1977 Tachometer into a 1990 Cluster

Well I put the 77's gas where the battery idiot light used to be. I put the tach where the big gas gauge used to be. I hooked it all up and everything worked for a few days. Then the tach started randomly
jumping around and finally just stopped around 4K. I checked all the wiring and it seems to be correct - ground, 12V, and Hz at the coil wire. These gauges were a little nasty out of the 77 so I re-painted them, the gauge may have been on it's way out no way to know.... I can't get the gauge to do a thing so either I fried it or it just died? Thanks for any input....
GMC Gremlin
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.