Light Trigger From Oil Pressure

The purpose of this modification is to prevent the headlight or lightbar lights from coming on until the engine is started. This will add little additional power to pull those decomps and crank the engine.

Some LC owners have resorted to putting some type of switch on the headlight which works good as long as you remember to turn it off when starting and turn it back on when you get ready to ride. Obviously at night one would quickly realize if the switch is on or not, but during the day that might be a different story.

How it works is pretty simple. The headlight gets power through the original wiring (and fusing) but the relay acts as an automatic switch. The relay will not close (and send power to the headlight) unless it is grounded. When the engine is not running (no oil pressure) the sending unit is open and the ground circuit is broken. The relay is open and no power goes to the lights. When the engine is running the sending unit closes sending the ground to the relay causing the relay to trip which turns on the headlights.

Other than basic tools you will need a socket designed to fit a sending unit, a driving light relay, and a normally open dual connection oil pressure sending unit, a pipe thread "T" block and some teflon tape. I got all this stuff from one auto parts store and the total cost was less than $20.00 (Image).

If you go to AutoZone and request a normally open oil pressure sending unit they will probably look at you like you just asked for a magneto-hydroshaft drive for a nuclear sub since they will have no way to look it up on their computer. The one I got was a "Standard" brand, model "PS135". If they can't cross-reference it, go to an old-fashioned parts store and they will probably know what you need.

I used a pipe "T" so that I could keep the original sending unit and light. I took my sending unit out and took it to the auto store to fit it, however, the threads are standard 1/8" pipe so there shouldn't be any problems finding the correct one. You will want a "T" with a male on one end, female on one side and female on the end (Image).

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