Hi Jerry, I've been where you are...
Yes, I've replaced the Johnson bilge pumps that came with the Circle T Ranger 29 -- 3 times now. To answer your first question, the water level sensor is electronic, part of the pump -- there is no float switch per se. Initially my problem was that the bilge pump would be submerged in water and turn on, but not pump water. That problem turned out to be the metal drive shaft on the motor shearing the plastic impeller. The electronic sensor would sense water and turn on the motor, but the motor's drive shaft wouldn't turn the impeller because a 5 cent part was too weak to bear the load. After replacing the entire bilge pump (as the impeller alone is not replaceable), it still wouldn't function reliably. The reason this time was that it was not "self-priming". After much head-scratching, I thought this all too unreliable for such an important piece of equipment, so I looked for a different brand of bilge pump.
On the advice of the Ranger factory, I replaced it with a Whale bilge pump. However, after about 2 months I found that I'd show up at the boat and the pump would be running continuously - even though there was no water in the bilge. The Whale pumps also have an integral electronic water sensor to turn them on and off. It would sense water when there was none, and turn on and run continuously, with no way short of removing the fuse to turn it off. Fortunately I was on shore power and not battery power. So I took out the Whale pump...
I finally bought and installed a Rule 500 GPH pump. This pump has neither an electronic switch or physical switch to sense water. Instead, every 3 minutes it just turns on. If it senses no physical resistance to it's impeller turning, it instantly turns off. If it does sense resistance, because there's water there to be pumped, it keeps running and pumps it overboard and then stops. So far I've had this Rule pump for several months and it just works. The power drain from it turning on and instantly off every 3 minutes is miniscule. The 500 GPH model was a fallback -- I initially tried a more powerful pump but it was physically too large to fit in our rather skinny bilge area.
To change any bilge pump requires cutting wires, and then reconnecting them to the new pump with water-proof connectors that you must heat up and melt into place. The old mount at the bottom of the bilge must also be unscrewed and removed, and the new mount installed. If you're not comfortable with electronic connections, and flexible enough to reach the bottom of the bilge with a screw driver, then you should probably hire it done by a professional. It's a quick job for a knowledgeable DIY owner or a pro. Hope this helps.
