In Search of Mothra - The Crucial Headlight Upgrade

Just upgraded the 73 3.0 CS with Cibie H4 80/100W outer headlights and H1 100W inners. The difference is dramatic and after getting them aimed at the dealer have had no problems with other drivers thinking my brights were on. This upgrade will comfortably handle the required current loads with a bit more than a 2x safety margin based on a chart at The existing ground wires are adequate.

My stock alternator has a 55 amp output which is adequate when you consider other things that may be running simultaneously like cooling fan, A/C, high output stereo, and horn (to confuse Mothra when she finally arrives). Forty-five amps is probably not adequate if you'll be using the brights for any extended period so it's worth checking it out to make sure. There's a sticker on the alternator that indicates the output (if it's still readable).

Total cost will be around $350. The headlights with the bulbs pre loaded came from PLR Group for $252 plus about $12 shipping (770-271-1100). This is a special price (normally $370) that Jackson at PLR will continue to honor if you mention this article. Aiming the lights was $45 and the rest is for parts and any tools you may need as follows: (NAPA Auto Parts or Radio Shack where indicated)

Remove the front grills and headlights and then the headlight holder frames. Watch for washers between the frames and their mounting tabs that may have been used to fine tune the position of the frame relative to the grills. The new H4 outer beams have a 4W city light with tabs extending down requiring you to notch the headlight aiming bucket. If you look at the frame, you'll see a precut notch at 6 o'clock. Make the notch in the bucket to match. It looked like a pain to remove the buckets from the frame and I was glad I didn't have to. I did not connect the city lights but if you do, wire them into the parking lights on the sides using those blue tap splicers.

Find where the ground wires are screwed in at the sides and remove the screws. Scrape away rust around the hole and from the terminal end and replace the screw with a new one if it's rusty. This could make a big difference. Trust me on this one.

Hook up the 12ga white wires to the inner and outer beam plugs. Cut two pieces of white 12ga wire: one 3' for the left and one 7' for the right. On each wire, strip about 1/2" from one end and another 1/2" from the middle of the wire a distance back somewhat greater than the distance between the inner and outer bulbs. At the inner beam there is a single wht/violet wire. At the outer beam, a double wht/violet wire coming from the top position of the outer beam plug. Cut them all about 2" up and strip about 1" off each wire. Wrap the wht/violet wires coming from the plugs around the stripped portions of the 12ga wire, solder, and slide over a piece of heat shrink tubing or wrap well with electrical tape.

Remove the battery. Attach the 12ga wires along the harness using the zip ties and feed the ends into the engine compartment through the hole where the harness passes on the left. This can be tough. I bent wire from a coat hanger in half, fed the bent end through from the inside, attached the 12ga wires with wire and duct tape, and pulled the whole works back through.

Turn the existing high beam relay into a low beam relay. Remove the horn and high beam relays and slide the holders off. Separate the wrapping tape to expose the wires in the harness about 5" back from where it leaves the engine compartment. Find the thick (2.5mm^2) yellow wire, slide one of the small screw drivers between it and the rest and cut it. Find it again where the wires go up to the relays and pull it out. Do the same right where it exits the engine compartment. Attach a snap-on female terminal to the yellow wire by the relays. Using the tiny screw drivers, remove terminal 86 with the two white wires from the high beam relay and replace them with the yellow wire. From the load shedding Bav relay, remove the terminal with the red wire and put it in slot 87 of the high beam relay after removing the terminal with the two wht/violet wires. Clip those wht/violet wires; they're no longer needed and won't carry any current. Terminals 85 and 30 are OK. Insert a 15 amp fuse between the ends of the yellow and red wires and your low beam relay is complete. It will go empty slot where the fog lamp relay would go. I put all my fuses between the hood strut pivot and the front engine compartment wall. If you changed some the wire lengths, they could also go beneath the headlight access panel. Dealer's choice.

Wire up the new high current high beam relay. First, enlarge the middle slot as indicated above. Touch up the bare edges with your favorite rust inhibitor. Two 1' pieces of 12ga wire need to go to terminal 87. I spliced mine close up on the existing wires with a solder joint and heat shrink since I couldn't make one of the snap-on female terminal ends work. Remove terminal 86 (green) from the load shedding relay and insert the terminal with the two white wires you removed from terminal 86 of the now low beam relay. Make a lead from the 10ga red wire to from the alternator to term 30. Leave term 85 and tap splice it's brown wire into one of the two adjacent brown wires coming from your new low beam relay. Install 20 amp fuses between the two 12ga white wires coming from the headlights and those coming from the relay. Your new high beam relay is complete.

Make sure there will be no chafing on any of your wires. Enjoy and happy moth hunting.

Thanks to Bill Bremer for his good advice. The 10/98 Roundel article by Mike Miller is also a good reference.

Jim Ockner