Before you upgrade to H4 headlights, make sure your wiring is up to the task.
My 1974 Porsche 911 factory wiring was over taxed and burned, so I replaced several damaged wires and while I was there I added a new 12Ga wire to carry the heavier load. Stock Porsche wires are 16 Ga and are too weak for the common H4 European headlights in my opinion.
Stock USA sealed beam headlights are 35/50W, but newer H4 bulbs can pull 80/130W.
Everyone wants brighter high performance headlights for their sports car, but don’t burn up your stock wiring harness or worse…
The other thing to consider is the electrical stress on your factory headlight switch and indicator switch. My Porsche was designed to route all the headlight current through dash headlight dimmer switch. This extra wire length and various connections lead to substantial voltage drop and eminent failure of the switches.
The solution is to use 30 amp relays so the current bypasses the switches all together. How the new relays are wired and placed in the car can make a big difference.
Some relay kits bypass the switches, but still rely on the old and undersized factory wire harness. My solution still uses the factory headlight wires, but only a small signal current runs through them and the new 12Ga wires carry the heavy current right from the battery.
Below is the wiring diagram that I used to improve my car’s headlight system. I achieved far less voltage drop and thanks to the new wiring and relay, my car can run 150W bulbs!
If you are going to install the relay kit that mounts near the fuse panel or is incorporated into the fuse panel, please check the health of the factory wire harness first. These relay kits can’t undo damage lurking within your factory wire harness.
Watch this video below to see more details on this important upgrade: