No tach with crane hy6
 

I put in my crane hy 6 and it runs fine but no tach I tryed it in with the neg wires to the box and I tryed the green tach output from the crane box with no luck it has vdo tachs and a vdo syc guage.:(

tach output
 

Crane has some adaptors for tack proublems. You need to specify which ignitions system you are using and which model crane HI6 box you have to get more help from someone with the same system.

Their HI-6 online instructions include some adaptors

FROM CRANE: If your tach still does not work, you may
require a tach adapter. If your HI-6 is triggered via the
white wire from points or the output of an electronic
system, you should use P/N 6000-8910. If your HI-6 is
triggered via the magnetic pickup cable from a magnetic
pickup or crank trigger, you should use P/N 6000-8920.

I'm having the same proublems with a used MSD box. Ordered a new one and I'm waiting for it's arival to see if that is my proublem.(The box also isn't providing extra spark at low RPM)

The crane unit is plain hy6 hooked to a thunderbolt 4 with the module hooked up using the coil connections to the input red and white wires to the box. I have tryed hooking the gray tach wire in with the neg input to the box and hooking the gray tach wire to the green tach output on the crane box. I have very good spark eng runs fine but no tach has VDO syc guage also inop.Wired according to figure 2 in there instructions for basic module or points hookup I am using the crane LX92 coil.:(

I had the same problem with my MSD ignition and my VDO tachs.All I had to do was buy the adapters and both tachs worked fine.I bet that is your problem.
Fish

adaptor time
 

If you tryed hooking the tac grey to the grey coming out of the thunderbolt ignition amplifier and going into the white HI-6 wire I'd say your stuc buying the adaptor.

HI-6 Tach Adapter For Module Trigger Applications

Part Number 6000-8910

Required for some 1981-1995 non-OBD II applications triggering the HI-6 from the stock electronic ignition module. Connects to trigger input on HI-6 and feeds high voltage pulse required for tachometer and fuel injection operation back into the stock engine control system.

I have 2 of the 8910 tach adaptors on the way I will post here if it takes care of the problem. I need one ram for the Gaffrig mufflers and change the oil in the new blower motors clean the interior. This whole deal has been one big pain in the ass and to think it ran fine a couple of months ago!!!