Headlight Relay wiring? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Project1970 · 11-24-2002, 09:13 PM

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* · 11-24-2002, 10:35 PM

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 · 11-25-2002, 12:20 AM

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

Lippyp · 11-25-2002, 06:06 AM

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

8mag · 11-25-2002, 08:43 AM

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

TERRYP · 11-25-2002, 04:17 PM

this moght help

XXL · 11-25-2002, 04:48 PM

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 · 11-28-2002, 10:40 AM

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 · 11-28-2002, 11:42 AM

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 · 11-28-2002, 02:23 PM

Quote:

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 · 11-28-2002, 03:58 PM

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

jiggs · 11-29-2002, 03:51 AM

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 · 11-29-2002, 09:07 AM

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

Longhorn Man · 11-29-2002, 10:56 AM

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.

11-24-2002, 09:13 PM	#1
Project1970 14.1 @ 96MPH Join Date: Jul 2001 Location: Mesa, AZ Posts: 2,811	Headlight Relay wiring? 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. __________________ Project1970 - LS1 Swap Complete!

11-24-2002, 10:35 PM	#2
Piston Account Suspended Join Date: Oct 2002 Location: Olathe, KS Posts: 2,301	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) Last edited by Piston; 11-24-2002 at 10:37 PM.

11-25-2002, 06:06 AM	#4
Lippyp English Chevy Owner Join Date: May 2002 Location: Shropshire, UK/ Lot, France Posts: 1,848	As I'm a bit of an idiot when it comes to wiring diagrams, what colour is the original wire into the headlight? __________________ Phil '67 C10 long fleet. 350/TH350, 4 bbl Carter, K&N, Dual exhaust, loads of stuff coming soon 2001 S10 Blazer Daily Driver, bone stock 4 door 4x4 with manual transmission

11-25-2002, 08:43 AM	#5
8mag Registered User Join Date: Jun 2001 Location: nampa idaho,usa Posts: 92	how much difference does it make if your running wagner halogen headlights. __________________ 1972 3/4 4x4,14bolt locker rear, dana44 lock right front, sm465, sb 400, blazer tank,dual batterys,3"lift,32-9.00-16 super swampers daily driver other trucks 1972 1 ton dually 4x4,454 4 spd,,235-85-16, flat bed front and rear winches, rear gas tank and under bed gun safe.tilt wheel

11-25-2002, 04:17 PM	#6
TERRYP GYRO GEARLOOSE Join Date: Jun 2000 Location: Nevada City, CAEverett, WA Posts: 361	this moght help Attached Images __________________ Nevada City, CA Everett, Washington 57 3/4 rat, 235, 3spd 66 C-10 Panel, SWB. 350 from '68, 200R4 tranny, 3.07 rear ratio, restoring 68 C10 LWB 350 4spd, 4.56 rear dump runner 82 Camaro, 305, THM-200-R4 84 Monte Carlo 305 TH350, land tuna 85 Tercel SW, snow runner DISGRACED OUTLAW MEMBER OF THE DRUM BRAKE CLUB

11-25-2002, 12:20 AM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Woo hooo....I been planning on this too, but was unsure of the wireing. Thanks.

11-25-2002, 04:48 PM	#7
XXL Señor Member Join Date: May 2002 Location: Edge of the world Posts: 5,367	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 __________________ Craigslist \| ebay \| Engrishtees \| www.myattitudesucks.com \| Follow me on Twitter

11-28-2002, 10:40 AM	#8
XXL Señor Member Join Date: May 2002 Location: Edge of the world Posts: 5,367	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 Attached Images __________________ Craigslist \| ebay \| Engrishtees \| www.myattitudesucks.com \| Follow me on Twitter

11-28-2002, 11:42 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	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)

11-28-2002, 03:58 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Hmmm, good point on the weather thing...maybe I should rethink my mental schematics.

11-29-2002, 03:51 AM	#12
jiggs poker face Join Date: Jul 2002 Location: Saskatoon, Saskatchewan Posts: 218	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. __________________ If you could kick the person in the *ss responsible for most of your trouble, you wouldn't sit for a month.

11-29-2002, 09:07 AM	#13
8mag Registered User Join Date: Jun 2001 Location: nampa idaho,usa Posts: 92	how much improvement with stock headlamps............. __________________ 1972 3/4 4x4,14bolt locker rear, dana44 lock right front, sm465, sb 400, blazer tank,dual batterys,3"lift,32-9.00-16 super swampers daily driver other trucks 1972 1 ton dually 4x4,454 4 spd,,235-85-16, flat bed front and rear winches, rear gas tank and under bed gun safe.tilt wheel

11-29-2002, 10:56 AM	#14
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	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.



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