What's up with this??

I replaced the coil on Volksiebus with a brand new Bosch coil - VW
spec'd.  The tach worked right up to the point of change, when I
disconnected the wires, installed the new coil, and reconnected the wires.

Engine starts and runs fine - but for the tach - NO JOY!

Anyone got any  ideas. Everything appears as it should be. It's all
wired back up exactly like the original coil - wires same places. But no
tach.

I haven't done this yet - but I can do a voltage test from the +15 pin
to ground without blowing something up, can I not. Been a long time
since I've had a meter out for anything but a continuity check.

Suggestions appreciated.

Thanks,

John