1973 450sl no start after testing alternator

[Jonchip]

I'm trying to help out my brother in-law on his 73 450sl. The vehicle was starting but the battery was dying and when he would charge it up it would run fine until the battery died. There was no battery light coming on and it was coming on in ignition on then would go off as soon as it started. He told me he was using a test probe and found when it would start he had 13.7 volts until you reved the rpms and then it would go to battery voltage. Now here's were it gets tricky. He's telling me he was probing the 3 wires in back of the alternator while it was running and put 12v into one of the wires and the engine died and will not start now.
I have now got it and I checked all fuses that I know of and they are good. When ign is on the battery light does not come on anymore. I can here the fuel pump coming but I am not getting spark now. Any help of where to go to next sure would be appreciated. Thanks

[Frank Reiner]

Jc:

As a starting point, check for continuity through each of the ignition pre-resistors. Depending on the version of the ignition amplifier, both pre-resistors may be in series on the power side of the amplifier, or one on the power side and one on the coil side of the amplifier. If the pre-resistors are OK, check for power at the coil with key ON.