I owe this thread an update, just in case anyone else is (for some silly reason) interested in putting a stock head unit back into their 80 like I was.
To reiterate, my HDJ81 had an aftermarket head unit with Japanese writing I couldn't change to english, and wouldn't pick up US radio stations. I found a US head unit off of a wrecked '95 via B&R Autowrecking's website. They shipped it right to my door for ~$45 all in, which is a steal compared to what units are going for on Ebay.
When I pulled the aftermarket unit, as expected, it was using the grey harness Toyota included for this purpose. However, the stock white wire harness that should have matched the US stock head unit did not match it. I'm not sure if some Japanese-spec cruisers had a different plug or perhaps a different stock head unit than the US. What was strange is that the amp-side of the harness in my truck did indeed match the stock US head unit, which tells me someone re-pinned the white head-unit side at some point.
Old junk. What a mess. All the Japanese toll sensors, wires, and antennae filled a small bin up once pulled out.
What I found after pulling all the aftermarket wiring junk out. Note the white plug is the plug of concern that should match the stock head unit, but did not.
Plug I needed on the back of the US head unit
My first thought was to get the stock wire harness cut out of the wrecked '95 I got the head unit from. B&R no longer had the harness- they pull sellable parts and crush the rest of the car :/
My ultimate solution was using
this harness catalog in conjunction with pulling the part# from my preamp harness to ID the exact plastic wire harness I needed to re-pin to.
I checked for NOS harnesses (plastic plug only) and they are NLA. No luck on Ebay, partsouq, toyotapartsdeal, etc etc.
So I started scouring Mud for 80's being parted out and did some mass outreach asking for just the head unit plug. I finally got a hit and the Mud member sent me two of them, the head unit side and the amp side (again, same exact plug).
I had him clip the wires so that I had a reference as to how to correctly re-pin the wires on my harness to match up with the stock US head unit.
One by one, I released the wire pins from the harness in my HDJ and placed them in their correct slot on the stock harness. The Japanese pins ARE NOT exact matches to the US pins, so I had to do some slight pinching and bending with some needle nose pliers to get them to fit the US harness.
Once that was all done, I re-plugged in the amp harnesses, which were bypassed for the aftermarket head unit to work. I plugged in the silver radio cable into the stock head unit, and plugged in the freshly re-pinned harness.
The unit works, albeit the CD player reader rails probably need to be re-lubed as only 1/10 CDs will actually play. This is a well documented issue with old head units. Tapes play well. Radio now picks up US frequencies. All of the 9 stock speakers now work as well (aftermarket head units only utilize the door speakers when you bypass the amp).
I've done about 30 hours of road tripping with the stock head unit in now and it's been a joy to listen back through my parent's old tape collection.
Anyway, that was a PIA and I will eventually put an Android carplay unit in and install all new high end speakers + sub at some point. But for now, having the stock unit work has been a lot of fun. Surprising how good it actually sounds for a 27 year old truck.
Hope this helps some other 80-owner looking to go back to stock with their radio! As always, huge thanks to the folks on Mud for being such a good reference in such projects.