Introduction

The Toyota Prius has a control bus for the AV Lan called the IEBus. The audio/video components communicate with the Multi-Function Display via this control bus. When adding a CD player or changer to the Prius, you must purchase Toyota's "CD Setting Kit" which consists of a couple of mounting brackets, a grounding strap, and a complex Y-cable. The Y-cable goes in between the radio and it's normal R4 connector, and splits off an identical set of signals for the CD player. The signals carried on the cable comprise the IEBus control signals (TX+, TX-), audio R/L +/-, audio mute (active low), battery, ignition, and grounds.

While I had the dashboard partially apart to install my Samsung SCH6100 phone hands-free kit, I wanted to put in the Y-cable so I could have a handy accessible IEBus port for sniffing communication, and I wanted the extra R4 socket in place for when I get my MiniDisc Changer (hopefully!) from Japan. (It's waiting on electronic compatibility verification from a Tokyo dealer.)

Besides, I needed to tap the "audio mute" signal for the Samsung handsfree kit to silence the radio when a call comes through. I did this in my Acura with a Pioneer radio and it was very convenient. So when I got the Prius, I got another Samsung handsfree kit and wired it up the same way.

The Y-Cable

Here is the Toyota Y-cable from the "CD Setting Kit" with my modifications. Notice the two new Molex connectors on the lower right. These are my six-pin IEBus connector (bottom), and single-pin audio mute connector above it and to the right with the blue wire.

The plug part of the "Y" (left, top) goes into the Prius in-dash radio. The socket part of the "Y" (left, bottom) gets plugged into the R4 plug that you remove from the radio.

The socket part to the right is the new connector for the CD player or changer (and hopefully for my MiniDisc player).

My add-on cables come from the lower-left socket part where it first comes from the Multi-Function Display (MFD). The following paragraphs detail how the splices were made.

Click here or on the picture for a hi-res view.

Splicing the Wires

Notice on the top row, third pin from the right, there are two black wires going into the same hole. I made the splices by soldering the new wires right on the metal pins. The connector housing has plenty of room where the pins go in to accommodate the extra wire. This was a very convenient way to do the modification. It is minimally invasive because it does not require the cutting of any wires. The green and white wires are branching upward because the pin is removed for photography. See the following pictures.

Soldering Details

The images below show a green wire soldered onto the pin that previously hosted just the white wire. The pins are finished with a plating that takes the solder very easily. The right-hand picture shows the wires separated so you can see the two of them distinctly. I tinned the connector and the wire, and then sweated them together. Once together, I held the wires together and flowed some fresh solder to avoid cold joints that could later break in the car with temperature shifts and vibration.

Molex Connectors

The picture to the left shows the details of my new molex connectors. The lower connector is the 6-pin IEBus connector which also contains battery, ignition, and ground for maxiumu flexibility. The upper connector is the single-pin audio mute.

Notice that I used the socket-side (female) of the molex plug/socket pairs because the pins are recessed and less likely to short out to anything behind the dash while dangling there.

Just a note about the audio connector: The fragment of the radio schematic I received from Harry Eaton showed a diode inside the radio facing with its cathode toward the audio mute pin. Judging by this, I concluded that the audio mute function worked by grounding the pin. I was correct. It worked perfectly with my Samsung handsfree kit.

Modification Cable Pin Connections

Here is the pin detail of my modified cable with the complete pinout of the Toyota radio R4 connector with signals and colors labelled, along with my new cables showing the points of connection.

R4 Pin #	R4 Signal	R4 Color	IEBus Pin #	IEBus Color	Mute Pin #	Mute Color	Notes
1	R+	VIO
2	L+	PNK
3	S-GND	BRN
4	MUTE	YEL			1	BLU	For cell phone
5	BU+B	YEL	1	RED			Battery
6	R-	BLU
7	L-	GRN
8	GND	BLK	3	BLK			Gnd
9	TX-	GRY	5	BLU			IEBus Data
10	TX+	WHT	4	BRN			IEBus Data
11	/EJECT	GRY
12	ACC+B	RED	2	YEL			Ignition

Copyright © 2002 John R. Haggis. All Rights Reserved.
Last updated: 5/23/2002