As you did not identify to the contrary, I am going to assume you tried to plug in a SSS dash cluster into a standard P510 wiring loom for the first time and the gauges did not work?
Not sure if you know, the pinout on the round cluster plug and other wiring is different between the SSS and the standard (not SSS) dash cluster......
Therefore, before you go too deep into trying to ID and / or fix the voltage regulator, are you sure you have all the pinouts correct for the SSS Dash compared to the STANDARD P510 wiring?
While I normally don't like to cross reference different forums, however in order to correctly reference the information and credit it's author, this post from the510realm covers this wiring difference and saves having to trace each wire from the factory wiring diagrams; it worked for me.....the top schematic is the "non SSS" and the lower schematic is obviously the SSS one.
http://www.the510realm.com/viewtopic.ph ... 24#p268018
Let us know how it goes....good luck!