Yesterday, my 300D cranked very slowly at the grocery store. I headed over to Jiffy Lube and had them put their tester on, suspecting a bad battery.

They told me the battery is fine, and is getting charged OK. Sure enough, when I cranked it afterwards, it cranked just fine.

It was fine earlier today, but on the way home tonight, the lights were getting very dim at idle. I pulled it into the garage and shut it down. I noticed that when I turned the key off, the inside light got brighter. Then, I turned on the headlights, and they were nice and bright. When I turn the key to the on position, though, everything gets dim. Turn it back off, and everything is bright again.

The alternator light has not come on at all, not even dimly. When I had a bad voltage regulator, it would glow.

I would think it might be a shorting glow plug, but I wouldn't think they'd be on after driving for 20-30 minutes.

Any ideas of things to check?