My 88 "stock" non DD sammy's battery light stays on constantly. The problem began intermittently about a month ago. The light would go out at higher engine speed and now stays on all the time. Two weeks ago I checked the alternator output and it was then at 12.3 volts with the battery light on. Now it is down to 11.75 volts so the alternator is not charging. There no change in the output with the headlights on and the heater blower on high.  With the engine off the battery voltage is at 12 volts. The strange thing is it has never failed to start. Any ideas what could be going on?

Your alternator is dieing a slow death, but on the plus
side, you can jump start these little trucks with a motorcycle
battery, so if you have a beefy battery and a little charge
to help keep it going you can run a long time with a bad Alt

Wild

Leave it long enough like that and it WILL fail to start - the alternator has some output, but not enough to properly charge the battery - take your pick, worn brushes, a defective regulator or defective diodes - those would be my guess - if you're handy you can disassemble the alternator & replace the brushes, but anything other than that is probably beyond the skill of most backyard mechanics.

I ordered a reman alternator through our local parts store and will install it tomorrow night. Thanks for your input.