I use these motherboards, and they work fine! Just take this cable that came with the Cruise Commander and retask it for the 4-pin to 3-pin duty. You can just find a 3-pin connector shell and rearrange the wires.
That cable and the speaker is all you need. You don't need the battery or the RS/SS switch. If you don't have any old TMCC connectors laying around, they're available from Digikey for peanuts. They have all the JST EH housings from 2 pins to 10 pins in stock: http://www.digikey.com/product...&pkeyword=jst+eh
The matching pins are on each product page.