Relay issue.

[T4TT]

Morning chaps

I have got a VW T4 Transporter running a Audi 1.8T 20v engine and MS1 V3. Using the wiring diagram I had everything working fine, van through mot etc...

The issue I have is there was an electrical issue where a wire got knocked off the back of the fuse board, that was re-connected and during fault finding the relays replaced. Both relays I have used are the same four pin with same numbers on as diagram. However now the wire from the ecu to the relay is only putting our 4.7Volts and its not kicking the relay over so I don't get power to my fuel pump, etc...Should this wire put out 12Volts?? I have put a 12v wire to the same pin and you hear it click but this doesn't work for the megasquirt wire. I have looked at the solder joint which seems secure and there doesn't appear to be any breaks in the wire. I have tried the relay i had a originally and it makes no difference. For now i have just bypassed the relay but rather have it hooked up properly.

Any ideas?

[DaveEFI]

The fuel pump driver circuit on a V3 board supplies a ground. So the other side of the relay coil has to be connected to +12v. Relays very rarely fail. If you have shorted the pump driver, it may well have blown the output transistor.

[T4TT]

Ah well i think it was putting out 4.7v so must be bad? Is it a transistor i can just desolder and pick up from maplins? I didn't build the board but can solder just never solder a circuit board before other than repairing dry joints. Any idea which transistor I need to check diagram would be awesome!

[DaveEFI]

You'll find the schematic for the pump driver circuit in the manual linked to from the top of this page. Since you've got an MS1 V3, make sure its the one for the V3 board, as the earlier V2.2 uses a different pump driver.