My OEM style reproduction tach goes up in smoke

[smorg007]

Hi gang,

I reached out for help on this forum to prevent this costly mistake, what went wrong. I installed an OEM reproduction tach in my truck. The only difference is my truck has been upgraded to mid 70's HEI distributor. On the supplied Brn/Pink wiring harness I swapped out the round connector for a female spade connector and hooked the brown wire up to the male spade terminal on the HEI Coil labeled "TACH" instead of the "-" side of the stock coil. I then connected the pink wire inside to the fuse box to the "IGN UNFUSED" connector. Connected the other end "V-shaped" connector to back of tach and started the engine. Tach worked perfectly. (Even close to accurate) I drove truck back to my home about 2 miles away and everything was good to go. Have not driven the truck until yesterday. Pulled it out of the garage and let it warm up, tach working just fine. Approximately 10 minutes went by and I drove towards town but only made it another 2 miles when I smelled something burning. I looked down at my tach and noticed the glass face over the tach was full of smoke and the tach was reading "0" and stopped functioning. I pulled over immediately and unplugged the pink wire from the fuse block. "WHAT WENT WRONG"
I searched the threads and read these http://67-72chevytrucks.com/vboard/s...archid=2110180 that indicate everything is compatible with HEI. Another tach gauge is $100+ and I do not want the same results.

What can I do to determine what went wrong and what to do to prevent this from reoccurring again. I'm hoping my lesson can be used from another member ending up with my tach up in smoke results. I spent the money on the upgrade conversion to enhance the looks to my show truck.