I had a stock temp gauge that was reading too hot which was not accurate. I had another gauge cluster and thought I would change out the temp gauge to see if it might work better. The gauge was bad and caused a short and blew a fuse. I put the old temp guage back in the cluster. Now I have no gauges working.....Did I screw up the voltage regulator mounted on the back of the gauge cluster?
Been there done that! Mine was a gas gauge in a 67 Mustang that I replaced, like you, with a another gauge from a spare cluster. Put every thing back together only to discover that now none of the gauges worked. Found that I had blew the 5 volt voltage regulator. Replace the regulator, with the one on the spare cluster, same thing, blew that too. Like a dummy I went out bought a new regulator same story! I had now gone through three voltage regulators and still had dead cluster. What I eventfully discovered was that my replacement gauge was shorted to ground through the mounting screws. I remounted the gauge and checked with an ohm meter and that fixed the problem. Also, I replaced the mechanical regulator with a solid state one from Radio Shack part # LM7805. I think the mechanical regulator was around 30 dollars and the solid state one was like a $1.20.
Your circumstances may be different as I believe the 70 Mustang cluster is mounted on a printed circuited board where as the 67 was hard wired. But for what it's worth that's what happen to me. Good tech articles on the subject:
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