Headlight Loom upgrade

This is a good upgrade even for stock head lights but even more so for those who run higher wattage globes ( bulbs in the US ). Running higher watt globes on stock wiring will cause the wiring etc to over heat and cause the lights to black out! Not what you want when rounding a bend in the middle of the night at speed. Consider these facts on voltage drop. A Halogen headlamp is rated to produce 100 % of its rated light output at 13.5V. When voltage at the headlamp drops by 5 % to 12.82V the light output drops to 83 % of normal. When voltage drops by 10 % to 12.15V the light output drops to just 67 % of what it ought to be. A mere 1.35V of lost voltage has robbed you of 33 % of your light output. And it gets worse as voltage is further reduced. These figures come from a leading headlamp manufacturer and this site. This setup will allow the use of 170/100W globes to be used safely. You can use this setup for any brand of vehicle as you don't even need to know anything about the wiring setup so long as they run H4 globes as all the switching is run from the plugs at the back of the headlight. Even other globe types can still use this setup so long as you plug your switch wires to trigger the relays into the high and low beam terminals.

Item	Amount	Description
	520 cm	You need the red 6 mm wire for supplying both the relays and the headlights high and low beam. 6 mm wire falls closest to 10 AWG wire and is rated to carry 50 amps.
	260 cm	This is black 6 mm wire to supply the ground for the headlights. ( 10 AWG ) Use only automotive wire for all connections or if in a salt area, marine boat wire is even better.
	160 cm	This wire is only used to ground the relay and as a switch wire from the old headlight plug. I used 2.5 mm wire which is around14 AWG.
	4 of	To fit the 6 mm or 10 AWG wire to the battery terminals for ground and to the front of the engine fuse box for positive. Check your batter clamp bolts size. Mine were 1/4"
	6 of	To connect the 6 mm or 10 AWG wire to the relays
	4 of	To connect the 2.5 or 14 AWG wire to the relay for the switch and ground wires.
	2 of	To connect the 2.5 or 14 AWG wire to the old headlight plug for the relay switch wires. Can also use a male H4 plug to make it even neater. http://www.rallylights.com/detail.aspx?ID=1421
	2 of	To connect the 2.5 or 14 AWG wire to ground from the relays
	2 of	Waterproof inline blade fuse holders and 30 amp fuses ( depends on the wattage of bulbs used ).
	2 of	New H4 headlight plugs. Buy the ones without wires already on them from a auto electrician or if in the USA, http://www.comagination.com/ . Also here in the USA, http://www.rallylights.com/detail.aspx?ID=1242
	2 of	Used one 40 amp for the high beam and one 30 amp for the low beam. It makes it easier to identify them but even a pair of 30 amp ones are enough for up to 130 watts with still some head room. If you can, buy them with 5 pins ( 2x pin 87 for left and right headlight connections ) NAPA #AR274 Otherwise just put both wires together into the one spade terminal. Or as I have done since, two relays for each headlight, ( one for hi and one for low per headlight ). That way more current and can only loose one high or low per headlight at a time if a relay fails or fuse blows.
	2 of	You need 3 meters of 13 mm or 1/2" split conduit and only 1/2 meter of 10 mm or 3/8" as well for the switch wires.

I started by wiring the relays. The black 30 amp relay on the left is for the low beams and the grey 40 amp one on the right is for the high. You can just use two 30 amp ones but like using a 40 amp one for the high beam to give plenty of head room for running 170w globes. If you are running 2 relays for each headlight, you will need to double up each one and run the switch wire to both pairs. Remember all wire lengths are based on the fact that you fit them exactly where I have and on a Jeep XJ Cherokee. If you choose another location for the relays all the measurements will have to change.

Wire A ( one for each relay ) above goes from pin 30 on the relay using a yellow female spade at one end, to power using a 1/4 ring terminal for the front of the fuse box at the other. This carries a 30 amp blade fuse holder with water proof cap and came complete with the 6 mm wire needed pre-assembled.

Wire B ( one for each relay ) runs from pin 85 to ground on inner guard panel. It is 2.5 mm wire 20 cms long with a blue female spade at the relay end and a ring terminal at the other to a ground screw.

Wire C runs from pin 86 to the old headlight plug low beam socket ( top most terminal on the plug ) using a blue male spade at one end and a blue female spade at the other for the relay. It is 2.5 mm wire ( 14 AWG ) 60 cms long.

Wire D runs from pin 86 on the grey relay to the high beam terminal on the old headlight plug using a blue male spade at one end and a blue female spade at the relay end. It is 2.5 mm wire ( 14 AWG ) 60 cms long.

Assemble the headlight plugs as shown above right. You will need three wires 60 cms long for the right headlight and three 200 cms long wires for the left side. Two red wires each side with yellow female spade terminals at the relay end and the new headlight plugs female push in terminals at the other. One black for each side with headlight plugs female push in terminals at one end and yellow ring terminals to suit the negative battery terminal bolt at the other. I soldered and crimped them before pushing them into the holders headlight holders.

Now time to join the relays to the headlight plugs. Wires not marked are those already shown above in the first photos.

Wire E runs from the right headlight plug to pin 87 on the grey high beam relay and is 6 mm or 10 AWG wire 60 cms long.

Wire F runs from the right headlight plug to pin 87 on the black low beam relay and is 6 mm or 10 AWG wire 60 cms long.

Wire G goes from the right headlight plug to ground on the battery and is 6 mm or 10 AWG wire 60 cms long.

Wire H runs from the left headlight plug to pin 87 on the grey high beam relay and is 6 mm or 10 AWG wire 200 cms long.

Wire I runs from the left headlight plug to pin 87 on the black low beam relay and is 6 mm or 10 AWG wire 200 cms long.

Wire J runs from the left headlight plug to ground on the battery and is 6 mm or 10 AWG wire 200 cms long.

I encased the wire in split conduit to tidy in all up as well as making it easier to run keeping it together and protected. The three thick wires together in the 13 mm conduit for both left and right headlights and the two switch wires together in a 10 mm one. I mounted the relays on the support bracket for the fuse box. You can see also how the relay grounds ( pin 85 ) use the fixing bolt of the same bracket as well.

The two power supply wires from the relays ( pin 30 ) attached to the front of the fuse box where the power supply from the battery is fixed. The cover slips back over nicely leaving them protected. The two headlight ground wires from the plugs attached directly to the battery terminal making sure the best possible supply. A body ground is not as good for this many amps.

The photo above shows the switch wire connections to the old headlight plug. The red wire ( wire C from the top photo ) goes in the top most terminal and then to the black low beam relay on pin 86. The purple wire ( wire D from the top photo ) goes in the left terminal and goes to pin 86 on the grey high beam relay. To run the loom across to the other headlight I placed it behind the grill support frame as shown. It tucked in nicely between that and the auto cooler brackets as shown with the left cooler bracket done and right cooler bracket still not to show where it runs.

Even though the above photos have different exposures, they really were that different with the left photo showing the new wiring and the right one still plugged into the old wiring. They were much brighter and a whiter than before now that there is no voltage drop. These were running 130/90W globes and if left on high beam for too long they would cut out all together. Now no such problem happens.

I have also been made aware that on some models with day time running lights ( DRL ) that it can cause problems. The easiest way to fix it is to disconnect the DRL module. This will though stop the high bean light from coming on so to get that to work, just jump the no.1 and no.4 terminals on the plug from the DRL whose plug is pictured below to suit 90-98 years.