Usually if you have to tap on something to work odds are it's a bad ground.

Sure sounds to me like ignition switch related although interestingly my 73 wouldn't start the other day after getting gas and I think the problem was at the start relay. Tapped it and wiggled the + lead on it and everything was fine. No problems since. Started many times with no problems in the 3 months I've owned it. I am a little suspicious of the + connection because I was taking it off to use a remote starter switch to bump the motor when checking timing belt alignment.

I was also going to suggest troubleshootin g using a test light can sometimes be easier than a voltmeter.

Make sure you get one for 12 Volt circuits.

The bulb should be incandescent, (has a filament), which has the added advantage over a Voltmeter of verifying circuit contacts are conducting current. It is possible to measure voltage in a circuit but have no or too little current particularly where switch or relay contacts are involved although this is more common in low power circuits.

 Theres really no advantage of a test light over a dvom if you can use it at all correctly. I worked on cb radios tvs vcrs 150-watt per channel high end audio equipment, have some engineering studies and hobby experience fabricating pc boards designing and building analog and digital circuits.

 A Pinto electrical system is a piece of cake for me. Get those three or four readings I mentioned and go from there. A circuit is a circle so we have to follow it around thats all no jumping ll over the place. Lets get this Pinto going already.

Yes, way too much fish flopping around here, the trouble should've been found in five minutes....... ...........not   like a PCM car with elevendyfortyt wo other things to check.

Once a solenoid has vaporized some of its' internal contact point, it can occasionally not work at one application then go back to working fine. Pull it apart and find the contacts all eroded and pitted to make semi-contact.

Yes, way too much fish flopping around here, the trouble should've been found in five minutes....... ...........

very well would be if any of us were on the scene but that cant happen in the interweb world ..the most simple of things can stump the unfamiliar ....(

Was this issue ever solved?

Geeeezzzzz.... ...it's a freakin' Pinto for crying out loud! If your "mechanic" (I use that term loosely) can't diag a simple issue like this, you need a new mechanic. It starts with a remote start switch hooked to the solenoid, correct? That eliminates everything except getting 12v to the S terminal from.....the ignition switch! Put your voltmeter on the S terminal (with the wire still attached) turn to start and see what the reading is. Pretty sure Tonij1960 already asked this so.....

Rocket science....... ............LO L.