Prado w/ “premium sound option”: 14-pin factory stereo plug (KZJ78 and KZJ71 plus LJ78 and LJ71)

[kgrove]

Background:

I just completed the head unit (HU) replacement for a KZJ78 Prado and thought I would write this one up as it had a factory audio configuration that is rare and poorly documented. Rather than the standard dual factory plugs behind the dash I'm used to, this one had a single, 14-pin factory stereo connection. I know from other threads this could apply to the LJ and KZJ Prados, but I found no mention of the same setup on any other 70 series. The only other use of the 14-pin connector that I can find is from a 1991 Toyota MR2 with the premium sound option. That MR2 variant was likewise driving their owners crazy trying to find a stereo harness for it, but luckily for us, MR2 owners appear to be further out on the audiophile spectrum than LC owners, so I was able to find a solution there. There was at one time an aftermarket stereo harness made by a British company, the Autoleads PC9-406, but it appears to be unavailable now.

From what I can piece together, 70 series Prados (both the LJ and KZJ families) came with either standard sound (substantial / overwhelming majority of units) or a “premium” sound package (somewhat rare) and the two variants have different factory stereo connectors behind the dash. Standard sound cars have two factory plugs behind the dash and rely on the HU’s internal amplifier and a HU replacement is easily done with the Metra 70-1761 harness. That's well documented and I won't discuss it here. Premium sound option cars have a single 14-pin connector used to send signals to a pair of amplifiers behind the left rear side panel (one above the tool kit and one under the speaker). There is no harness available to tackle the 14-pin stereo connector and documentation is poor. There are a couple threads around here that mention the 14-pin plug, but none were successful at producing a wiring diagram and most basically concluded the easiest solution was to abandon the plug and rewire at least for speakers.

Here’s what the 14-pin connector looks like after disconnecting your factory (or aftermarket) HU:

Here are the rear amps - one above the tool pouch and one below the speaker (for information only - you don’t need to access these to replace your HU).

Possible Solutions:

There are two broad solutions to replace the HU on a premium sound Prado with the 14-pin connector:

1. Rewire: Run new speaker wires to your new HU or a new amp and tap other sources for battery, accessory, etc leads
2. Build a 14-pin harness: Use the male side of the 14-pin connector used by the HU you are removing plus a couple RCA plugs to build a 14-pin harness for your new HU

#2 is the easiest HU swap and it’s what I’ll document here, but it does assume the 30 yr old factory amps are still adequate for your needs. It also assumes the HU you are installing has RCA outputs.

I should mention one of the other threads mentioned that there should be both sets of plugs present, but the dual plugs are buried. In other words, it suggested all Prados deliver with both the dual plug and single 14-pin plug available, but only one set is utilized and the other set is tucked away. While I did not tear apart the dash to disprove this, I looked everywhere I could reasonably access and could not find the dual plugs hidden anywhere. Either that other mention was wrong or the dual plugs are VERY well hidden. I also do not recall seeing an unused 14-pin plug in other Prados unless they do a very good job of hiding it somewhere.

Parts Required:

• RCA plugs with bare pig tails. I bought 4 of these on Amazon for about $20 for the pair. You could probably cut the ends of an unused set of RCA cables, but sometimes the wires on those are very fine and difficult to work with, so I bought these. Amazon.com - https://www.amazon.com/gp/product/B081TYCKC6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
• The male side of the 14-pin connector from your factory HU with long enough wires to allow for connections to your HU harness

If you are going to cut the RCA plugs off an old AV cable instead of buy them like I did, the center pin of the plug is the positive and the ring around the pin is the negative. You can do a quick continuity test to verify with wire is which since many cables aren't labeled (my purchased ones were coded red and black).

Wiring Diagram for the factory 14-pin plug:

Here's the wiring diagram for the 14-pin connector that I found on an MR2 site, but it does include some notes that don't apply here. I don't think the color codes match up with Prado, so you'll have to pay attention to the connections on your old stereo or do some testing to orient yourself and ensure you're reading the diagram correctly. The column about "alternative sources" was only relevant to the guy that wrote this... I think they were installing a new amp and were only using the factory plug to grab common leads like battery and accessory power, not audio. The notes also reference the "BGB"... had to look that one up as I hadn't hear it. It's the "big green book", which I assume is what MR2 owners call what we here call the FSM or EWD (field service manual or electrical wiring diagram for those visiting the site like I was the MR2 site).

