Did the tacho originally work correctly in the coupe?
And when you wired it up and the engine wouldnt run, how exactly was it wired?

Thanks to phunkdoktaspok's wisdom. I realised that the tach can go either side. please ignore my previous posts. If the diagram is from the factory wiring diagram then follow that.

Dude its all good mate, I am sure others were thinking along the same lines. Thanks to yourself it has just been brought out and hopefully its been clarified a bit clearer for everyone.

phunkdoktaspok, I'm not sure if the tacho worked in the coupe as it has no engine.
When the engine wouldnt start one end of the looped wire (b/w) was into the ignition barrel as shown in the posted wiring diagram, and the other was on the negative side of the coil.

So if it was only looped and there was no physical connection made to the tacho, you couldnt have burnt the tacho out. Having said that, you still don't know if the tacho is actually any good from the start.
The only thing I can think of, and its highly unlikely, If you connected the loop wires back to front ( the loop has to run in a certain direction and power has to flow through it correctly) If it is wired backward the tacho will try to work backward ( ie, it will try to go from 0rpm to -0rpm, if it is this, what you could be seeing as reading correctly, is the needle bouncing off the 0 rpm stop. ( like I said its highly unlikely)
But you can still check it out anyway.
When wired up correctly there isnt anything realy besides a fauly gauge that could cause this.

Thanks doktaspok, I'll try switching the wires tomorrow, i didn't think the direction was of much importance, so i didnt try both ways.
I'll post how it turns out.

It Worked!
switching the signal wires was all it took, thanks for all the help

Good stuff.
I didnt think it would fix it as I have wired then backwards before and they never reacted like that.
But its good to see everything worked out for you.
Cheers Steve

is it possible that if wired incorectly (should read incompetantly) that it could stuff my coil, i dunno what i did, any suggestions??

If you dont know what you did, how can anyone answer your question?
The only way you could stuff a coil through the wiring is;
put to much voltage into it,
or put power and earth to it and let it sit and get hot till it either melts or explodes