Identifying and splicing wires

Unlike days of the old 12 volt system, a lot of circuits have 5 volt ECU's.

I would not "cut and splice" circuits in a modern car.

I had to wire in a 3-2 trailer taillight converter. I did not cut and splice any of the wires. I used insulation displacement tap connectors. The wires are of a very small 22 gauge, so one must be very careful.

If I need a new circuit, I'd wire it directly to the fuse box.

It could be very costly, if you do not do your own work and expect someone who don't know what you did to the wiring, as it might take many hours to troubleshoot.

Cutting and splicing wiring might void the factory warranty.

 

According to Prius Gen 3 manual, in the ciggaretes power outlet you have only 2 wires, Black and white-black.
You can connect your gear to the black wire, it have 12 V+

 

There's an easy answer to that part. The Electrical Wiring Diagram manual, part of Toyota's published repair info for the car. PriusChat has this wiki page that was kindly compiled by Elektroingenieur with information both on getting it directly from Toyota's sites and from other services like libraries where it may be conveniently available.

As for tapping into the wiring, there are various approaches, depending on how interested you are in being able to return the car to stock.

I often identify the circuit I want near one of the wiring connectors in the car. The wiring diagram will show the wire color and which terminal of the connector it is, how the terminals are removed from the connector, and what the part number is for replacement terminals of the same style. Sometimes I'll remove the original terminal from the connector, add a repair terminal in its place, and join the two in a little Euro-style terminal block with the original terminal pushed all the way in, but the screw only clamped on the crimped part (careful not to mash down the shaped part of the terminal). That makes a complete return to stock possible.



Cutting and splicing with the correct size parallel crimp sleeves and insulating with heat-shrink tubing (the sealant-lined kind, if the splice is outside the cabin) or silicone self-bonding tape is what Toyota would specify for a secure permanent connection able to carry full current. Elektroingenieur also put together an informative post about that.

While insulation-displacement connectors are certainly easy to use, I think that's about all that can be said for them in a car environment. They still pierce the insulation; it's not as if they somehow avoid compromising the original wiring. They connect to the wire inside by pinching it in slots in thin blades. That can work quite well on solid-copper wiring (telephone wiring closets are full of the things), but car wiring is made of many very thin strands. The blade of an IDC connector may end up actually cutting right through a few of the outer strands, and then sort of draping loosely over the inner ones.

Bringing a new circuit right from the fuse box is often an option. There are sometimes even unused fuse slots in it. The wiring diagram will show which supply feeds each slot (always on? ACC? IG ON?) and which unused terminal(s) of the junction-block connector the fused circuit emerges on (and the part number of the terminals used in that connector).

 

I used them only for low draw signaling circuits like turn signal powered trailer wiring adapters. For high draw, I'd either solder the connection or add a new circuit directly to the fuse block.

 

Soldering is another technique many people swear by and use everywhere. Toyota (and other car/marine/aerospace makers generally) reserve it for completely rigid, fixed connections (like components on circuit boards inside ECUs), but make very specific recommendations about crimp materials and tooling when they are talking about joining flexible stranded wires in harnesses, where solder can wick along the strands and make stuff brittle.

 

It depends on your technique. For butt splices, I use a stiff clear marine grade heat shrink tubing that makes a stiff support for the connection. The clear heat shrink allows visual examination of the connection as it ages. Unfortunately, many load the connection with too much solder. More is not better!

In the case of a "T" splice, I used a scrap "tail" of a nylon zip tie to support the splice when taping it. The vibration and flexing is limited to the flexible stranded portion of the wiring.

 

It is not my aim to personally evaluate anybody else's preferred technique, but only to convey what the manufacturer does and doesn't recommend and why.

 

The manufacturer, as many instructions are written, are for the lowest skilled and least skilled individual. I recalled that Ring doorbells were recalled, because home installers used the pointed head screws supplied for mounting into wood to secure the battery cover and drove them into the lithium ion battery and cause a fire.

 

Maybe this will help.

Toyota Prius (XW30) (2009-2015) Fuse Diagram • FuseCheck.com

 

When contemplating adding a new circuit, it's generally worth going straight to the real electrical wiring diagram (more info). There you'll find the internal connection diagrams of the fuse boxes, several pages in this vein:



You can see there's a spare fuse position derived from the IG1 no. 3 relay (so it would only have power with IG on) and coming out on connector 2A position 15. Then you can see several spare fuse positions that are always powered. One of them comes out only on 2A position 12. One of them feeds 2B position 24 and 2D position 15. And so on.

So if you just buy a repair terminal of the type used in (for example) connector 2A (part numbers are in the online EWD), attach it to your new circuit, click it into position 15 of that connector, and add a fuse in the empty slot, you're in business.

Image copied from this earlier post where there are more details.

 

You can use CTRL and + for zoom in the browser...

 

I posted just one small excerpt of what's in the Electrical Wiring Diagram manual (more info).

In addition to the rest of the fuse-box diagram, the EWD has the Toyota part numbers for the repair-wire terminals that are used in each connector in the car. For example, if there's a circuit you want to use that comes out on somepin of connector 2C or 2D, say, you can find those connectors and get the part number of the repair wire to use. This post has an example of how you find that.

Specifically for connector 2C (if you've found a circuit that comes out there), the two terminal part numbers are in this post I linked to earlier. The connector uses two different sizes of terminal, so you just have to look at the drawing and find the number of the pin you're looking at to see whether it's one of the bigger or smaller ones.

A hint: on that junction block, connectors 2C and 2D face the driver and are easy to reach; 2A and 2B face the firewall and aren't.