It sounds like you are on the track to find the problem. Voltage testing done by disconnecting parts of the circuit is a good idea for getting an idea where the problem is, but that method can lead you to thinking something is working when it isn’t. To do a proper diagnostic voltage test everything must be connected, and all the pertinent relays installed. Sometimes I’ll hook up test wiring leads to allow me to probe certain points in the circuit with everything connected. I’ve soldered test leads to pins on relays for example. Suggest to re-connect everything, and measure & report the following 6 voltages with the key in “s” and gear selector in park.
- Battery + to battery -
- At the top of the fusinble link to battery -
- At the bottom of the fusible link to battery -
- At the top of the purple wire to battery -
- At the start terminal on the starter motor to starter motor case
- At the start terminal of the starter motor to battery -
You testing reported above, if I understand correctly, suggests there is a bad connection between the starter relay and the s terminal on the starter. Or the starter solenoid coil is shorted out. Be aware this might cause something to heat up as you do the testing above, and melt wire insulation or something. So only turn the key to “start” briefly, just long enough to do one voltage measurement.
At least you know now why it won’t crank. Zero volts on the “s” terminal of the starter.
I’m sympathetic to your volt meter problems. Mine went south on me the other day and got me confused during a voltage measurement. Turned out the wire inside one of the probes had come unsoldered.