Fresh water pump

[1960Aerocraft]

I have a problem with a fresh water pump that is really baffling me.
If I take it out and hook to a battery it will run. When I plug it back into the socket on the boat it doesnt run. I have checked all the wiring, checked for voltage at the wiring, which is about 11 volts. If it isnt plugged in and I flip the water system switch on, I will get the little light on the panel which says that it is on. I then plug the water pump in and the light goes out. I have the polarity correct and just dont know why it wont work when plugged in. Any ideas? It is a shurflo pump
Thanks in advance

 

[Bob's Garage]

Re: Fresh water pump

Who wired in the switch/pump? It sounds to me as if the socket (?), or switch, is shorted, and when you plug it in it opens . Otherwise the light should not go on.

What kind of switch and light set up? What kind of socket? How many wires?

Current should not flow thru the light until after going thru the pump.

 

[1960Aerocraft]

Re: Fresh water pump

As far as I know it looks like it is original. It is from the mid 80's. There are two wires in the plug on the positive side that goes to one wire on the plug on the pump and one negative wire on each end of the plug. The switch is mounted in a panel that has lights, etc. All looks original. The switch is an on /off type with a little light above it. If the pump isnt in line and I put the switch on, it lights up, when the pump is in line, it doesnt work and the light is off. Could you suggest where I start to look?
Thanks

 

[sccatfish]

Re: Fresh water pump

Sounds like you're not getting full power. There's enough power to have the light on, but not enough to turn the pump. Could be a corroded connection somewhere or a bad or uncharged battery. With a fully charged battery you should have over 12 volts.

 

[JoLin]

Re: Fresh water pump

Sounds like you're not getting full power. There's enough power to have the light on, but not enough to turn the pump. Could be a corroded connection somewhere or a bad or uncharged battery. With a fully charged battery you should have over 12 volts.

+ 1

 

[generator12]

Re: Fresh water pump

Classic case of resistance in series with the load. I'll bet that if you strip a very small section of the wires to the socket and check for voltage with the pump plugged in and turned on, you'll find that the voltage is down to nothing at that time.

You've got either a high resistance switch (my vote), a seriously bad connection, or a wire frayed down to just a couple of strands.

Try jumping a wire (use alligator clips for ease) from battery positive to the switch. If it still doesn't go, jump the pump negative to a good ground. One or the other will make it work and you'll know which wiring needs correction.