Problems With 911 Tach and MSD

[Mario.D]

I instaled a 911 Tach in my VW Kombi Bus 911 2L S and MSD-5 ,& the tach
have a malfunction when is conected.
The problem disapear when don't use the MSD.
In the past i used a normal VDO tach with a same MSD-5 without problems.
Somebody have a idea wich is the problem?
This engine use a stock distributor with point & condenser and the MSD-5
is to use with point.
Maybe a Porshe 911 tach is not to use with a MSD?

Regards.
Mario