Headlight Relay wiring?

[Project1970]

I've seen this referenced a few times, using a relay to switch the headlights so as to get them full battery power...what relay(s) do I need for my GMC and how should I wire them up?

Just wondering, since this is probably a better (and more legally safe, heh) idea than wiring up all four to be low/highs. I do a LOT of my driving at night, so I do want as much light as I can realistically get.

[Piston]

Here's a wiring diagram with a bosch relay. This is the generic relay you can buy at any parts store for less than 10 bucks. It's a 30A relay which will be more than addiquate for the 12amps max your current headlights pull.

The toggle switch will now be your headlight switch. Take the wire going to your right headlight (mount the relay closest to the battery if you want so you reduce the amount of wiring you need). Be safe and add a inline fuse between the battery and the relay.

NOTE: You will use the top image (Switch with power on).
Pole connection:
86 - Ground
85 - old headlight wire output
30 - Battery w/fuse
87 - Headlight (Left)
87a - Headlight (Right)

[Longhorn Man]

Woo hooo....I been planning on this too, but was unsure of the wireing. Thanks.

[Lippyp]

As I'm a bit of an idiot when it comes to wiring diagrams, what colour is the original wire into the headlight?

[8mag]

how much difference does it make if your running wagner halogen headlights.

[TERRYP]

this moght help

[XXL]

You can do this while retaining your original headlight switch. Just catch the two 'outbound' wires... the ones going to the high and low beams. They may be green and tan (that's their colors on newer GM... I'm not in front of a truck to look to verify right now).

Just cut these wires in two and use 2 relays.

green (from switch) to pin 86
green (to headlight) to pin 87
ground to pin 85
B+ (fused!!!) to 30

do the same on the second relay with the tan wire (or whatever color it turns out to be).

This will give you full headlight switch functionality and full current to the lights.

BTW, I realize auto parts stores hawk Bosch relays (or cheapie knockoffs) for upwards of $10 but you should be able to pick them up for less than half that from a nice installer at a stereo store. They cost @$2.00 each in medium quantities, and I used to get them for $1.50 in 100 lot. Bosch is the "standard" but Potter & Brumfeld look the same, are just as reliable, and are reated at 40 amps (Bosch is rated at 30)... even though you'll be pulling less with your headlights.

Kenneth

[XXL]

Just as an update, I did verify the wire colors--

light green = high beam
tan = low beam
med. blue = B+ coming from dash switch

So, if you want to use your factory switch and get plenty of current to your headlights, grab the wires between the floor kick switch and the fuse box (they're in a nice little bundle all by themselves), and do the relays as I described above.

I've also started to (slowly) create some wiring diagrams for such things and will be posting them on my site. Here's the first quickie I did of the floor kick switch. Nothing fancy yet.

Kenneth

[Longhorn Man]

Instead of tapping into it there inside the cab, you would be better off doing it up by the headlamps themselves. This way, there would be less full voltage wire to lose power in.
I plan on mounting mine under the battery tray on the drivers side. (I have daul batterys in the Longhorn)

[XXL]

Originally posted by longhornmail
Instead of tapping into it there inside the cab, you would be better off doing it up by the headlamps themselves. This way, there would be less full voltage wire to lose power in.
I plan on mounting mine under the battery tray on the drivers side. (I have daul batterys in the Longhorn)

Do whichever works for you. The voltage drop for the 6' distance difference is less than 1/10th of a volt (ASSuming 14 gauge). By putting it inside the cab, you keep your metal-to-metal connectors on the relays out of the weather.

Kenneth

[Longhorn Man]

Hmmm, good point on the weather thing...maybe I should rethink my mental schematics.

[jiggs]

One thing that might help is to replace the headlights you have with good quality ones from Hella. The cut of the lense has a lot to do with how much light gets to the ground in front of you. You can also get large round headlights with the removable halogen bulb similar to new cars molded headlights. With the Hellas and some high wattage bulbs (100w high/ 55w low) and relays you will see a lot of improvement.

[8mag]

how much improvement with stock headlamps.............

[Longhorn Man]

Well, by stock headlamps, lets just asume you have normal halogon lamps...most do. (my GMC only has one non-halogon)
The diffirance is considerable...just get in a newer car that still has the sealed beam lamps....The camaro of a few years ago...S-10 of a few years ago.
It really is quite a bit. At night you can always tell an old vehicle coming up the roat towards you, becouse the headlights are yellow...even orange. They will glow white with this upgrade.