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Brighter Lights - Add Relays

Bright Headlights? Add Relays

The Problem:

The stock wire headlight wiring is quite small (#18)
and it follows a serpentine-like path from the battery to the
headlight switch, down to the high/low switch and then back thru the
engine compartment to the headlights. The voltage drop along this
path is not negligible, so the lights only get maybe
9-12 volts instead of the 13-14 they should have.
You also can get flickering from the headlight thermal breaker tripping,
which eventually dies from the well known "flashing Ford headlights" syndrome.

The Symptoms:

You just put nice new halogens in, but your lights still aren't that
bright. You see lots of other cars on the road with plain old
halogens that are lots brighter and whiter than Yours and it really
bums You out. Higher wattage bulbs don't help because they draw more
current which causes more voltage drop in the wiring so the fatter
bulbs get even LESS voltage and ain't any brighter! )-:

The Solution:

Headlight relays!
With relays, the headlight switch, dimmer switch, and stock wiring only
have to handle enough current to drive a relay coil, less than 1/4 of
an Amp instead of the 10-12Amps they normally have to carry.
The relays are located near the battery, with nice short heavy gauge wire
connecting them to the headlights.

Required materials:

  • 2 relays
  • 25' of #14 stranded wire
  • 8' of #18 wire
  • A pile of 1/4" female spade lug crimp connectors
  • A couple butt type crimp connectors
  • ring lugs
  • some heat shrink tubing
  • wire strippers and crimpers
  • a soldering iron and solder
  • electrical tape

NOTE: The soldering iron and solder is optional depending on how You approach
the headlight connector. Do not attempt this without the beer.

The relays:

I started with 2 "bosch style" relays. These are a black plastic cube,
roughly 1"x1"x1" with a mounting tab on the top and five 1/4" push-lugs
on the bottom. They are rated at 20 amps, are compact, reliable, readily
available, and dirt cheap. I get mine from Kragens for under $3 each.
I find them in the "lighting" section, with the fog lights and driving
lights and stuff. I've seen/bought them at several of the chain stores.

These relays are reproduced by a zillion manufacturers now, but *always*
have the terminals numbered with the origional Bosch designations.

 #85 = relay coil side A
 #86 = relay coil side B
 #30 = relay contact "hot side"
 #87 = relay contact "load side" (there are 2 #87's on these, conected
       together internally, so You can plug 2 wires on the load side.)

The Procedure:

Start by disconnecting the battery so nothing "bad" can happen while
You are mucking about in the electrics...
I drilled 2 holes in the fender, between the battery and the starter
relay and screwed the relays in place. Label one of them "highbeam"
and one "lowbeam".

I already had a nice fuse block mounted in the vicinity with extra
slots available, so I used it.
The rest of You will need to mount a 2-fuse block somewhere near the

Connect wires from one end of each fuse holder to the battery using
some #14 wire. The big terminal on the starter relay is a good place
to attach the battery end of these 2 wires.

Connect the other end of a fuse holder to one of the "contact"
terminals on the "lowbeam" relay using #14 wire. If You use the bosch
type relay, the appropriate terminal will be labeled "30".
Connect the other fuse holder to the "highbeam" relay, just like the
first one.

Connect a short length of #18 wire to one of the coil terminals on
the lowbeam relay. On the Bosch style relay this will be "86".
Ground the other end of this wire to a suitable, clean chassis ground.
Repeat for the highbeam relay, grounding coil terminal "86"

Now take out the drivers side headlight. Remove the trim piece around
the headlight bucket so You've got some room to work.
Remove the bulb from the connector and cut the wires (red, green, and
black) loose from the back of the connector. Leave an inch or 2 of wire
on the back of the connector so You have some options when we get to a
later step...

Tape up the cut ends of the 2 wires that dangle from the harness.
(red and green) We Aren't going to use them anymore, but they will still
be hot when the lights are on, so make sure they're insulated and can't
get in trouble.
Unscrew the black ground wire from the back of the bucket.

Now You get to decide how to handle the bulb connector.
I see 3 choices:

  1. Reuse the old connector, crimping or soldering a #14 wire onto each stub of #18 wire left on the back of the connector and insulating with shrinktube/tape.
  2. Buy new headlight connectors, available at the parts store and crimp or solder Your #14 wires onto these.
  3. Pop the spade lugs out of the old connector, cut the wires off and solder Your #14 wires directly to the old lugs, insulate with heatshrink and pop them back into the connector body.

I chose option #3 as being the best for me...

Once You've decided, attach a #14 wire to the high beam terminal (red)
and another to the lowbeam terminal (green) of the connector.
Make them long enough to route nicely from the headlight bucket to the
relays, plus enough extra to get the light out easily for servicing...
Attach a #14 wire to the ground terminal (black of the connector. This
one only needs to be a foot long. Put a ring lug on the other end of the
ground wire and ground it in the origional location. don't forget to clean
the metal all bright and shiny first. Smear a little silicone grease on
the metal to prevent rust would be nice too..
Route the wires up to the relays, keep it neat and use some tie-wraps
to keep things secure. Now You can put the light back in place.
Oh wait, if You put some silicone grease in the connector for the back
of the light, You'll avoid trouble later.. Now put the light in.

O.K, so now You've got 2 #14 wires from the left headlight up to the
relays. put a 1/4" crimp lug on each wire and plug the highbeam wire
onto the unused contact terminal on the high beam relay. On the
Bosch style relay this is terminal "87". There are actually 2 terminal
"87"'s on the relay. Use either one, they are connected together

Now connect the low beam wire to the terminal "87" on the lowbeam relay.

O.K, so You've got the drivers side light grounded and wired to the
relays #87 terminals with #14 wire and the light is back in, right?
Good, lets continue...

Pull out the passenger side light, and cut the connector loose from the
harness as before, but be carefull to leave the harness wires long
enough to connect some #18 wires to them. We're gonna use these to drive
our relay coils. So, crimp a #18 wire onto each of the 2 lighting
wires poking out of the harness (one red, one green) and route them up
to the relays. Connect the highbeam one (red) to the coil terminal on
the higbeam relay. On the Bosch style relay this is terminal "85".
Connect the lowbeam one (green) to the coil terminal "85" on the
lowbeam relay.

Now connect some #14 wires to the pass side headlight connectors, and
ground the black terminal and route the red and green ones to the
relays just like we did for the drivers side.
You remember how we did the drivers side right?

Hook the lowbeam wire to terminal "87" on the lowbeam relay, and the
highbeam wire to "87" on the highbeam relay.

Alright! that's all the wiring!
Silicone grease Your pass side headlight connector and put the bulb back
in and any trim back on. Make sure all Your wiring is secure and can't
get in trouble and then clean up Yer mess...

Now You can stick some 20 amp fuses in Your new fuse holders and hook the battery back up.

Test out Your new handywork and enjoy!

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