE build.

          "We've got to pause and ask ourselves: How much clean air do we need?"
          --Lee Iacocca

          From: Royal Oak, Michigan

          Comment

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