Converting TBI to carburetor issues

I'm currently converting my 89 3/4 ton dodge from a TBI to a carb. We have traced out all of the wires, figured out the auto shut off relay and have power to my coil. But, the orange and grey wire that feeds into the distributor is where I'm stumped. The orange wire is hot. But we can't get a ground signal threw the grey wire. The distributor was changed from the original 3 prong hook up to a two prong. What has to be done to get fire to the distributor? Can I bypass the SBEC some how?