I'm having an issue in the 12V circuit on my 2nd gen Prius (07). The car is completely dead even though the 12V battery is almost new and reads 13+ V, but the main 12V positive terminal in the fuse box reads about 0.4 V. I can start the car by jumping the terminal in the fuse box with a power bank, and then the car runs fine as long as I don't turn it off. While the car is running, voltage at the battery as well as in the fuse box reads 14V, so it would appear that the DC-DC converter is working as it should. I've removed all the crap in the way so that I can get a better look all around the inverter short of removing it, but can't really tell where the heavy wire from the fuse box connects or if there's any sort of relay or something between the fuse box and the battery in the back. Though I'd check here before attempting to digest the endless wiring diagram I have.
So you need to find out why the positive battery terminal that runs from your positive battery all the way up to the fuse box and beyond I guess You need to find out why it's dropping from over 12 volts to 0.4 volts or something when it gets to the front I would think that would be a straight shot right up to the fuse box so you sure you have 12 volts at the battery in the back of the car so I would connection I don't know man I guess you'd have to follow that all the way up where it runs through the car seems to me like there might be problems at the jump spot and the fuse box or maybe the fusible link has burnt a certain seems like something has killed your power at the front of the car if you really have 12 volts at the battery in the back or better If that wire is shorted on something you would certainly know it so I doubt it's something like a common short you'd have melted and burnt wires somewhere.
Thank you for the suggestion and the pics. I did look at that and it seems intact. I assume the white housing for the link is supposed to come out of the black housing? I couldn't get it out to check continuity, but I did probe where the heavy wire exits the black housing and did find 13v. 120A seems pretty big considering it's not operating a starter. Where is that jump point indicated on your schematic? I was trying to find where that heavy wire from the rear goes before it gets to the fuse box.
The jump point is in the engine fuse box. To check the fusible link take it out of the circuit. If you can't get continuity it is blown. It is as simple as the drawing shows it. Voltage can lie because you have the 5 amp monitoring circuit. It is rated high because the battery could be charged at a very high rate for a short time. You replace the whole thing.
The 120 amp fuse link has blade terminals that are secured with small bolts. The sides of the black housing unclip and fold out for access to the bolts so you can replace it. This photo (from a gen 1, where it's very similar) wasn't taken just to show that, but it does happen to show one side folded open to see where the small bolt is on that side (that's how the added red cable in the photo got attached). There's a bolt just like it on the other side, of course.
