Can you temporarily ground the power supply from the battery again and see what happens?
I think I'm running an M3 ATX. This unit has worked perfectly in the past, but since re installing, it will only power intermitantly. I've measured the voltages at the power in and acc trigger wires, both being at about 11 - 12 volt. And both are wired correctly. The only thing that has changed is I'm now earthing to the chassis as oppose to running a negative lead from the battery.
I was thinking that perhaps the unit is going into the battery saver mode or whatever it is, where when the voltage drops too low it shuts off the 5 volt rail. But this doesn't really make a lot of sense as it's not operating consistently at all.
Or the other option... has my power supply died?
TLDR; When turning the key, power supply won't turn on, connections correct.
Since my last post, I've run a set of jumper leads to the end of the car (where the pc is) and measured the voltage, which turned out to be near on identical, also connected the jumpers to the PSU and same result. Any other ideas? I may have to post some pics, on my Mobo the PSU doesn't sit perfectly in the ATX plug, theres a capacitor in the way, But as I've mentioned, it hasn't been a problem in the past, i don't understand why it would start now,
the M3 won't turn on if the voltage is less than 12, could that be the problem? not enough power?
I see that you mentioned the power reading is between 11-12, try and use another battery somehow and see if it is still happening
What do you mean that you THINK you're using an M3? That statement means you are maknig an assumption, and we all know what happens when you assume, right?
It sounds like you are using an older PicoPSU which has a similar formfactor as an M3, but requires regulated 12v.