I just put new headlights in my 1978 300CD. Within a couple of days, both high beams "blew". There was kind of bright flash and they were gone. Low beams are still fine. Fuses look to be OK. What would cause only the high beams to go out like that?

Thanks in advance.

 

Since the chance of buying two bulbs that are both faulty is pretty slim, my guess is that perhaps you installed bulbs that were not properly rated for the car.

 

Actually, they are the correct ones. We are trying to track down a loose connection which might be causing a short, or a surge. There are a few other electrical issues at this point, such as the blower motor fuse melting. I will post once I have it nailed down.

 

Seems to me if the bulbs are blowing and the fuse is not protecting them, it's rated to high. Verify the fuse has the correct rating so you don't keep losing bulbs and possibly start melting wires.
For a short on the headlight circuit, have you checked the combination switch on the steering column?

As for the fuse getting hot on the blower circuit, check the actual draw of the motor. It may be that it has a heavy draw or short in the motor and overloading the fuse.
Check for proper ground as well.

 

On the right (seated in the car) sidewall in the engine bay there is a resistance coil for controlling blower motor speed. Make sure all the connections and grounds for it are good and that it has good continuity through the coils.

Also, check the alternator to make sure that the voltage regulator is working and make sure you have the correct alternator installed. I believe it should be the 55amp and not the 65amp unit.

It's very rare to have components suck too much amperage in a negative ground system. Everyone who has ever had a British vehicle will know exactly what I mean.