Could be something to do with the different EU regulations around in the late 80s-early 90s, mostly to do with emissions.

Best thing to do is just keep swapping wires until you get to the correct configuration for the UK OFAB and MAP that you have - it's not that hard to do.

The OFAB wiring diagram is what you need to follow - you should be OK with or without the supressor - but get the supressor to be on the safe side.

Let us all know once it runs!