Sorry to ask again, but I can't read electrical wiring diagrams.
It's only a figure. You only needed to look at the connectors output pinouts and figure out the voltages that are being supplied. There's no electronic knowledge needed here. Lazy, eh ?

I've installed the Hantarex MTC 9000 monitor in the Atari DL cab and also in installed a Hanterax Us250 psu and taken out the Atari original.....
As I already said in one of my previous messages, there was no need to do such a thing to install a MTC-9000. Oh well...
Now my new problem, on the psu it has a neon lamp out, I connected it to the original atari lamp, it came on, with a very loud hum then went off.
I don't know what neon lamp output you're talking about, but anyway, did you measure the voltage coming out of it before attempting to connect the original Atari neon light wiring harness to it ?
The original neon light ran on 115 V AC (as per manual, that you probably didn't read) and I strongly suspect that you supplied 220 V AC -> you toasted the neon ballast
Matteo