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Automotive Service Home Help

Parts needed:

  • 1 relay
  • 8 feet wire


This is a simple design to turn off headlights when ignition is switch OFF or on ACC. When ignition is switch ON and headlights are turned on, the headlights will stay on even during driving, however, headlights will turn off automatically while cranking.

How it works:

The underdash fuse, which is used for wipers or etc.. carries 12 V power when ignition is ON. That power will flow to the relay energizing the relay and allowing the contacts from the headlights underhood fuse to flow through to your headlights high beam, low beam and parking lights. A sample relay (at right) shows the pin for the relay. If you picked up a relay and don't which pin is which, simply attach 12 V battery positive terminal to one of the pin and negative battery terminal the anyone of the pin until you hear a click. Keep trying, or use a ohm meter to find the correct pin.

If you don't know which sockets to use, for example upper or lower sockets, keep trying either sockets until your project works. Caution: do not send ground into any fuse sockets.

I don't want to use a relay

Main Relay

FIX: how to repair the main relay-all models.

Don't know what ignition positions or wire colors means? Click here

Fluid Replacement

This represents the wire that you'll  connect from under dash fuse to the underhood fuse.
 This is the movement found inside an ordinary 30 Amp relay used in the above layout.
 If you don't have a relay, and don't want to use one in your project, click here.
Automotive Service Home Help
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