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How to Install Headlight Relays

Submitted By: TaZMaNiaK Date: November 16, 2008, 11:55:29 PM Views: 13078

I wrote that nearly 10 years ago, so I don't really remember, but lets say this is what's missing.. I'm going to add details about using relay sockets for neatness. I'm also going to modify Step 3 per a suggestion from moparmike72, and Step 8 per a suggestion from MoabION. It won't let me edit it, so mods, please copy/paste this in where it belongs..

Parts list:

(1) Roll (20 feet) of red 10ga stranded wire (you can use two different colors if you wish)
(1) Package of small split loom tubing, or 1 roll of friction tape (NOT ELECTRICAL TAPE)
(2) HEAVY DUTY sockets for H4/9003 (they must have 14ga or larger wires)
(1) H4/9003 male pigtail adapter
(2) Bosch style, 4 or 5 pin, 30A/40A automotive relays
(2) 4 or 5 pin relay sockets (OPTIONAL but RECOMMENDED - MUST have minimum 12ga leads on pins 30 and 87)
(2) 30A inline fuse holders
(1) 6ga or 4ga copper cable lug
(3) BLUE ring terminals for 14ga wire, with #10 holes
(4) BLUE .250 FULLY INSULATED female spade terminals (ONLY IF RELAY SOCKETS ARE NOT USED)
(4) YELLOW .250 FULLY INSULATED female spade terminals (ONLY IF RELAY SOCKETS ARE NOT USED)
Zipties, glue-filled (AKA self-sealing) heat shrink tubing, solder, soldering gun (an iron will not be powerful enough)

Step 1

Cut two lengths of the #10 wire long enough to go from one headlight to the other (marking one of them if you don't use different colors). Insert them into the split-loom tubing or wrap them in friction tape (this is the same tape that is used on the stock harness) then lay it into the truck. At the passenger side, install one of the new headlight sockets (connect the LOW and HIGH wires only), using solder and heat shrink tubing to seal the joint. Install a ring terminal on the GROUND wire

DO NOT USE UNSEALED CRIMP CONNECTORS UNDER THE HOOD. THEY WILL CORRODE AND ROT - I LEARNED THIS THE HARD WAY!

The only crimp connectors suitable for under hood use are made by 3M, and have glue-filled heat shrink tubing already attached. When you shrink the tubing, the glue weather-seals the connection so it doesn't rot.

Step 2

At the driver's side, connect the other new headlight socket to the same colored wires as the other side. Again, install a ring terminal on the ground wire.

STEP 2A (IF YOU ARE USING RELAY SOCKETS, SKIP TO STEP 2B)

Then connect a small (6") pigtail of 10ga wire to each pair, and solder/heatshrink the connection. At the end of each pigtail, install one of the YELLOW spade terminals. These will connect directly to the spades on the relay. Then, take two 6" pieces of 16ga wire, twist one end together, and install a ring terminal. Install a BLUE spade terminal on the loose ends. These will connect to the relay grounds. (NOW SKIP TO STEP 3)

STEP 2B (ONLY IF YOU ARE USING RELAY SOCKETS)

Then connect the new HIGH BEAM wires to the lead coming from pin 87 of the high beam relay, solder and heatshrink the connection. Do the same thing for the new LOW BEAM wires. Take the Pin 85 leads from both relay sockets, twist them together, and install a ring terminal. This will be the relay grounds.

Step 3

Disconnect the old headlight plugs and plug in the new ones (Fill the socket terminals with bulb grease first, and if necessary, sand the bulb prongs to get rid of any corrosion.). Take the new MALE headlight pigtail, and cut off the ground lead (we are not using it).

If you are using relay sockets, connect the HIGH BEAM lead (FACTORY RED) to the Pin 86 lead of the HIGH BEAM RELAY, and the LOW BEAM lead (FACTORY BLACK/RED) to Pin 86 of the LOW BEAM RELAY. Solder and heat shrink your connections.

If you are not using relay sockets, attach BLUE spade terminals to the pigtail wires.

Plug the new male pigtail into the DRIVER'S factory headlight socket.

Step 4. Drill a 1/8" hole for each ground ring as shown. Sand down to bare metal and screw the rings down with #10 screws. The ring with 2 spades coming out is ground for the relays. Also drill 1/8" mounting holes for the relays.

Step 5

Run two lengths of 10ga wire from the relay location to the positive battery terminal. (Ziptie or wrap them together for neatness) These will be your relay feeds. If you are using relay sockets, attach one to the Pin 30 wire of each socket. If you are NOT using sockets, install a YELLOW spade terminal on each wire.

Step 6. Wire up the relays. They get connected as follows:

High Beam Relay

Terminal 30: Battery

Terminal 87: BLUE headlight wires

Terminal 85: Ground

Terminal 86: RED wire from factory wiring

Low Beam Relay

Terminal 30: Battery

Terminal 87: WHITE headlight wires

Terminal 85: Ground

Terminal 86: BLACK/RED wire from factory wiring

Terminal 87a (if present) is not used in either relay.

Step 7. Mount the relays using #10 screws and ziptie your wiring to make it look neat.

Step 8

Cut the battery end of the 10ga leads to length. Install a 10ga (30A) fuse holder on each lead, using solder and heat shrink to seal the connection. From the other leads from the fuse holders strip 1" of insulation and firmly twist them together. Install the 6 or 4ga battery lug, using a hammer and punch to crimp it securely on the wires. This crimp CAN be left unsoldered, but it still makes for a better connection if you do. You will need to heat the lug with a torch though.

(The purpose behind the individual fuses is so that if a fuse blows at night, you will still have the other beam.)

If necessary, drill the hole out to 3/8". Remove the nut from the positive clamp bolt, slip the lug on, and tighten the nut.

That's it! Turn on the headlights and flip between high and low to make sure they all work. Go for a drive at night and see how much brighter the lights are! I also highly recommend the Sylvania X-tra Vision or SilverStar bulbs next time you have to replace. I use the X-tra Vision and they are a LOT whiter than regular halogens. They also don't give you that "black hole" 10 ft in front of you like every other bulb does. I haven't seen the SilverStars yet, but they are supposed to be even better.

Rating:

by 3 members.

Comments
moparmike72 Jr. Member Offline Gender: Posts: 721	December 28, 2011, 01:36:52 PM I wouldn't cut the old headlight connector off the original harness, I would put a couple of blade terminals on the relay trigger wires and plug them in there. That way,with the original wire harness left intact, the headlight system can be reverted back to stock when you sell the truck someday. You can move the relay harness to your next rig and your old truck's new won't be scratching his head, saying "what the hell is all this for?".
MoabION Full Member Offline Gender: Posts: 1160 Moab Rocks!!	September 23, 2011, 01:41:58 AM I agree that this is a great idea. Really takes the load off the weak headlight switch. I do recommend installing a 30 Amp circuit breaker between the battery and the relays.
pir2 Site Assistant Full Member Offline Gender: Posts: 2203 A Long Time Dodge Boy	April 3, 2010, 07:16:01 AM Where is step one and two?

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