1995 Mk3 GTi problem.

[JW590]

The Mk3 GTI (remember this thread http://www.golfgtiforum.co.uk/index.php?topic=210978.0) sat on my drive from 16th November until last weekend. I thought I'd better finish it off and get it sold. It started first time. I did all the hard wiring that was necessary and then it wouldn't start. Yesterday I got it started, however this morning.... The following is what's happened - and any help would be greatly appreciated. Here we go....
 
Fuel pump relay feeds fuse 18 with 12v.
 
Pump has a red/yellow wire and a brown wire running to it (I am ignoring the fuel gauge wires).
 
When I picked it up from my mechanics the red/yellow wire had been crimped together, and the temporary 12v wire was running from fuse 18, over the back seats, and spliced into the brown wire.
 
The car worked.... drove home, started it last week.
 
I snipped the brown wire and ran the temporary 12v wire alongside the loom and connected it up properly from fuse 18 to the brown wire at the pump plug (I now realise I had disconnected the earth by snipping the wire).
 
The car would not start.
 
I studied the only wiring diagram I could find http://faculty.ccp.edu/faculty/dreed/Campingart/jettatech/techset/index.htm
 
From this I can see that the brown wire is an earth (indeed it is a short to earth), and the red/yellow is the 12v. I reconnected the brown wire, snipped the red/yellow wire and ran the temporary from fuse 18 to the red/yellow wire on the plug.
 
It worked.
 
This morning the battery was totally flat, not even a display of any sort on the dashboard - so it's been on charge all day.
 
What I've done today to trace the 12v -
 
With everything connected turn the ignition on. After 2 or 3 seconds the (new) fuel pump relay trips. 
 
Take out fuse 18 and the relay doesn't trip.
 
Put fuse 18 back in, take the plug off the fuel pump - therefore isolating it - and the relay still trips.
 
According to the diagram and the (rather disappointing) Haynes manual I have, the only other thing fuse 18 feeds is the Lambda sensor heater.
 
Whilst typing I have realised what I have changed... I need to wire it up so that the temporary 12v is connected to the brown wire - while the brown wire is still connected to the pump and earth. I do not understand why, but rather than blowing the car up the thing will probably run... after all, that's how it was before.

Has anybody any ideas on what the problem may be?

Thank you

John.
 

[danmusic24]

I reckon you've got a wiring problem

[JW590]

Well it's a start.....

[Leon27]

I reckon you've got a wiring problem

Love this forum because of people like you (mean that in the nicest way btw!)

Really wish I could help properly but reading about the car and seeing it are two different things, nevertheless!

Firstly do you think the car drained the battery because of the fuel pump fault or is it from a seperate issue? If it is a drain then disconnecting the relay and F18 might help to diagnose the problem if the amp draw drops.

Mk3 as well as Mk2 fuseboards have been known to cause problems themselves. What's concerning is that by pulling the plug off the pump that the relay trips regardless. I would assume if there was a wiring problem to the pump that the F18 would pop so if the car runs at the moment I'm hoping the wiring is actually ok?

Fuel pump relay feeds fuse 18 with 12v.

The ECU is sending a signal through the yellow and blue wire to activate the FP Relay so when you say its tripping, is the yellow and blue wire loosing its voltage? Probe it and see.

From your mechanics wiring repair about crimping the Red/Yel to the Earth I don't understand that, would be easier to see in person I'd suspect but the earth from the pump seems to go back into the fuse box for whatever reason, then to battery ground, have you done the same or earthed it to ground near the pump? I don't know why VW would do this unless that earth is monitored or something through the fusebox? Or the wiring diagram is dodgy, and it would not be the first time...

To note, I had a misfire fault caused by the alternator which cooked every Relay 30 I put in it. Apparently there was some sort of protection built in the relay which the alternator kept frying to prevent the ECU from being overcharged. If you have a spare working 167 chuck it in and see what happens.

Hope that helps