Tech1A and 86 - 89 5.0 5.7 TPI Diagnostics

I cant get my Tech1A to read data from any 89 or earlier Corvette. I have the right cartridges and the the F and Y body adapter for TPI engines. It will flash the engine light and flash the code 12. it will also go into "field service mode" but other than that, when I try to get data I get the message" Waiting on Data" thats all. I am thinking either the y body adapter is bad or the DLC cable is the wrong one for this car (is there another?) ..it works fine on any other car other than TPI 89 and older. Can anyone tell me what the problem is? snipped-for-privacy@charter.net