I want to thank everyone for their hints on this conversion. It went better than I expected, in part perhaps because my Autohelm ST50's were 'plus' models. Special thanks to Pat and Steve: Steve, thanks for the hint about opening the jaws of the spade connectors. They are fussy enough without the PITA of trying to push them on when too tight! And, Pat, I would have been really perplexed about my depth if you hadn't warned me about the hook up. I had a three-wire transducer hook up on the 50, but it didn't work. I swapped what I thought was the screen and another and it works like a champ. I may put in the new transducers next haul. The speed looks like it would foul a lot less and the depth looks better too. Anyhow, I'm still annoyed I couldn't get a competent tech to work on the old system but at least I have a functioning system again. Rick D.