I think the yellow light is set up to tranny mode... ?? might sound like a stupid question, but have you set it up to the tranny?
Also, Make sure it is set to the correct settings on either legacy (40 meg 27meg crystals etc) or 2.4ghz. What have you done with the first speedo? If that is really not working, then send it back to horizon hobby. I had one with a bit of trouble a couple of weeks back, they fixed it and sent it back no charge.. mine was also out of warranty... they are very helpful at horizon.
Let us know how you get on.
