What a fun day I had. Fairly cool out this AM So I thought I'll get the lawn mowed. So about ½ way through I stopped to grab a small branch that had fallen. I forgot to shut the PTO on the tractor off so it shut the engine off when I raised up off the seat, Gotta love the safety features 😉. So, I jump back on hit the key and nothing, nada, ZERO. Hmm, must've blown a fuse. I proceed to locate the hidden locations (can't put them where they're visible or accessible). All appear good.

So get the other tractor and tow if up to the shop as its acting a bit strange with the warning lights sometimes coming and sometimes not. Get out the schematic and begin 5+ hours of chasing my tail. Battery Voltage is OK at 12.5. I proceed to chase the V to various relays and switches. After it sits for a couple of minutes everything is normal until one hits the glow plug warm up (diesel) or tries to start it. THERE WAS A BIG CLUE THERE
I suspect something is causing a draw and there is a delay timer in the power circuit that I'm still not quite sure what it's purpose is, but suspect it may be faulty due to the way the dash lights etc. are acting. It bench tests fine. However the voltages at the connector are acting a bit strange. SEE ABOVE 😉. I begin disconnecting / bypassing thing looking for the DRAW. Eventually I get all the way to the starter. AH HA, if I disconnect the solenoid, all seems well. I try a remote switch on just the starter and NADA. Shorted solenoid? I scratch my a-s a bit more and start hooking some of the items back up and removing the bypasses. Things are good until I hook the glow plugs back up. Almost back to square on but not quite? Scratch a-s some more, smell fingers for good luck . Test all 3 glow plugs. They test fine. WT-O??? At this point I have tested about everything I can think of including multiple V tests. I leave the DVM hooked up and proceed to discover that as soon as one puts a significant load on the system the Voltage drops rapidly to about 2.5V. once the load is removed it climbs back up to 12.5 in about a minute. Bad Battery?[b] Yes sir[/b]. In over 50+ years I have have had a few just magically die, but never had one that would recover V wise as this one did and act this way.
Almost forgot to mention that at one point I was going to finish mowing with the big tractor at which time I discovered it's new alternator put on during the winter was no longer functioning.
GREAT DAY 😊 Hoping yours was better