Headlight loom uprating
From THE Corrado Forum Knowledge Base
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Up-rating the headlight wiring loom on VW Corrado
Why do this?
The headlamps lose approximately 2 volts between the battery and the bulbs. The rather long route the loom takes before it gets to the bulbs and the lack of relays causes this. When I fitted this loom to my Corrado the voltage at the headlights dropped by only 0.1 volts thus allowing the full voltage from the battery to get to the headlights. The results were even more impressive when I added a pair of Philips Vision Plus H4 headlight bulbs & a pair of Xenon H3 spot light bulbs (Phillips & Osram bulbs came joint 1st followed by Ring bulbs in a recent Auto Express test).
You can up-rate just the dipped beam as because spots are fitted main beam is usually OK. To wire up the main & spotlights you do the same as for the dipped beam only this time you cut the wire that has 12 volts when main beam is on, this was the White & Black wire on my Corrado.
These guidelines are for a wiring a Corrado and only covers uprating the dipped-beam, but could be converted to fit other VW’s that have this problem.
What do I need?
- As a rough guide you will need the following: -
- A Relay with 30-amp switching capacity
- Quality fuse holder
- 20-amp fuse
- Blade connectors, both the blue & yellow type for the relays & fuse holders
- Ring connectors to connect to the battery
- Enough 20-amp cable to run from the relay to both headlights and run from the relay to the battery.
- Some light duty cable to run from the headlight to the relay and from the relay to the earth on the battery.
- Cable ties
- Insulation Tape
- Heat shrink for the soldered connections (or use insulation tape)
All of the above should be good quality and should be fitted to a high standard as otherwise you may find the lights failing on a dark & wet country lane! If you have any doubt about fitting this you should take your car to a competent Automobile Electrician and have them do this for you.
Instructions
If your car has dim dip i.e. if when the sidelights are on and the engine is running the headlights glow dimly. You will need to disable this. On my car this was two yellow wires that came from a coil that was fitted on the chassis between the NS headlight and battery and was about 10cms long, this had a white plug, simply unplug this. If you don’t disconnect the dim dip coil the headlights will light (not dimmed) when the sidelights are on. N.B. You don’t need dim dip to pass your MOT.
In front of the battery and behind the headlight you will see the loom that goes to the headlight bulb. Switch on the ignition and put the headlights on (not main beam) now using a test light or multimeter identify the wire that is now showing 12 volts, now turn off the lights and check that the 12 volts no longer registers. Now repeat this for the other headlight. This wire was Yellow & Black on my car but may not be the same on all Corrado’s. (Before proceeding further it is wise to disconnect the battery) You should now cut these wires leaving enough room so that you can connect to either end of the cut wires.
I removed both headlamps & the grill as this gave the best access. Headlamps are held in place by 3 screws, the instructions to remove headlamps are in the owners manual. The grill is held in place by 3 plastic tabs.
The first wire that you cut that comes from the bulb side should be soldered & insulated to the 20-amp wire to the terminal 87 on the relay. I fitted my relays by cable tying them to the main battery cable. You will need to connect another wire to terminal 87, this should then be routed to the other headlight, I ran mine behind the grill and connected with cable ties. This wire should then be soldered and insulated to the cut wire on the bulb side. The other end of wire that you have cut should then be taped back into the loom with insulation tape.
Now the wire that you cut first that does NOT come from the bulb but the other cut end should be connected to the thinner wire and then connected to terminal 86 on the relay.
Terminal 85 then needs to be connected to a good earth, I used the negative terminal on the battery.
Terminal 30 should be connected via a 20-amp fuse to the positive terminal of the battery, I would suggest using a ring terminal, as this will give the best connection.
Wiring colours
- Yellow = dip beam
- White = Main beam
- Grey/red = sidelight
- Brown = earth
Reconnect the battery
Your dipped beam should now be far better. If you measured the voltage before fitting the loom, measure it again as you should see a good improvement in voltage at the headlights.
WARNING. These guidelines are for fitting standard wattage bulbs only, if higher than 55/60 watt bulbs are to be used then the wiring, fuses and amount of relays will need to be up-rated accordingly.
Buying a pre-made loom
There are various people on the Corrado Forum that make looms, and you can usually find them on ebay as well. Just make sure you check that it is for a Corrado and it looks like it's of decent quality before you buy it!
Bulbs and wattage
This information is courtesy of Gavin (H100VW)
For information, a 20A blade fuse is happy running 20 Amps continuously. It will blow at 40Amps, double the rating.
Jumping to 80/100W bulbs from std 55/60Ws takes the current in the main beam feed over the edge.
Std main beam in the loom draws 2 X 60W + 2 X 55W total 230Ws dividing by 12V gets you to 19.16A. Going to 80/100W headlights with std spots draws, 2 X 100 + 2 X 55W = 310W dividing by 12V gets 26A.
As the relay intially makes, the sudden increase in current in the wire may exceed the 20A blow of 40A. Fitting the 30A prevents this yet still provides the protection that the loom and relays need.
I don't recommend changing the spotlight bulbs for 100 watters, with 80/100W headlights you will take it over the limits of both the relay (40A) and the cable that I use.
I hope that is clear enough. If not ask again.