[TR] Electrical diagnosis: Update

[KingsCreekTrees at aol.com]

Hi all; thanks everyone for your input.
 
I've followed everyone's advice. Before I did anything, though, I removed,  
cleaned and tightened every battery connection (at the battery terminals, 
the  battery ground connection on the block, the connection at the solenoid, 
etc.).  Then I tried cranking the car. It was perfect (this is with the old 
Volvo's  battery still fitted). Then, although this was probably not 
necessary, I turned  on the headlights and went through the testing procedure as 
recommended by  Randall (grounding the multimeter to the bulkhead/firewall, 
except on the  battery where I put the multimeter pins on the battery 
terminals). 12V  everywhere, no problem. I thought I'd cured it by re-making one of 
those  connections, so I put the TR battery back on, made sure the 
connections were  immaculately clean again, and we were back on-fault, with no 
cranking, no  ignition light (actually, it did glow once). Foolishly, instead of 
then doing a  bunch of tests, I took the battery out and put the old Volvo's 
battery back  in. Back to cranking perfection now.
 
Both batteries show 12V, which suggests to me that the TR's battery is not  
faulty. This leads me to start thinking that wherever the bad connection 
is,  corrected itself a couple of times, coincidentally when I fitted the 
Volvo  battery.
 
I have to get back to work now, so no time to do any other tests until this 
 evening. In the meantime, I'll be driving myself nuts trying to figure out 
if a  battery can fail suddenly, while the engine is being cranked and 
suddenly the  ignition light goes out and the engine stops cranking, and also 
even if that can  happen then I'll be trying to figure out why the TR's 
battery is still showing  12V.
 
Tonight, I'll put the TR battery back in, then do some tests. Weird.
 
Tim