Please help! Wiring issue.

Where did the damaged wire harness plug into? I am guessing the pictured harness belongs to the big silver canister, the CHRS (Coolant Heat Recovers System). Since the car is reporting a "cooling" DTC (Diagnostic Trouble Code), I infer the code points to that harness that likely belongs to the CHRS. Since the car is not reporting ABS codes, I will assume no damage to the wheel sensor.

If, that harness belongs to the CHRS, just repair the damaged wires (via splicing in new wire of same gauge), OR cut off the CHRS wire harness from a donor junk yard vehicle and solder into yours, OR contact Prius hybrids sales and service Scottsburg Indiana for a 1-2ft length of that harness.

 

I would just cut off a small section of damaged wire off, that has a small section of UNDAMAGED wire attached. This undamaged section will act as your wire gauge determiner. I would have to guess 20-22Ga wire? You can always replace the damaged section w/ a thicker wire (smaller gauge number), but don't replace w/ a thinner wire.

By repair, this means cut off damaged sections and SOLDER new wire of same gauge and length, to keep everything as close to original as possible. Best to use heat shrink tubing to seal the soldered sections. DO NOT use wire nuts, butt, or cap crimpers, as the wires will likely work themselves loose over time due to vibration from the engine and suspension/road.

 

For a different recommended technique, Toyota's own wire harness repair manuals and training always specify crimp sleeves (properly crimped!) as opposed to solder.

Toyota sells 'repair terminals' which are the proper connector pin or socket pre-crimped by the factory to a short length of the correct gauge wire, which should be long enough (or so one hopes) to reach back to an undamaged spot on the original wire and splice there. The wiring diagram viewer lets you click to expand the "wire harness repair" section in the drawing of each connector, and it will tell you the part number of the repair terminal, the gauge of the wire, and what crimp sleeve and heat shrink to use.

For connections that are outside the car, the specified heat shrink tubing will be a sort that also exudes a sealant when you heat and shrink it.

The tool for making up a crimped connection properly will not be the thing you see at the hardware store with a tooth that pokes the barrel in one spot. The good ones are more expensive than that, but @Elektroingenieur has posted about where to get them for prices better than Toyota's.

Using solder by itself is generally frowned upon in auto and marine electrical systems; the American Boat and Yacht Council specifically bans it. A big part of the issue is the solder wicking some distance along the strands of the wire, turning it from flexible, stranded, vibration-resistant wire into a brittle stick.

It is permitted to go belt-and-suspenders with a crimped connection and then solder (not the other way around!) but it's not clear that any better connection really results.

-Chap