I would suggest finding a better socket design if you want to use a
pump with a 12V outlet.. Remember that 4A rating is often an un-loaded rating and every manufacturer rates these small pumps differently..
As an example a while ago I had a brand new
Rule 500 kicking around my shop so I attached it to a
battery...
Rule recommends a 2.5A fuse for this
pump. The fuse is sized to prevent the pump from caching on fire.
Battery = Group 31
AGM Resting Voltage 12.77V
Meter = Fluke 376 w/Inrush & min/max NIST Calibrated, Fluke 289 & Fluke Infrared Pyrometer
These are the tests I ran:
12.75V - Ran pump dry for 10 minutes and saw 1F rise (Fluke Infrared pyrometer)
12.72V - No Load (spinning in air) = 0.7A with no load (in-rush/startup current current = 2.7A)
12.72V - Pumping
water, open bucket rate, no
head pressure from hoses 1.34A (did not test with hoses, elbows etc. but would likely be a bit higher)
12.72V - Locked Rotor with a 3A Fuse = Blew Instantly
12.71V - Locked Rotor with 5A Fuse = Blew nearly instantly (about 6 seconds)
12.71V - Locked Rotor with a 15A Fuse = No blow 10.9A continuous draw, pump getting rather hot to the touch after 90 seconds of stalled rotor. Discontinued at 2 minutes and 10.7A (heat build up in windings likely caused current to drop a bit)
bilge pump was at 136F, and climbing, at 2 minutes of stalled rotor.
12.70V - Locked rotor measuring inrush with 5A ATC fuse - Inrush = 10.9A - Fuse blew
You would be well served to use a DC clamp meter, or even a DVM set to 10A scale, in series, and measure the pumps actual current draw before continuing to run it off a 12V socket. As can be seen a 4A rated pump may not be a 4A draw. If it stays below 7A when pumping
water it
should be fine provided all contact points are
clean and the male plug fits
tightly.