My 1986 951 had the starter soleniod energized(stuck on) at my last race event. this issue drained the electrical system and the alternator would not charge the system. I have now replaced the alternator and starter. I have also checked the bell housing grounds, battery connection and alt./starter leads. . I had a full charge on my battery, started the car, ran for a few minutes and then drained the electrical system . When I turn the key to the "on" position there is a drastic voltage drop. Is there a way to test the ignition switch? Is this a good time to run an aftermarket switch for the power and a separate on for start? Any ideas? I need to get this thing fixed and loaded in the trailer for this weekend! Help!

 

If your ignition switch was causing enough drain to flatten your battery that fast it would be smoking and fry the harness in that area. Check your unfused cables between the battery to starter and starter to alternator. You have a dead short somewhere in an unprotected circuit.

 

I have load tested the system and I have now replaced the battery. The car starts, runs and drives. The battey voltage while idling is around 12.3 and the blue wire off the new alternator is around 15.8. The volt gauge on the dash is hovering at 12 volts and now the tach jumps around. Tormorrow I will reinspect the battery cables and the ground on the bellhousing. Any other ideas?

 

I has a similar problem with my truck draining the battery. The way I found it was to put an ammeter on the battery. Then I started pulling fuses one by one until I found the culprit.