[L Sjoberg]

83 SC, bone stock save for MSD coil. circa 169k miles. rebuilt Bosch alt, new coil, new battery, etc., after the alt died while driving. have cleaned all grounds, as well. now the question:

intermittent no tach - sometimes tach will start and stay dead, other times will fire up at about 1500 rpm and then slowly fade to zero while driving, other times will function normally. also intermittent speedo - sometimes dead, sometimes will kick in only above 20mph, other times functions normally. also intermittent dead ignition, i.e. key will turn all the way right but no triggering of a start operation. otherwise, car runs perfectly normal.

curious if there could be any root cause of an almost-certainly dying ignition switch? it's always possible of course that the fried alt also killed the tach and speedo, and of course all kinds of things can go wrong with a 40 year old car (especially since I know the quality of the mechanic, namely me).

apologies if a stupid question, even ancient electrical systems are often Greek to me, regardless of how many diagrams I try to read. trying to assess any potential for commonality, before I start tearing about things individually.