About a week ago is was driving my 1984 300d home from work. It was -1 F if that matters. Anyways after about 4 miles of mixed driving my radio started to act up. After about another mile the battery light turned on but really dim and the radio went out completely. Finally I made it home turned off the car in my garage and attempted to start the car because I know that these cars can run without a functioning battery or alternator. The buzzer also sounded odd. I waited for the glowplugs to warm and cranked. It went crank pause, crank pause, crank and gave up. Tried again with the same result. I got out my jumper cables and attempted to jump it with my land cruiser. Same result strangely.

I swapped the battery out of the land cruiser into the 300d. It started like normal but all of the dash lights were on dim (brake, battery, ect). I drove it around the block and the temp and fuel gauges were going full crazy and were all over the place. Headlights did work they I cant remember if they were dim or not but either way it wasn't enough for me to notice.

I pulled a good relatively new battery from my parts car and installed it. I tested the battery and it was at around 12ish volts (I have a analog multimeter that can be kind of hard to read) I drove it about a mile before the gauges started to act up. Another thing is the gauges appear to read accurately when the car is in park sometimes. I have tested the battery with the car running a number of times since and though it is kind of difficult to read the multimeter I can tell its not close to 14v.

I went look at the voltage regulator but i was unable to because of a coolant hard line in the way of one of the screws. Also I plan to get a digital multimeter later tonight and test with that.

Any thoughts or ideas on what these issues could be?