Gene- I have a 188 with the same problem. Since day one I have no depth readings on plane. My TD is mounted in between the first set of ribs next to the motor. When I started looking at why mine wouldn't work, I found the little welded trim tab directly in line with it. Another spot has a bunk board there and it seems like each opening for a TD is blocked by something. I've thought about buying one of the set back mounts that put the TD about 8" behind the transom and (supposedly) into clean water, but the lakes I fish are filled with stumps. Let me know if you find a spot.