New Harness:

Cut the male side of the connector with enough wire as a pig tail to work with comfortably - anywhere from 2-4". The male side will look like this:

The wires from your HU pig tails will be connected to the male 14-pin connector like this to make your "Metra like" stereo harness (stereo pigtail lead --> 14-pin connector position):

Control and power:

• Amp --> pin 1
• Illumination --> you'll need to test this as pin 2 and pin 8 are listed as + and - for illumination. I don't recall how I connected mine
• battery --> pin 3
• Accessory / switched power --> pin 9
• ground (main) --> pin 10

Audio (RCA connectors --> 14-pin connector):

• Front Left positive --> pin 5
• Front Right postiive --> pin 6
• Rear Left postive --> pin 13
• Rear Right Positive --> pin 14
• FL, FR, RL, RR negatives --> pin 11

It's this last one - connecting the negative leads from all 4 audio channels to the shared negative pin 11 - that I think tripped everyone up who was trying to reverse engineer the wiring diagram. Here's what it looks like - the four positives / red leads from the RCA plugs connecting to their designated pin, then all four negatives joined to the shared audio ground pin #11 (under the blue shrink wrap). The key for this to make sense is unlike the standard setup (HU sending speaker level outputs directly to the speakers through a separate positive and negative wire per speaker), this is sending low level outputs to the amps in the rear. To do this it only needs 5 wires - one positive per audio channel plus a dedicated audio ground to serve as a common negative.

Separately and depending on your HU, you may need to tap leads for reverse and parking brake signals as they are not in the factory connector. My HU only requires grounding to override the parking brake signal, but I've done an Alpine on a different car that needed a parking brake overrride module (I think it sends a pulsed on-off-on signal rather than using a direct to ground for a constant signal). Reverse would only be needed if you are connecting a backup camera.

Once you have this harness built, it will behave exactly like a standard HU swap.

Caveats:

• Sorry about the illumination confusion... you'll have to test those two illumination sources and see what works. It's been about a month since I did mine and I don't recall how I connected it. You could test the truck side of the 14-pin connector with a multimeter to see which pin is giving a voltage when the lights are turned on.
• I have some confusion on the amp and power antenna pins (#1 and #7) but could not test them as my power antenna motor isn't working. There's a note in the MR2 derived wiring diagram about connecting the antenna lead from your HU to both the amp and antenna pins on the car side. I don't know if that footnote is correct or if it applies to the Prado as well as the MR2.

I hope this helps somebody. Please post any corrections or improvements you see for this.

 

[CFMCPA]

While you were in there did you add back-up camera? I did recently and mounted the camera in the license plate light housing in the rear. Finding that it is just enough offset and limited angle to be of much use - was thinking about shifting it up to the roof brakelight bar. Curious if you've found a better location. Also going to find a better camera, perhaps fisheye would help.

Awesome write-up above - thanks for taking the time.

 

[kgrove]

While you were in there did you add back-up camera? I did recently and mounted the camera in the license plate light housing in the rear. Finding that it is just enough offset and limited angle to be of much use - was thinking about shifting it up to the roof brakelight bar. Curious if you've found a better location. Also going to find a better camera, perhaps fisheye would help.

Awesome write-up above - thanks for taking the time.

There was already a backup camera in place from the prior owner, so I didn’t have to go to the hassle of running the wires to the back. But yes, the camera is mounted in the license plate light housing. I find it works adequately, certainly for normal driving. I haven’t towed, so no idea how helpful it would be at aligning to a trailer, but I’m sure inferior to a central mounted camera. Check whether the spare tire would block important angles before you mount on the brake light. I’m guessing it would be great for parking lots etc, but possible the tire blocks stuff on that side of the car as it gets near the car - precisely when you’d want to see.

 

[CFMCPA]

Thanks for advice! Under license plate decent for trailer; spare probably about the same but worth a shot. Will jot down what I find in new thread, thanks again!

 

[erkl8872]

My Prado had this 14-pin as well, but luckily I had the adapter already installed on my ancient aftermarket head unit when I went to replace it. But I found this mr2 site where you can order an adapter from UK. Looks like it's just someone making them and selling. Stereo Harness Lead RCA to ISO Toyota MR2 mk2 (with active speakers.) - https://mr2-ben.co.uk/products/111