This all started with a noisy alternator bearing and a sticking starter motor. A starter was acquired from ebay and that’s fine but the alternator was the start of weeks of pain.
I got a new alternator from ebay which when fitted made some odd whistling and after a brief test round the block the car promptly died. Turns out that after having the new alternator tested it is faulty and pretty poor quality.
I had new bearing put in the old alternator and refitted it but we’re still dead. The 80 Amp fuse was blown so I fitted a new one and we’re still dead.
After a bit of testing it turns out the engine management fuse was blown. Fitted a new one and it blew straight away. The car is fitted with a DIYAUTOTUNE megasquirt. So not straight forward to diagnose but at least I can talk to the ECU with a PC. I took the ECU out and put it on the bench to test. All checked ok.
Then I go hunting for a wiring diagram. Eventually I found a really handy document which is here if you need one. Mazda+MX-5+Miata+2000+Wiring+Diagrams
Slowly working through the wiring diagram I isolated all the engine wiring loom eventually and the problem was still there. In desperation I hooked my meter up between the failing circuit and earth and disconnected every plug I could find one by one until the meter showed open circuit. Eventually I found the part of the loom that had the fault.
By this time the car is in lots of pieces and spread all over the garage floor.
Could not see anything obvious in the loom and then without finding anything at all the thing starts working. Now I don’t know what worse, having a fault to find or having it working and not know what the fault was 😐