The wiring diagrams from ALLDATADIY do in fact have the wiring colours, (in tiny little writing), so that was a BIG help. It seems that all my problems were due to the wiring to the MAS shorting out, as it is now running sweet as!

SO I ran a new home made heat shrink covered harness, (it's only four wires), back to where the MAS wiring disappears beneath the brake booster into another very major harness coming from, (or going to?), the fuse box.

On one of these MB forums I saw an example of someone who had cut a plug open to replace the wiring inside and I used that as a model for my repair. I had to use a a razor and a hammer to gently prize open the molded plug. Downside is that the epoxy I used to close it all up isn't hardening very fast, (it's been 24 hours), so I have braced it and hope the heat above the exhaust helps the epoxy to harden otherwise I'll have to come up with plan b...

I can see why they didn't replace the MAS wiring when they did the rest of the engine bay harness, and I can see why MB changed the later MAS wiring to go across the engine bay. I slid heat shrink as far back over the original wires that I connected my new harness to. The wires that far from the engine bay looked like they were in pretty good shape anyway, but I won't be putting any money on them not playing up in years to come...

Regards

Wayne