Headlight Relay Mod

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

MrMarty51

Full Access Member
Joined
Oct 25, 2012
Posts
7,793
Reaction score
10,018
Location
Eastern Montana
First Name
Martin
Truck Year
1978
Truck Model
K20
Engine Size
400
First of all, I guess it would greatly help if a person understood what a relay is and how they work.
Here is a page, a simple tutorial for understanding the theory of how the automotive relay works and what each terminals job is. it is only one page with large letter writing and a few diagrams of how to wire the relay in most any application.
I would first read this before attempting to wire in Your own relay. Once the basics is understood it will take "ALL OF THE FRIGHT" out of wiring in Your own system.
One more thing, when tapping into a wire, through a splice, always stagger Your splices to keep from creating one great big knot of splices in one spot.
http://www.eurekaboy.com/f250/relay101.htm

Here is a pic. of the relay I installed on My 93. There is a lot of talk about diodes and such but just scroll down a bit and You`ll find the pics.
http://www.gmsquarebody.com/forum/showthread.php?t=5966&highlight=headlamp+diode
What I did was to tap into the bright headlamps wire, on the passenger side and then run a wire from the tap to where I was going to have My relay mounted, or hung.
Wire in the relay as prescribed and use the bright tapped in wire for the "Signal" wire, on the other side of the relay will be another wire run to ground.
Hook another wire into one of the battery terminal lugs and hook that, through a 20 amp fuse to the battery or + side of the relay, across the relay, from the + wire, hook that pigtail/terminal to another wire that You have run back to the headlamps wire harness and hook that wire into the "DIM" lights harness.
Now, when the headlamps are on dim, only the dim will light up.
When the headlamps are turned onto the "Bright" mode, a signal will be sent to the relay, through the switch incorporated in the relay to the ground turning the switch on.
When the switch is turned on, it will run power through the switch and back to the dim lamps bulbs turning them on while the bright lights is lit up.
If You have any questions, please post them up.
I hope this all helps and that You can/will wire in Your own system. That will be a very nice beginning, in the knowledge of automotive wiring for You.
 
Last edited:

82chevy350

Full Access Member
Joined
Jul 30, 2010
Posts
775
Reaction score
51
Location
Van Buren, AR
First Name
Joey
Truck Year
1982, 1976
Truck Model
C10, K10, K5
Engine Size
350, 350
Oh I have an idea already im in electrical II in college. id rather have a bunch of stuff have a relay which is why im thinking about converting to a newer fuse block system.
 

MrMarty51

Full Access Member
Joined
Oct 25, 2012
Posts
7,793
Reaction score
10,018
Location
Eastern Montana
First Name
Martin
Truck Year
1978
Truck Model
K20
Engine Size
400
Oh I have an idea already im in electrical II in college. id rather have a bunch of stuff have a relay which is why im thinking about converting to a newer fuse block system.

And after finished will probably help to get more credits towards the degree too. :deal: LOL
 

Green79Scottsdale

Full Access Member
Joined
Aug 8, 2010
Posts
2,834
Reaction score
7,487
Location
G.R. - MI
First Name
Bob
Truck Year
1979
Truck Model
K20
Engine Size
400
I am not very electrical smart, so it was easier for me to buy one. The one I got came with all the relay's and stuff that new vehicles utilize. There was no major re-working of the wiring system to a new fuse block system. All it does is use the old headlight on and off to switch the relay's to provide power.
 

da_raabi

Trailer Park Supervisor
Joined
Aug 7, 2013
Posts
1,403
Reaction score
901
Location
FloriDUH
First Name
Adam
Truck Year
1986
Truck Model
c30
Engine Size
454
I have a printed copy of the schematic I got from an older truck (I think I got it on the 67-72 forums), I'll see if I can find and upload it.
 

MrMarty51

Full Access Member
Joined
Oct 25, 2012
Posts
7,793
Reaction score
10,018
Location
Eastern Montana
First Name
Martin
Truck Year
1978
Truck Model
K20
Engine Size
400
:favorites13: here, have a beeer, :popcorn: some popcorn toooo.
 
Last edited:

MrMarty51

Full Access Member
Joined
Oct 25, 2012
Posts
7,793
Reaction score
10,018
Location
Eastern Montana
First Name
Martin
Truck Year
1978
Truck Model
K20
Engine Size
400
Some good stuff right there 8T
I saved that image to the desktop, stuffed it in My GM wiring folder.
Thank You very much.
 
Last edited:

89Suburban

Supporting Member
Supporting Member
Joined
Dec 7, 2010
Posts
24,772
Reaction score
6,631
Location
Southeast PA
First Name
Paw Paw
Truck Year
2007
Truck Model
Chevrolet Tahoe LT
Engine Size
5.3, 4WD
Nice diagram
 

Forum statistics

Threads
44,152
Posts
950,445
Members
36,268
Latest member
JUKA
Top