What is in the 20-pin radio harness?

Permit me to suggest techinfo.toyota.com, where you can find 2 very interesting things:

• The New Car Features manual, with its section on the car's communication networks, which will explain to you exactly what's going on with the 68-ohm resistor business, etc.
• The Electrical Wiring Diagram, which will tell you all about exactly what's in that 20-pin connector, what color and which pin (not to mention part numbers for the connectors and pins, should you need any of those).

-Chap

 

@ChapmanF makes a good suggestion. Besides the two references he mentions, also see the Repair Manual, under Audio/Visual: Audio Visual System and Navigation: Navigation System. Each of these sections has Terminals of ECU pages, with descriptions of the signals present on each terminal, and Circuit pages that explain some of the circuits and signals in more detail.

 

Download the car service manual pertaining to the electronics in the car. It is a wealth of good info about what is there, and if you read prints as well as I do, it becomes a roadmap to fun!!

 

From the notation you mentioned, you’re probably looking at the “Multi–Display and Audio System with Built–in Amplifier” pages in the System Circuit chapter of the Electrical Wiring Diagram, which Toyota publishes as a separate book from the Repair Manual.

“R 3(A), R 4(B), R 5(C)” means there are terminals of three connectors shown in that depiction of the Radio and Player, and the terminals labeled there with symbol Ⓐ are on connector R3; with Ⓑ, on R4; and with Ⓒ, on R5. For example, the GND terminal on the Radio and Player is labeled 7 Ⓐ. This means it is terminal number 7 of the connector with symbol Ⓐ, that is, terminal 7 of connector R3, sometimes abbreviated as R3-7.

The letter designations are arbitrary. For example, when we meet the Radio and Player again on the ”Multiplex Communication System – AVC–LAN Bus” pages, it’s labeled “R 5(B), R 6(A).” This doesn’t mean there is anything different about connectors R5 or R6, only that to explain the multiplex system’s wiring, there was no need to show any terminals from connector R3, so no letter symbol was allocated for it there.

The System Circuit pages sometimes show terminals from the same connector on different pages, if the terminals are used in different systems. The same terminal can also be shown on more than one page, if it’s used in more than one system.

The shape and terminal numbering of each connector are shown in the Connector List chapter of the Electrical Wiring Diagram. There we see that connector R3, for example, is a 10-position connector. The Electrical Wiring Routing chapter shows where to find each connector on the car; R3, R4, and R5 are all shown on the Position of Parts in Instrument Panel pages.

The letters in the connector designations also tell you the general area of the car where the connector is found; “R” means the center of the instrument panel, for example, not a class designation for a resistor.

Many connectors are also shown in the Repair Manual proper, in the Terminals of ECU pages for each system. These pages have tables explaining how terminals are used. For example, under Audio and Visual System, the table includes this entry for the GND terminal:

Symbols (Terminal No.): GND (R3-7) - Body ground
Wiring Color: BR - Body ground
Terminal Description: Ground
Condition: Always
Specified Condition: Below 1 Ω​

The Repair Manual also includes circuit troubleshooting information. For example, the Radio Receiver Power Source Circuit pages show connector R3 in the second step of an Inspection Procedure, in which the voltage between the supply and ground terminals is checked.

Note the hint “*1: for 6 speaker system,” which means that the information shown with the note symbol “*1” applies only if the car has the six-speaker sound system. Notes like these appear often in the documentation for systems that vary depending on the car’s grade (trim level) or factory-installed options.

 

I wanted to pitch in the fact that without the factory radio installed and without that resistor, it's not just the HVAC that doesn't display. The MFD doesn't display outdoor temp, status of hybrid drive, or average MPG. The screens are there, they just are blank. I know this because I yanked my factory deck today, and am trying to find a 68 ohm resistor. Man, do I miss Radio Shack.

 

Interestingly enough, after I hooked up the resistor to the harness, it showed the MPG accrued on that tank. In other words, all the calculations are still performed, you just won't see it until you get that resistor installed.

 

I know this is an old post. Hoping to gain some answers. I'm upgrading to an aftermarket radio in my 2009 Prius. I have the 86120-47200 radio, has an empty aux input but other 3 harnesses are used. I know what 2 of the harnesses do and how to connect them, but the 20 pin remains puzzling. I'm good with pins 6-10 and how to hook them up. But my harness has alot more wires and I don't know what to do with them. I still have these pins...

1 - Black
2 - White
3 - Purple
15 - Green
16 - Gray
17 - Red
19 - White

Could they just be extra and unused in this harness?

2 photos attached. Thanks for any help!