Here's how I solved my SM fresh water pump problem:
I am always VERY reluctant to change anything on my SM because Amel always does everything for a good reason. But after reading of all of the many options and considerations to solve fresh water pump problems I solved my problem by using a different pump and am very, very pleased with the result.
If you're a good mechanic like many of the best advisers on this forum are then you may just as easily follow their instructions and adjust, repair or replace the "Square D" pressure switch. But after spending several frustrating hours on this I chose to go with a simpler solution.
I removed the factory A.M.F.A. pump and small 'surge-tank' and replaced it with a "Shurflo Aqua King II Premium Fresh Water Pump", Shurflo part # 4158-163-E75. Cost was about $220.00US. (You will also need Shurflo part # 244-3936 Pump Fittings/Adapters, 1⁄2" Female NPT Wing Nut to 5⁄8" Barb , Elbow
Swivel Fitting, about $3.00US)
I left the Amel accumulator tank in place so the new pump does not cycle for small things like getting a drink of water.
After removing the old pump and small tank all I had to do was hook up the input and output hoses and the (+) and (-) wires. To make it so that the green "pump on" light comes on, connect small black Amel wire to the red wire that goes from the front of the new pump to the back of it.
This system provides 55 PSI and taking a shower is now just like taking one on land, with no fluctuations in pressure, and lots of it.
The pump is designed to prevent cycling so that at low demand it takes some of the output water and returns it back to the input (kind of like a 'wastegate'.) This way, although the pump does come on sooner than with the factory system, it doesn't cycle on and of very much at all. I've only had this system in place a few weeks but so far am completely satisfied and actually prefer it to the old system.
SM 384 Sirena Azul