Actually the best way would be to put the second pump in parallel to the
Insert a "T" fitting in the supply line ( the one from the tank) to feed
both pumps. A second "T" in the output line to take care of the second pumps
Wire the second pump to an independent switch so that it isn't powered
normally, but can be turned on in the event of failure of the "primary" pump.
With good quality pumps, the check valves in the pumps will take care of the
backflow problem, so long as the second pump has about the same output as the
We've done a couple like this for endurance type racing and so far no
problems. I've threatened to do the same on my street car, but the pump I've
got now hasn't given any problems in the last 4.5 years, Soooooooo, I haven't
bothered to get under the car and actually do it.