I used a water switch from a washing machine. I don't remember the size of the
PVC cap but it was used by a lot of the local shrimpers in their old wooden
boats ( read leak a lot ).

The switch is usually in the control top part. They recommended using a
smaller longer hose and mounted the switch high on the bulkhead.

Mine worked for a little over 5 years with out problems. ( Sold the boat ).

It would take a little experimenting but easy engulf to find the cap size.
They heater a brass hose barb and just screwed it in to the hole, I drilled &
taped it. It isn’t boat pretty but very useful.

For the delay the Radio Shack idea seems the best.

Mike.
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However I am sick of replacing bilge pump switches. ( I have a
shed full of floats!)

I thought to seal a mercury switch and put it on the float when
the float goes up the pump comes on (through a good relay)

However the switch comes on the pump runs for a very short time
and just clicks on and off driving the relay crazy.
I need to have a delay that will keep the relay pulled in say
5 to 10 seconds before dropping out and resetting.
Anyone have an idea or circuit that will do this for me.
Thanks
Oliver Fleming