There are two conflicting ways to wire up a standard H4 headlight globe (and I can't think of why this has happened). Some people describe the high beam on the base of the "U", others say that pin is the low beam ... first, let's make sure we're looking at the globe correctly.
Pick up a H4 globe and face the bulb part away from you so you're looking at the pins. Turn it so that the pins form a "U" shape. The pin on your left should be HIGH BEAM. The pin at the bottom of the "U" should be LOW BEAM. The pin on the right should be "common" or "ground".
With a pair of alligator leads, try this: attach one lead to the NEGATIVE battery terminal and attach the other end to the "common" pin. Now attach the other lead to the positive terminal and touch the opposite (high beam) pin. Inside the globe, the filament closest to the tip (not the one with the shield) should light up. Touch the other - low beam - pin and the filament with the shield should light up. That's how it's supposed to work.
Now check - when your headlights are OFF - that you have negative continuity (battery negative to common pin, use a multimeter testing for resistance, should not see more than a couple of ohms). Now change to volts on the multimeter (50V range), turn on low beam and identify which wire is presenting 12V. This should be low beam. If yours is wired incorrectly you now know which one should be which!
As for the light bar (or any driving lights) - you can wire them up a number of different ways. My personal preference is like this:
One heavy (40A) red wire from battery positive to a 20A fuse to pin 30 of a 12V relay.
One heavy (40A) black wire from battery negative to light bar NEGATIVE (usually black).
One light (10A) blue wire from high beam to pin 85.
One heavy (40A) red wire from pin 87 to the light bar POSITIVE (usually red).
There's one more and this is my tricky bit. Connect a thin (10A is enough) black wire to a bolt under the dash and connect the other end to one pole of a SPST switch you can put in your dash. Connect the other pole of this switch with another length of thin black wire, through the firewall and up to the relay and connect it to pin 86.
Operation explained:
When the SPST switch is OFF, low beam is low beam and high beam is high beam and the light bar is OFF all the time.
When the SPST switch is ON, low beam is low beam and the light bar is OFF. When high beam is activated, the lightbar comes on because power goes from the high beam wire to pin 85, which energises the relay because it's now earthed through pin 86 and the SPST switch inside. Energised, the relay passes power from the battery through the 20A fuse to the light bar directly.
That's how it's supposed to be done, with minimal wiring.
