I've built 2 with Icom mobiles and 1 with a Kenwood mobile. In these applications there are 4 connections to the radio.toggle quoted messageShow quoted text
External speaker provides audio out and ground, the mic jack provides ptt and audio in. Based on what I've read, if you have a yaesu with the 6 pin din on the back it is a direct plug in (not 100% sure on that one).
If you don't have the little AVRT7 Plus display box, they are now available on ebay and I would highly reccomend getting one (I built two when they weren't available and just bought 2 more). They make these far more enjoyable and easier to troubleshoot but are not required.
Let me know if you need any help getting everything set up. These certainty aren't an easy plug and play experience but when they finally work they are an awesome tool.