When trying to start my 2001 Mazda Tribute V6, all I'm getting is a slight 'click', while the dash lights/indicators etc are all bright. I've replaced the battery (which helped for a day or two) and the car ran fine last night, but this morning it's back to a single 'click' when the key's turned. Boosting doesn't change anything so now I'm thinking it must be the starter motor. Any ideas?

I'm in the process of rebuilding this 1.6-litre diesel Rabbit for my son, and have run into a puzzler that the factory manual isn't any help with. There is a relay socket with 5 wires attached to it under a plastic cover under the hood, near the firewall. I was willing to believe the relay would have been for either the wiper motor or the heater blower motor (they're both in the void under the cover, along with the relay socket), except that all 5 wires pass through the sheetmetal into the engine compartment and into the under-hood harness. This all appears to be factory wiring, grommet, socket and all, not added by a prior owner. Any ideas?