Had a similar problem on my 72 ES last year. The engine would start easily, run
strong for about ten minutes until it got up to running temp, then would die abruptly.
Turned out to be the temp sensor for coolant, located on the pass. side of the
engine at the front of the block. It was shorting out when the engine got hot. After
about a half hour or so, it would start up & run fine...but the problem would repeat
itself in when the temp got back up to normal. Maybe someone on the board can
give you the resistance readings for cold & hot so you can check it, or you can
repalce it if you have a spare. Good hunting.

I have a problem with my electrics right now. The discharge red light lights up
when the key is off, possibly showing a short somewhere. I've disconnected, one
by one, all the fuses, the pump relay, the voltage regulator, but to no avail. When
the ignition is turned on (not running, just on), the light goes out. Seems like
there are gremlins in these 1800s.

Chuck