I'm finally going to install my boost gauge but am a bit stuck on the wiring for the light. I'm going to power it off of the headlight switch. I have a red and black wire coming from the bulb on the gauge, which wires should I splice them into on the back of the light switch? Is the black an earth?

the red and black wire off the headlight switch is ignition live and brown will be the earth, i imagine the red off your gauge will be live and black the earth. hope thats helps

This is what I used when I powered my w8 mod (I wanted non-dimmed +12v when either side- or head-lights were on):

so live to one and earth to the other? What numbers live and what's earth .

Cheers mate

By the look of the heatshrink on the cable I would have to say:

10 = ground

14 = +12vdc (pre-dimmer for instrumentation)

I just solder straight onto the pins on the plug using a small soldering iron and a steady hand.

If you want to be really good, you could put a fuse inline too.

I'll just hold the wires on the connections, turn the lights on and see what happens if its okay then I will tap into them.

So number 14 is live when the lights are on :yes:

I'll just hold the wires on the connections, turn the lights on and see what happens if its okay then I will tap into them.

So number 14 is live when the lights are on :yes:

Indeed, better still use a multimeter

will do

How can I check the earth with a multimeter? Could I put one prong on the cable and the other on a known earthing point and see if I get a "Beep"??? If I do then that cable is an earth?

That would work, better to use a proper resistance setting rather than just the beep. 10-body/earth point should have minimal resistance.

To then check the 2 pins, as confirmation stick the probes on 10 and 14, and the meter on v-dc. With the light switch off you should see zero, and with the lights on somewhere between 12 and 14.

How can I check the earth with a multimeter? Could I put one prong on the cable and the other on a known earthing point and see if I get a "Beep"??? If I do then that cable is an earth?

Do you have a test light? You could put the wire to earth (ie the door hinge) and the prong to the positive to see if it lights up, or do the same with a multi meter.

Make sure the surface is unpainted as well.

Edited 7 June, 201115 yr by urbanfox

Could I use the test light and hold it on pins 12 and 14, if it lights then it's okay to use?

Could I use the test light and hold it on pins 12 and 14, if it lights then it's okay to use?

Dunno what pin 12 is used for without consulting my wiring diagram, but 10 & 14 should cause a test lamp to light.

Sorry I meant 10 not 12

The wires are right mate cheers. I've hooked up the gauge and will solder the wires in place tomorrow. I don't know why I bothered with the boost gauge as they aren't really necessary, but I had one lying around.

Excellent job :-) I really should get on and fix my W8 mod after the windscreen man cut through my cable :-(

The wires are right mate cheers. I've hooked up the gauge and will solder the wires in place tomorrow. I don't know why I bothered with the boost gauge as they aren't really necessary, but I had one lying around.

I find them usefull for identifying any issues with the turbo or problems like a VAC leak

I find them usefull for identifying any issues with the turbo or problems like a VAC leak

I wondered about fitting one to my TDI to see what it is was up to..... but I did not really want to pay lots of money for one....

There is an earth point under the A pillar cover that I used.

Only have to tap into 1 wire then

There is an earth point under the A pillar cover that I used.

Only have to tap into 1 wire then

oo can u put pic up??

I ended up redoing the wiring and now run it from the glove box light :yes: