Tach problem on 80q Turbo Conversion

[blarson at Zeiss.com]

I am helping my friend finish his 1990 80q that he put a mc-1 motor into,
and even though the car seems to be wired exactly the same as my 1988 80tq,
we can not get his tach working.  The car runs and starts fine, so there is
a tach signal to the fuel pump relay, and the fuel pump relay ground is
working correctly.  And the power and ground to the MAC11 seem to be
working fine.

Car: 1990 Audi 80Q w/autocheck system.
Turbo Conversion Motor: MC 10V w/MAC 11C.

Description of Issue:  Turbo conversion is done and the car starts and
runs, but the tachometer does not work.  The violet/black wire from the 5K
kostell 14B connector is connected in the green/black from the T26
connector under the instrument panel.  Troubleshooting performed to date
involved swapping instrument clusters and verifying the signal from the
violet/black wire.  The wire is putting out a voltage and the instrument
cluster swap did not result in a working Tach.

I am wondering if anyone could make some suggestions on what to try next?

Also, has anyone gotten the dynamic oil pressure system working correctly
on a turbo converted car?
Thanks,
Brian
Saint Paul MN