Perplexing pump problem

[muskyfins]

Installed a new fresh water pump over the weekend. (although the old unit might have been good). There's some sort of electrical issue.

When jumped directly to the battery, the pump runs as expected. (it runs but we haven't let it run long enough to build enough pressure for it to switch off)

When we checked the leads from the switch, we showed 12.59 volts which is exactly what we had at the battery itself. (battery was getting a little low)

When the pump is wired to the leads, it won't run.

Then I checked by connecting the positive to the pump and running the negative straight to the battery and nothing. (in case there was a ground short)

Any ideas what is going on? Not sure if this is coherent, but please feel free with questions or suggestions.

 

[Scott Danforth]

Check voltage at pump with switch on. I bet the voltage drops indicating a bad connection in the curcuit

 

[Silvertip]

If this is a "demand" type of system, there is a demand switch in the system. Bypass that.

 

[muskyfins]

Check voltage at pump with switch on. I bet the voltage drops indicating a bad connection in the curcuit

12.59 volts. Same as at the battery directly. Very little voltage drop.

 

[muskyfins]

If this is a "demand" type of system, there is a demand switch in the system. Bypass that.

I don't think I have any other electrical connections (demand switch) I believe the pump runs until it pressurizes the lines and then shuts off. When you open a faucet, the pressure drop in the lines causes the switch to turn the pump back on and provide pressure. When you close the faucet, pressure builds until the pressure switch kicks off again.

Is there another switch? Where would I look? I can track the plumbing until it goes through the bulkhead into the cabin.