Powered Subwoofer troubleshooting

Hi all. New here so I hope this is the right place to post. I have a Pioneer slimline subwoofer installed TS-WX130DA. It has been working mostly fine, every now and then would not come on but would be ok after hitting the reset switch. Now it doesn't work at all.

First step in troubleshooting was to check the unit is getting power. It has a power connector with ground lead (black), permanent 12v (yellow) and switched 12v via the ignition (blue). This is where I stopped troubleshooting. If I measure voltage with the plug disconnected, everything is fine. As soon as I plug it in to the subwoofer, the permanent 12v drops to 2v and then gradually increases over time up to 12v but the unit doesn't power on. If I switch on the ignition, the blue comes on at 12v, and the yellow drops to 2v and stays there.

I tried adding an extra ground lead to the connector and that didn't help, there is continuity between the ground connector and a metal part of the body, measured ~8 ohms between the connector and the door latch.

Is the unit cooked? It just seems weird that the voltage drops that much, I can't imagine where the current is going...

WHere did you get your power from?

Also if you are getting 8 ohms, that is way too much. You should be way less than 1 ohm of resistance for your ground, preferably 0. Make sure to measure the internal resistance of your DMM by just touching the leads together then subtract this out of the total measured resistance.

You have a weak point somewhere down your power cable, it’s causing voltage drop… be it a crimp, fuse, wherever, or also could be an earth if you are using the amps black cable for the negative multimeter lead, test with a good earth on the multimeter if you’re not already… you may find the earth is floating up away from earth and not the power

assuming the earth is ok then use a good earth and test at joints with the amp connected and drawing current… along the power cable… normally the crimp terminal, in and out of the fuse holder (it may be the fuse itself!) and the crimp at the amp of its crimped

one strand will give good voltage at the end of a cable with no load, but once you put load on it the voltage will fall due to voltage drop across the strand under load

Yep!

Maybe you have some corrosion in the power or ground connections? This might explain it getting slowly worse over time. Follow dumdum's recommendations and look for that weak link.