ignition switch problem
 

On my 1968 912, I am having trouble with the ignition switch. The engine will start when I put the trickle charger on and drive the car for a while, then turn the engine off & try starting the engine and it is completely dead. The battery was tested & is good. where should I start to find the problem? I was thinking of installing a push button switch.

Is your generator light going off when the engine starts? First check your cables are clean and tight, the long positive one to the starter, the ground where it connects to the body in front. Then check your generator and voltage regulator.
Are you absolutely certain your battery is holding a charge? Buy a cheap multimeter (HbrFrt) and see what kind of voltage you have at the battery with the engine running. A good move would be the installation of a starter relay -easy and cheap to do.
Bill

I had a similar problem where the starter only would click or do nothing at all except when I had the battery charger connected. I bought a new starter hoping it would solve the problem, without luck. It turned out to be coroded terminals on the battery. Cleaned them with some electrical cleaner and it worked like new.