Is this normal? 1983 300D odd startup dim lights

[psaboic]

As the title says......

I have an 83 300D with roughly 240K on it. First winter driving it. Anyway this may be a stupid question but here goes.

On the first start of the day, or anytime after sitting for over 6 hours, the headlights and instrument lights are dim and the fan motor seems to be running at half speed after the car is running. This continues for at least five minutes after starting (if left to idle), or for about a minute to two minutes after driving. Then suddenly, it is if someone threw a switch.....full power to everything, and all is fine until next overnight start. I checked all connections to the battery and alternator, and the alternator belt is snug an not slipping.

Any clues? I do not have a volt meter installed in the car so unless I get out a DVM I'm not too sure what voltage I'm putting out. Oh yes, the charge light works normal at start up and never comes on during the low power issue to indicate trouble.

Thanks for any help.

Glenn