Currently have msd distributor and 6al box but tach doesn't work . I have 2 purple wires and 1 grey on the motor was wondering if I should have 2 grey wires ? Have the red wire on the box hooked to the purples and the grey wire on the box to the grey on the motor . Tach itself may be bad just looking for ideas thanks

Normally there are 2 wires on the (-) of the coil, one to the tach and one to the thunder bolt ignition module. I don't know how your setup now, but the wire from the tach needs to be on the negative of the coil.

Other threads talked about hooking the grey wire to the msd box but no definite answer coil would be worth a shot , probably wouldn't hurt anything ....

Where is it hooked now, to the block? If do you do it won't work, I think you should put it on the - coil

Grey is currently hooked to the tach wire coming out the msd box but no tach reading

Tach wire goes directly to the 6AL box. There's a recessed male spade output terminal.
No tach wire to the coil in this application.

Ok so tach must be bad anyway to test it ?

No, you may need a tach-a-dapt made by MSD

My tach gauge is original to the boat 88 year , I thought the adapter was for newer guages ??

I don't really know. I'm no expert. It has something to do with the trigger signal. I have had 2 boats where I installed complete MSD systems. Both boats I owned and ran before the installation. So, I knew the tach's worked before hand. My first boat after the install the tach's did not work. Installed the tach adapters and they were fine. My present boat the tach's worked after the install!