Intermittent total power failure :,(

[flappybaps]

Hi again folks. I have a thread on here already but it got a little messy so I'm gunna start a new one to try and clean things up and get to the root of my problemo. Basically I have an almost total power failure (just a faint ESP light). Tried a new battery even though the old one still reads 12.4V. Did the normal alternator tests and the parasitic draw test. All good. Battery ground is good and I grounded it to the engine block as well. I followed all the positive supply leads around the engine bay and all seems good. Car had an engine swap before I owned it, but I've gone over all the wires and connections that I can see and tidied them up and not found any faults.
He's a weird thing... after leaving it for a week with the battery disconnected, I hooked it up and it started without a problem. I let it run for a bit. Turned it off and had some dinner. Went back to it and it was dead again. But the battery was still 12.4v.
From researching the interwebs all I can find is it could be the ecu (which I've looked at and it looks.. like an ecu. Fuses in there are good), ccm? (Not looked at that), or could it be some fuse or relay behind the interior fuse box? How to test if power is getting to the fuse box? I have a multimeter. I'm not ready to sell a kidney to afford a shop poke at it for days.
Really hoping to get some more feedback from you smart peoples:-) thanks

[SimbadCA]

You've indicated that the battery dies without the engine running; Turn-OFF everything, including the door lights.
Disconnect the battery +pos lead and measure current thru your multi-meter. Select and remove a fuse and observe the multi-meter. "Other" smart people here can give some guidance on what a normal flow of current would be.

[Luis_Heineken]

He's a weird thing... after leaving it for a week with the battery disconnected, I hooked it up and it started without a problem. I let it run for a bit. Turned it off and had some dinner. Went back to it and it was dead again. But the battery was still 12.4v.


Sounds to me a starter problem

[flappybaps]

You've indicated that the battery dies without the engine running; Turn-OFF everything, including the door lights.
Disconnect the battery +pos lead and measure current thru your multi-meter. Select and remove a fuse and observe the multi-meter. "Other" smart people here can give some guidance on what a normal flow of current would be.

Ok that's a new one I can try. I opened up the knee panel and looked at all the relays and big fuses there. All good.
I don't remember saying the battery 'dies' because I only meant to say I didn't have power. In my previous thread I considered a parasitic draw, but the car started without charging the battery, a week after the car was dead.

As for a start motor problem... would that cause total power loss even to hazards, boot latch etc?