elec. fuel pump relay wiring diagram

If you get it backwards, and there is a diode, the coil won't actuate w/ 12 V since the current will flow thru the diode. If you do it very briefly, you may not damage the diode. You can hear the relay click. To tell ahead of time if there is a diode, measure resistance w/ a multimeter, and you should measure low one way (<100 ohm?) and high the other way (>1000 ohm?). But, should be a symbol on the relay if it has a diode. When a diode fails, it usually fails shorted.