Electrical Crank-no start ... no spark ... no injector pulse, was it something I did? (redux)

Have a similar thread posted here - it seems to have burnt itself out.

I have new information since so trying this again.

'87 GT

Crank no-start (no spark or injector pulse):

12V at coil +&- (key in run)
12V at injector + (key in run)
Fuel pump primes (key in run)

At TFI module:

Run power in - 12V
Start signal in - 2.2V (in run), 1.7V (cranking) ... I don't get this
Coil negative - 12V (in run), 9.3V (cranking)
Ignition ground - 12V (in run), 8.8V (cranking)
PIP out - 8.1V (in run), 6.3V (cranking)

The start signal voltages I do not understand - the starter cranks normally
I measure the same thing (2.2V) at the start signal wire going to the solenoid (connector off, measuring at connector (key in run).

The PIP (hall effect sensor) voltage does not switch from 0-10V, it's stuck at around 8V, drops when cranking from starter current draw I assume.

When I bypass the PIP and ground the wire I get spark and injector pulse. So the coil is good, the module is commanding the spark, computer is firing the injectors - when I artificially generate the signal.

Logic would lead you to the PIP being the problem.

Now here's the "by the way",
The car was running very well, I was getting set to put it into winter storage.
Figured I would check timing & idle speed because, why not.
I have a hand-held tach that I wanted to use (it's more accurate and convenient).
I back-probed the coil negative connector to get a signal - it was not working.
Wiggled the wires and connectors a bit, no luck, figured there was a problem with the tach.
Shut car off, disconnect everything ... car won't start and hasn't since.
I have to assume it's something I did but for the life of me I can't remember anything weird happening.
No spark, no flash, no smoke, no smell.

Any ideas?

I hear you about the computer. I've been through most of that crank-no start checklist but as the man says, you have to go through it all, in order. Of course, human nature had me hoping to find an obvious (simple) answer (pickup coil, TFI module etc.)