Repeat

[Bhelton]

I'm looking for thread on installing relays on headlights that has a complete parts list
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[luvbowties]

Originally Posted by Bhelton

I'm looking for thread on installing relays on headlights that has a complete parts list
Posted via Mobile Device

Maybe this will help. Merely adjust for quantities needed for 2 vs 4 lite system.


Headlight Relay System
Contributed by
Jolly Goodfellow
Craig Ueltzen
Scott Temple
For this 7 Year run of GMC Trucks, they have quad headlights. Upgrading to Halogens will overload
the old wiring found in these trucks. The pathetic wiring in most old cars is not really good
enough for the power draw of newer light bulbs. The old switches will start to fail too. This
method replaces the bulb's power with heavy wiring & relays in the engine compartment.
The original wiring under the dash remains untouched.

You will be needing two of these Bosch Relays for this Conversion. Any Good parts house can get
them for you. My self I plan on using the Heavy Duty 75 amp version. The smaller 15-20 amp
relay will work good in most cases, and are easier to find.
Turn on the lights & use a test light to find out which color wire goes to which bulb terminal. You will
need to know which is high beam & which is low beam. The dash indicator determines this later. Write
them down somewhere for future reference. Keep track of which wire goes to what bulb terminal also.
Cut the wires going to the headlight bulbs & reroute them to each Bosch Relay's terminal #85. Ground
each relay's terminal #86. This makes the headlight & dimmer switches control the relay with a very
low current draw. The old headlight & dimmer switches will keep going as long as the mechanical
action lasts, because arcing & heating of the switch contacts disappear with this project.
Turn on the lights & operate the dimmer switch. You should hear clicking noises from the relays. Watch
the dash indicator & leave the lights on high beam. Use a test light to see which relay is on. Mark
this relay "High beam." (You should already know which relay is high beam if you wrote the wire colors
down first). Use 12 gauge wire for the "High Beam" circuit & 14 gauge wire for "Low Beam". Use
non-insulated terminals & heat shink tubing on all connections. Connect a 12 gauge wire to terminal #30
of each Bosch Relay. Route the 12 gauge wire to a point with battery power, you should use some kind of
junction block & it should be powered by a 10 gauge wire from the battery "positive post". You may have
to purchase a battery terminal to enable the 10 gauge wire to attach to the battery itself. You also
might want to put a 40 amp curcit breaker close to the battery inline of the 10 gauge wire. An alternate
method is to tap onto the big wire(pos batt cable) going to the starter terminal. Don't power up the 10 gauge wire before
you get the relay end done, unless you like fireballs in your face should it touch the frame!
Run the 12/14-gauge wire for each circuit from each relay's terminal #87 to the head lamp Connectors. The best way
is to remove the old wires from the bulb sockets by pushing in the tab "ear" from the side to get the
connector out. On some sockets, you will need a skinny tool pushed down along the terminal from the front
of the socket to push down the tab. Solder the high/low wires to the connectors. Replace the ground wires
with 12 gauge while you're at it. This avoids the crappy looking 1" splice at the bulb socket. Be sure of
which terminal is what before you tear them apart. You can solder the wires together at the bulb, & run the
set to the other light bulb. You will have to split the wiring somewhere to feed the two sides. Scope out
the vehicle for the best way to route them.


I can send you a pic of the diagram if you PM me your email addy.

Sam