Loopback Plug

[Steveh24]

I have a wire loom coming out of my VW TDI 150-5 engine that has a plug with a couple of loopback wires connected to the end of this wire loom, if the plug is connected then everything is fine, if it is taken off then the engine is very rough and vibrates a lot and if you push the throttle forward the engine revs will not increase the gearbox will not engage.

Does anyone know what this little plug is

 

[flappy]

Leave it alone..

 

[Steveh24]

 

[glandyman]

@GPSguru might know Steve.