Triangle VSC (!) Lights on no pending codes

No. There are 2 black plastic ducts that slip into the passenger side of the battery case. The top one connects to the fan. The one that slips into the bottom then connects to another black plastic duct that guides the exhaust air over to the 12v battery well to exit the car. There is a sensor/resistor/whatever you want to call it, in the side of the plastic duct (the one that slides into the bottom of the HV battery). It controls the fan. If you unplugged it when removing the battery, maybe you forgot to plug it back in when you reassembled everything. The flow sensor is located on the passenger side of the duct, kind of out of sight once everything is put together.

This is the duct displayed on its side. What is facing you, is the bottom of the duct. The device directly above the "05 Prius" is the flow sensor. For some reason, all the knuckleheads on ebay have this listed as the upper duct for the HV battery. Maybe that's what Toyo calls it, but I can guarantee you that this duct goes to the bottom of the battery case and the upper one goes to the fan.

 

Does that actually go to the fan? It clips to the fan housing. On all my cars, and some customers, I have removed that connector and spliced the wires together. That connector is very susceptible to corrosion. Although I have never fully traced it out, it was my understanding that connector is in the safety disconnect circuit. I'll have to trace it down one day when I have some extra time.

Looks like you're going to need to splice it also, since one terminal appears to be broken off.

 

I think the corroded terminal(s) is/are toast, even after cleaning.

The electrical wiring diagram (more info) will let you highlight that connector and click for more info, expand the 'wire harness repair' section, and see the part numbers for repair terminals. Here's an example of what that looks like (looking up a different connector though). The part number visible in the example is for the plastic housing; you have to click the '+ Wire Harness Repair' underneath it to see the numbers for the terminals.

When you get a repair terminal from the dealer, it will have a short length of wire preattached. That lets you cut out the old corroded terminal and the wire a little way back to good copper, splice the repair terminal on, and click it into the housing. If the plastic housing isn't deformed or melted, cleans up ok, and the terminals click securely into it, there shouldn't be any need to replace it. The harness repair page will also show the recommended crimp sleeve for making the splice. (Also, it shows how the terminals are locked in place and released. Worth studying; there is usually a primary 'lance' that is either part of the terminal or of the housing—the diagram will say which—and a secondary lock that is part of the housing. Both need to be released to get a terminal out.)

That would give you the repair up to Toyota's specs. Alternatively, you could follow TMR-JWAP and just splice around the whole connector, though that could end up being annoying if you later do have some reason to want to disassemble it.

 

TIS is the technical info servive, the online resource at techinfo.toyota.com. It's subscription-based, but the (more info) link I gave also has information Elektroingenieur compiled helplfully about getting access through local libraries, etc. (I trust, in the current situation, there are ways of accessing the local library online....)

All of the repair manuals are there, wiring diagrams, service bulletins, campaigns and recalls, quick technical guides, even the "University of Toyota" technician course materials. Just the one subscription covers all of it.

 

+1
That is the connector I was referring to. Just get some wire nuts and splice around the bad spots.
Again, It's an old car.

 

Start with one wire with a corroded pin. Cut the wire on both sides of the connector, strip them, and then connect them with a wire nut. There is no need to trace anything back. Your pictures show just two bad pins. This will not make the fan run constantly.

 

You're right, imgur is being stupid, so I don't see the splices you used.

These are the good stuff, as spec'd by Toyota:



They are parallel splices: the two stripped ends of your wires overlap in the middle, and you crimp down the barrel to smash both stripped copper ends together, and the current is carried right from one wire to the other.

Auto parts stores for some reason more commonly sell butt splices. You can recognize them because their middles are narrower than the ends, and longer than the middles of the parallel splices:



They look similar, but your two wire ends don't end up overlapping. There's a stop in the middle. One wire goes in one end and stops, one goes in the other end and stops, and you crimp both places, and the current has to flow through the splice barrel.

And then there are these kinds of things, that only conduct through one little blade that mashes down through the wire insulation:



Those are really not the ticket. But if you used one, and it worked, I would probably call it a day, and if it flakes out later, just replace with a better splice. Maybe it never will.