Headlight Wire Harness Upgrade

Tech information furnished by Wayne Tangen

Headlamp wiring harness parts list
By: Wayne Tangen
Assisted by: Dan Moeller
I used the following sources based on best compatibility with design, and convenience of source:

Newark Electronics: (ordered online)
Relay, Tyco VF4A-15F11-S01 - qty. 3 - P/N 27C6195 - $3.85 ea.
Relay socket, Tyco VCF4-1002 - qty. 3 - P/N 90F8247 - $1.25 ea.
Relay terminal, 10 gauge, Tyco 26A1348C - qty. 7 - P/N 50F1000 - $0.11 ea. - order spares.
Relay terminal, 14 gauge, Tyco 26A1348B - qty. 6 - P/N 50F999 - $0.15 ea. - order spares.
Inline fuse holder, ATO, 12-gauge wire, Littelfuse FHAC002 - qty. 2 - P/N 95F856 - $2.48 ea.
Resistor, 20 ohm, 25 W, Vishay/Dale RH-25 - qty. 1 - P/N 01F9766 - $2.45.
(Note: Newark charges $5 handling on orders under $25. My order was over that, and they did not even charge me shipping.)

Auto parts store: (I used Schuck's)
Headlamp connector - qty. 5 - $2.19 ea.
Fuses - 15 and 30 Amp ATO/ATC - qty. 2 ea.
Dielectric grease.

Radio Shack:
Inline fuse holder, ATC/ATO, 10-gauge wire - qty. 2 - P/N 270-1234 - $2.19 ea.
Ring terminals for 10-gauge wire and 5/16" post - qty. 4 (in 2 packs) - P/N 640-3120 - $1.69 ea. pack.
(These are sturdier than what I saw at auto-parts stores. A similar terminal could be ordered from Newark.)
Ring terminal for 16-gauge wire and 1/4" post - qty. 1 - included in pack above.
1N5404 diode - qty. 1 - P/N 276-1144 - $1.49.
(Could be ordered from Newark.)

Misc. procurements:
Wire, 10, 12, 16 gauge, 105 deg. C rated.
Quick-disconnect tabs, 5/16" wide, used to turn a headlamp socket into a plug for interface with existing wiring.
Heat-shrink tubing, 3/16", 1/4", 3/8".
Cable wrap.
Zip ties.
Bracket material, .045" sheet steel.
Stainless screws and hardware, 2.5 mm and 4 mm, for resistor and relays.


1. For H4 lamps, left and right sides are fused separately. If one fuse blows, the high- and low-beam functions still will work on the other side.

2. Not all high beams are on one relay/fuse. This keeps current drain well under rating of wiring and relays, even with high-wattage lamps. I am able to use fuses that blow before the current rating of the relays is reached.

3. The H1 lamps are controlled separately from the H4s, allowing me to add a switch to the dash if I want to disable them manually in the future. Or one set of lamps could be set up to be daytime running lamps, etc. All relays are actually SPDT for future flexibility.

4. Maximum voltage drop with sealed-beam lamps is 0.2V.

5. Implementation details: all wiring is rated at 105 deg. C. All relays are US-made by Tyco (formerly Potter & Brumfield/Siemens, not sure in what order, but both good names). All connections crimped, soldered, and strain-relieved.


1. Added complexity and cost with respect to classic 2-relay/2-fuse approach. 4 fuses and 3 relays.

2. Lots of wire.

3. Connector for passenger side H4 is not accessible from rear without removing relay mounting bracket. Might be able to reach it from the front with lamp out.

4. Implementation details: Tyco relays do not have two output terminals, resulting in extra work to connect two 12-gauge wires to one terminal. Also, headlamp connectors came pre-wired with 18-gauge, and this had to be pulled out for attachment to 12-gauge wire.

Notes from Dan:
1. I found it easy to remove the 18-gauge wire from the headlamp connectors by lightly tapping (emphasis on LIGHTLY!) a small nail into the crimp areas to spread them apart enough to allow the 12-gauge wire to fit. This trick can also be used on the ring terminals as well, to fit more wire into the crimp points. I combined wires in the ground ring terminals so that now I only have two grounds that I need to worry about.
2. For the high beam connectors I cut, then filed off the third "slot" in the connector, just to neaten it up a bit and make it a little less confusing.
3. I cut the bracket out of sheet metal from spare computer cases I had lying around. Works great.
4. One last thing: The bracket is for mounting the relays next to the battery, on the inner fender bolts (you'll be able to match up the holes easily).

LINK -- PDF wiring diagram

Posted April 16, 2003

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