Do your headlights seem dim when driving around at night? Would you like to have a huge improvement in your nighttime vision? If so, this article will describe how to upgrade your wiring, and optionally, to convert your headlamps with H4 conversion lamps!


As you are probably well aware, the headlamp wiring that comes stock on many of the early 80's to mid 90's cars is of a very small gauge and full of points of resistance. For example, on the '84-'89 Daytonas, the power for the headlamps follows a very long path; it comes from the battery to the headlight switch, through the steering column dimmer switch, then through a wire that splits into two and goes all the way around the engine compartment finally reaching the headlamps. Obviously this is not the optimal setup, so the following article will show you how to upgrade you wiring for more voltage. In my car, this procedure increased the voltage from 11 volts (a 3.2V loss!) to 14.1 volts (only .1V loss!). While 3.1 volts may not seem like a lot, headlamp output decreases exponentially with lower voltage, so it makes an immense improvement when driving at night.

Parts Required

1. 2 Bosch Style Relays

2. 12 or 14 gauge wire for the lamps (Multiple Colors)

3. 18 gauge wire for the relay control wires

4. 2 Inline fuse holders

5. 2 H4 Conversion Headlamps (Optional, but highly recommended)

6. Soldering Iron and solder

7. Wire cutters-strippers…


This is a schematic of what the completed circuit should look like when it is finished. Refer to the instructions below for more details and pictures.


1. The first step in this project is to determine if you are going to use the original headlamps or if you are going to upgrade to a H4 conversion headlamp. The H4 is much more efficient than a sealed beam lamp and therefore will produce a much brighter beam on the road. The lamps I recommend are the “Free Form 165mm Hella H4 Conversion Lamp” These are a cross between American DOT and European E-Code lamps, and are still DOT approved.

2. Start by unhooking the battery and removing any induction tubes, etc. that might get in the way of the wiring behind the battery. At this stage you should also scope out a location to run the new wire from the Drivers side to the Passengers side. I chose to run mine under the radiator core support.

Picture showing the new wire 


2a. On the ‘87 Daytona I was doing this conversion, I noticed that there was a loop of two wires behind each headlamp, one for the high beam and one for the low beam. There was also a diode in each wire that was causing a lot of the voltage drop. These loops of wire were easily removed and bypassed because they were connected with a 4 prong connector on each side. I chose to do all of the wire splicing here because the wiring after this point was in good shape and it made the installation easier. If your car does not have these plugs, you will have to find another place in the wire to do the splicing.


This is a picture of the diode once it was removed from the car


3. Now it is time to start wiring the relays. Start by cutting the original wire that went to the low beam headlamp on the drivers side and extend it using the 18 gauge wire, run this to the location of your two new relays. I put my relays on the fender next to the ASD relay. Now connect it to the “85″ terminal of the relay that you want to use for the low beam. Next cut the high beam wire and do the same thing, but running the wire to the new high beam relay.

4. To ground the new relays, simply run a piece of 18 gauge wire to each “86″ Terminal, and connect them to a new, CLEAN, chassis ground.

5. Now it is time to start working on the high amperage side of the circuit. Start by running two 12 gauge wires from the battery to their own individual fuse holder. Then run one fuse holder wire to the low beam relay (Terminal “30″), and the other wire to the high beam relay terminal. Because I wanted the fuses to serve as protection from a dead short only, I put a 15 amp fuse for the lows, and a 20 amp fuse for the highs.

6. Now run the output wires from the relays to the headlamps. Run two 12 or 14 gauge wires from the “87″ Terminal of the low beam relay to the low beam terminal of the headlamp. I found it useful to run a single wire from each relay, and then make the splice further down the wire. Do the same thing for the high beams.

7. Now it is time to tidy up your work. Remember, you are relying on these wires to let you see at night, so tie them up away from moving parts and make sure that they will not get cut. I ended up taking the whole harness out and wrapping it up in electrical tape to make it look stock.

Picture of completed wiring harness 


Pictures of the relays in the car (the relay closest to the strut tower is a secondary radiator fan relay)


8. The last step is to check the grounds from the headlamp to the chassis. The drivers side ground goes to a screw behind the battery, and the passenger ground goes to a screw that is on the frame near the alternator. The stock 18 gauge ground wires were shot in my case and needed to be completely replaced. I replaced them with 14 gauge wire, and made new ground points while I was at it.

9. Turn on your headlamps, make sure the high and low beam work, and enjoy your new found brightness!

Photo of the Hella Free Form Headlamp