Relay contacts get corroded and the coil will pull them in “click” but the current can not flow through the dirty contacts. Swap it with another relay that has the same part number or buy a new one.
the heat from the resistance because of the poor connection will expand the metals and force them together creating better contact and a better path to allow more current to flow allowing the car to start
go feel your cables after you have an episode. don t burn yourself…