mallory 11k tach hook up w/points dist. help please !

It is a used tach . do not know history on it .......
Yes tony ........ I took the cover off and looked inside and there was a switvh for 4,6 or v-8 engines . It was on the 8 number for v-8.
All the wires were intach , nothing cut or pinched.
don't know if it was a tach for a pos. ground.

I hooked it up to my other dart with a msd unit and a electronic dist. the needle would idle right for a few seconds then start climbing without even reving the engine..
then the next time I touch the red wire to the battery pos is sparked all over. think it is shorted out inside..
I think the tach is junk..
oh well ...... I tried.