In deer country it helps to be able to see far ahead at night using high power driving lights, but I found it to be a pain trying to turn off the driving lights every time oncoming traffic suddenly appeared. So the solution would be to wire in an extra relay to turn on the driving light relay only when the high beams are on (and an extra switch to prevent this from happening and keep the driving lights off w/ high beams on). The problem (on 1st gens at least, don't know about others) comes in when you try to figure out how to do this with the "negative switched" high beams - when the headlights are turned on, there is voltage present at both high and low beam bulbs, the headlight dip switch just gives one or the other a ground to turn it on.

Here's the factory wiring

the headlight relay is turned on by the rotating part of the switch and high/low beam is controlled by giving or removing ground directly through the headlight dip switch (high beam switch). 12V+ is at the top of the pic and ground is at the bottom

Here's the wiring I came up with to solve this

The driving lights are currently wired "normal" with a relay providing power for the lights and a switch to turn on the relay - I can turn them on anytime the ignition switch is turned on. We want to bypass the regular switch (SW1) and provide power to the driving light relay (RELAY 1) to turn them on. The High Beam switch can provide a ground for RELAY 2, so we just need to supply power. When the low beams are switched off and highs turned on, there is power present on the low beam circuit (no ground) - this is where we'll get power since it is only on with the headlights on and low beams off.

The relay wiring isn't too difficult. I used a RadioShack relay p/n 275-248, rated for 12VDC and 10Amps which will be more than adequate to power the driving light relay. Here's the back of the package which shows the relay wiring diagram

and how I wired the relay

the red wire supplies power to the relay coil and load side of the relay (NO terminal). The black wire will get connected to the high beam wire (with a switch inline). The white wire goes to RELAY 1, or better yet the wire from our driving light switch (SW1) which leads to RELAY 1.

on my '88 4runner, these were the 2 wires I soldered my connections to. In my install I attached the wires to the backside of the connector, or on the wire harness side (as opposed to the headlight switch side)


Now I can turn my driving lights on anytime I want - or have them come on automatically with my high beams. To wire a set of fog lights to somce on automatically with the low beams it would just be a matter of wiring everything the same, but switching the Red/Yellow and Red/Green wire connections (R/Y powering the relay, R/G providing a ground for the relay coil