The schematic shows that there is a note for switches 1-8. However there is nothing further there. I'll have a look at my machine and post what I find.
The schematic is missing something 
No stress....I appreciate your help!
The red has been cut in the backbox. The yellow is definately hacked into the red. The other end of red is under PF...I've gone over it and the yellow is definately in the place of GRN-RED.
The naughty wire at PIN1 (GRN-??). I've traced it back, managed to cut myself in the process, is one which goes back to plumb, coins, credit, slam and trigger....
I think you are right re the plug...Maybe when its been soldered (pin 1 & 2) as they have melted plastic when under load they are shorting between the two??? I ran the buzz from one, and it didn't pick up the other but just a thought - apart from the hacks.... I am happy to remove the yellow, but I suspect its been done for a reason as the GRN-RED may have been pinched somewhere....
Anyhoo. Enough for tonight...Need to glue my finger back on and spend a little time with the boss....
I can't find the replacement plug on Marks site either...Have they a special name?
Thanks
