I let my '93 300D sit for about a month, tried to start it, dead battery, charged it over night, started right up, but no radio (aftermarket, recent install) and no blower fan. but it ran fine. Parked it and ordered a new blower motor and fan speed resistor. Proceeded to take the old fan out, got down to the fan, spun it by hand then turned it on from the inside with the key, it spun, but did not change speeds. Turn it off from inside and it would not turn back on, spin it, then turn it on, it would spin/work again until you turned it off, then nothing when I tried to turn it back on.

Got the new fan (not URO this time) and resistor, swap everything out, turned on the key, fan was on, but only one speed and would not turn off no matter the setting, then after about 15 seconds, everything started to flash and I got a loud clinking under the hood that got progressively faster. Checked it and it is the Glow Plug relay/controller. If I unplug it from the glow plugs, no clicking, try to start it and I get the weak battery clicking, no start.

Cleaned the battery terminals, put the charger back on and it read 100% charged, put the volt meter on it and it reads 12.4 volts.

I checked the glow plug connector to ground and all 5 have almost 0 ohms of resistance (or no resistance) to ground.

Even after cleaning, same thing, if the glow plugs are plugged into the controller, constant clicking, if I unplug it, no clicking, but no start either.

Any chance this is an easy dead battery although reading a full charge? Any other thoughts? I still have not put the wiper back on, trying to get this figured out first before I button everything back up.