Headlight wiring upgrade

The Mad Hat Man

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LZIR Despatch Agent
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Found this on another forum - hope it helps. It might well resolve the molten headlight plug problem and, because the headlight power is straight from the battery, will ensure maximum power goes to the lights.



the wiring diagram above is for a generic headlight wiring loom up grade and will work for both positive and negative switched headlight systems.

If the new loom is made to the diagrams set up and connections made to the vehicles existing headlight sockets, then there will be no need to cut into or alter the vehicles wiring in any way.

Once the new loom is installed, the vehicles headlight globes will now be positive switch no matter what polarity the vehicles headlight switch work by.

The reason for using 4 single pole relays instead of 2 double poled headlight relay is to increase safety. If standard double poled headlight relays are used and a fuse blows or a relay fails, you can loose either both low beam or both high beam at the same time.
By using 4 single pole relays, if a fuse blows, you will only loose 1 high beam AND 1 low beam, or if a relay fails you will only loose either 1 high beam OR 1 low beam.
This is a much safer way to operate the headlights.

The 4mm2 Automative wire is way above what is needed but by using the heavier cable, and by running an earth wire from the headlight bulb all the way to the battery, the standard headlights should be brighter and slightly whiter.

With this set up, the relays are protected by the vehicle’s existing headlight fuse but the current that is required to operate the headlights via the vehicle’s headlight switch is now about 1/50th of what was needed before the new loom was installed and this should considerably extend the operating life of the vehicles headlight switch.

Parts required..
4mm wire
2mm wire
Fuse box (or Fused Relay sockets such as VWP RS3F)


15A fuses
4 relays
4 relay bases. (or a 4way relay socket such as VWP RB4U)


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The way i read it - the original wiring is so convoluted that you are likely to get a voltage drop at the headlights, resulting in dim lights. A known 200TDi problem. So this circuit uses the shortest, most direct route for the headlight power and only uses the old circuit to operate the relays - a much less voltage critical circuit. It also has the advantage that spot light feed can be also taken from the headlight side of the relays, if they are rated sufficiently.
I will have to look into this as my flash doesn't work but my high beam does and when my lights are on it seems to drag alot of power from the alternator so would this help my power drain with the lights?
ah so to sort my flash problem I need a new stalk then get stuck into wiring in these relays.
excellent cheers for the help
what causes the stalk contacts to burn out is it upgrading bulbs if so standard holagen bulbs should not cause a problem..?.?
Resistance due to bad contacts burns out the stalk, resistance creates heat. Like any electrical switch they need cleaning, you can disassemble them to clean , they are very basic, or run a can of servisol through them. When clean the switches are more than capable of handling the power. An easy mod to do to the wiring is to run an earth fly lead from the lamps to the battery, 9 times out of 10 the problem lies at the earth side.

Without maintenance the electrical system will deteriorate , then matey thinks he needs brighter bulbs , brighter bulbs pull more amps, more heat is created , the system becomes a hazard. Ive seen fuse boxes getting so hot the plastic around the fuse melts, so if you have glass fuses make sure the contacts are clean and bright.