78 Spider was fine until wire(s) crossed & alternator/starter wire(1 wire between them) almost fried in places & fuse blew (altern fuse) No idea what happened. I put new wire between altern & starter and wire is hot (12V) at altern at all times & starter also. Fuse is not blowing now & voltage reg. seems OK.
Tried ignition switch & no starter at all, no clicking or other. Crosse solenoid & starter posts & sparks (no solenoid activity) I may have burned up solenoid when wires were crossed?
AND check starter wire @ ignition & when ON, red starter wire remains HOT. What gives? Is ignition switch fried or solenoid? OR both?
Some solid advice would be helpful.

First disconnect the alternator. It's possible for a rectifier diode to be damaged enough to feed back without bowing the fuse.

Then all you can do is go though the relays and fuses-one by-one.

I would not trust the Vreg diode either. At least fit a voltmeter so if it does fail you want fry the battery. I fried one on a motorbike by doing some arc welding work. I disconnected the battery but had not unplugged the alternator or the ECU. The ECU was thankfully OK but a month or so later, I had a flat battery that had been cooked by the alternator going over voltage.

Thanks for the input. My next step was to isolate the Alternator wire from the starter as yo just mentioned. I am trying to find out why both starter and alternator are getting voltage even with no switch on. Seems odd.

Are you talking about the fat wires or the skinny wires? There’s a fat wire on the alternator and an even fatter one on the starter. They both go directly to the battery(more or less), so just switching them should not have caused an issue. If you tried to start it like that, of course then you’d have an issue. The skinny ones are a different story. You also said you put a new wire between the alternator and starter. There is no wire between the 2. Did I misunderstand? What wire(s) did you replace?

An alternator will always back feed when the rectifier fails.

It's easy to test use an ammeter between connectors. On a bad example you might see a system volts drop when the alternator is connected.

Wiring diagram shows conductors between solenoid and alternator and that is wire that fried for some reason. I replaced it. The high voltage may have toasted my solenoid, I am not sure. I am back to square one and will test solenoid more to verify good or bad.
thanks for reply.

According to the diagram I have, there is a black wire that goes between the starter solenoid and the alternator. Is that the one you’re taking about?