yep, me too.
could be fuse box itself as you might think, could be dodgy plug/wire underneath too, or still a bit of rust/scale/muck in the pin sockets ..
When you wiggled it, did you feel it click. It would have been clearly obvious if it did. Theres a difference if it did click or not click.
if it didn't click and the pump suddenly sprouted to life, then the main power(ie. pins 30/87 .. or 3 and 5) are the issue to be looking into.
If the relay clicked, and pump came on, then the power for the relays coil is where to look into.
remember the relay is just a fancy schmancy switch. Your switch(in this case, the key powering the main relay, so no actual switch to speak of) .. powers the coil in the relay, which connects the main feed to the pump.
think of it this way: you have a simple switch to operate a device(say lights, or sunroof, or whatever). the switch you use to turn it on/off will be made cheaply/small, dinky as possible(to save money) and can't carry a large current load.
So there is a relay between your switch and your device. The switch activates the relay switch(ie. the coil) and the device itself gets power from the battery but via the relay. the coil in the relay just connected the main power from battery to relay to device.
reason for all this is that if you push say 30 amps that a device may need via a switch that can only carry 1 amp, you burn the 1 amp switch out quickly. The coil in the relay only needs say 0.5 amps to switch(from on to off or other way around) and it then switches the actual switch for the main power to the device.
This is what a relay is, and why they're used.



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