The electrical relays on my '84S seem to run quite hot - is this normal? Also the voltmeter normally reads 12V, but dips when the turn signal flashes, wipers cycle and when lights and AC are on. Is this normal or is there a grounding problem? Alternator is rebuilt with new voltage regulator and output appears to be fine. Battery is new. TIA for any help!
It certainly sounds like you have ground issues if the voltage dips - very common in 928s and one of the first things that need attention. Bad grounds result in many faults and are easy to remedy. This is generally one of the first tasks for a new hands-on owner to tackle. It is also not uncommon for mechanics not familiar with 928s to prescribe a new alternator which has little benefit - that was true for my car before I acquired it.
There are diagrams available to point out where all the grounds are. Each one should be unbolted, cleaned and all of the attached terminals cleaned (generally by mild abrasion with something like a Dremel with brass brush and/or chemically an electrical contact cleaner) and then the grounds re-bolted. There various treatments that some people favour to improve electrical contact and/or resist corrosion.
Hot relays can mean bad relay contacts - again cleaning contacts is an 'early job'. The central electrical panel (CE) is in a position that it be hit by water leaks from interior fan, sunroof and door/window, so corrosion on the relay and fuse contacts is common.