Strange things are happening to my '83 240D.

Symptoms.
- battery voltage 12.7v engine cold, at idle.
- battery voltage 13.5v engine cold, at idle, glow plugs disconnected at preglow relay timer. (I haven't tested the voltage with the engine warm to see if the glow plugs 'switch off'. Are they supposed to switch off after a certain time or when the engine is warm?)
- dash clock doesn't work when the engine is running, but does work when the engine isn't running. (strange!)
- preglow dash light comes on only every now and then. Doesn't seem to affect whether the preglow works or not. The engine starts just the same.
- glow plugs draw about 20 amps each when connected one at a time from the preglow relay timer clip.
- glow plug resistance 0.6 ohms each. (they're wired in parallel)
- preglow relay timer is hot after driving for a while. The 80 fuse gets hot very quickly when the ignition is switched on. I only have a 10 amp multimeter so I couldn't check how much current was being drawn.

- dash seatbelt warning light flickers on every now and again. (this has been happening since I've had the car. I've just ignored it)


History:
The battery and alternator were replaced last week. At that time the preglow timer relay would buzz for a while whenever it felt like it. The buzzing seems to have stopped since the new battery and alternator. However, the symptoms above, especially the clock and preglow light both started a few days before the battery died.

ALready checked:
- grounding wires at battery and from engine to chassis have been repaired and checked. 0.9ohms resistance from chassis to engine. IS that OK?
- Checked and corrected all the fuses in the fuse box. Some of them were the wrong fuses, so I corrected them.

questions:
IS the preglow relay timer testable? How do I know it is good, and if's not good, is it repairable?

Does this sound like an electrical short? HOw do I diagnose it and find the problem?

What I really want to be sure of is that the glow plugs aren't drawing massive current all the time the car is running and damaging my alternator and battery.

Thanks for any help, I 'm at a loss here.