If you have a back drive through the MS from that other hot at all times line, you could see 12V on WHT/R with a bad main relay. The MSPNP variants are honestly not particularly good examples of Electronics design.

If you have 12V KOEO on WHT/R with the MS connected, and you don't have it with the MS removed, this is almost certainly what is going on. The MS has no role in energizing the main relay. There is a remote possibilty that modification to the cooling fan circuit could cause an interaction between the main relay and the MS if that applies.

next step is to confirm the engine fuse is still intact

 

Fixed it. Thanks to Gooflophaze. Two years ago he gave me a spare main relay.

The main relay had a PARTIAL failure. It would make enough contact to register 12v on the multimeter but not flow any amperage. That's why so many things didn't make sense.

It cranks and runs now. I'll see if it connects to the laptop in a few.

Thanks to all of you for your advice and emotional support during this personal crisis.

 

~cough~

 

"I pulled the seats out and replaced the carpet and harnesses."


Recheck your work

 

Thanks for the direction, Ted. Your suggestion is why I checked the voltage at the injector harness to start with. I wish it had been zero initially because it would have saved a lot of hunting and disassembling. How did you know that could be it, personal experience?

 

Good advice. I should put a wrench on everything again.

I'd like my sub belts to be half an inch shorter but I have to remove the seat to reach it (6pt harness). Not feeling motivated this evening. Maybe tomorrow night.

 

I have a degree in EE and specialize in troubleshooting complex electronic systems. I am also intimately knowledgeable of early NA electricals.

Pretty simple really, what point of failure will result in the symptoms being described. Start there, move out.

 

I've learned don't add any more taxation to the ECU circuit. Always find switched 12v from other sources. Why Mazda decided to run so many high amperage things through a single relay is beyond me