Don't want to add another wire if I don't have to; without pulling the whole thing apart, can someone direct me to where it ties in to the chassis?

Thanks.

The main one is where the battery ties to the chassis right behind the battery to the inner fender wall.

Thanks Stu, I'll check that out.

The 914 has several ground points, in addition to the one at the battery.

The ground for the center console gauges is accessed at the connections on top of the center tunnel, which enters the main chassis harness, and is physically on the divers side firewall under the relay board.

Relay board, underneath in engine bay
Fuse panel, inner fender well, need to drop the fuse box to see it
Battery, inner fender well behind firewall

Front lights are on the inner fenders up in the front trunk

I think there is one more common ground point under the front cowl for the heater/blower/ washer and wipers.

Even better.

Using this info years later, thanks Jeff !

Ditto!
I even laminated a copy to keep in the car!