MSD and 1973.5 tach
 

A MSD CDI box had no problem running the tach on my 1973+1/2 (originally CIS based) 911.

Someone once posted they thought tachs after late 1972 would be OK with the MSD output, and my result reinforces that.

I ran a black/purple wire out of the MSD tach output terminal and soldered a hollow (female) pin onto the wire (like the ones in the engine side of the 14 pin connector). I pulled the 14 pin engine connector apart (I have a transplanted 3.2L 1986 engine) and put my hollow pin in the housing, et voila!

That position was not used by anything anywhay on my engine, so no worries there.

The original wire run as shown on the schematic is black/purple, so it was cute that I found the same wire color.

There are several threads on this issue and they can be found with some keywords in the search button field.

Bon Appetit!