Quick Info:

2003 4Runner Limited V6

Installed years ago: Pioneer SPH-DA120

Recently installed a Garmin dash cam with the parking mode cable (used fuse taps into driver power seat for battery power and the ACC fuse for on power).

I also recently had problems with my air condition status light blinking and the AC not working. Searched around and found a post saying it was a common problem, replaced the relay and it's beed good ever since.


Problem of the day:
A problem i've always had after the aftermarket radio was installed was that FM radio reception became horrible. Wasn't a huge deal since I usually use my phone, but I did some searching and found a forum about using and adapter and splitter to bring the AM and FM antennas together and then plugging into the aftermarket radio, as well as making sure the amplifier has power to it.

Took everything apart, connected the two antennas and then plugged them into the radio... powered it up to test if there was any difference (there wasn't really), but before i could really get any farther than changing the station a couple times the radio just suddenly shut off. Turned the car off and back on and it still doesn't power on. Weird.

Must be a fuse right? Used my multimeter to check both 20amp fuses under the hood, they're good. Checked the 10amp on the back of the radio, also good. Checked to see if the harness has power... no go. Weird. Check the 12v outlet plug next to the gear shift and find it also doesn't have power. Extra weird. So then I go and check the ACC fuse under the dash (where I have it fuse tapped for my dash cam, which still has power and is working fine), and the ACC fuse is blown. I'm not sure how that could have blown when I was working on the radio, but hey, I barely know what I'm messing around with.

Replace that fuse and plug it back in still using the fuse tap. Excellent, now the 12v outlet and the factory radio harness both have power again. Plug in the aftermarket harness and the radio still doesn't power up. What the hell? I then use my multimeter to check the continuity of every wire from the pins on the factory side of the aftermarket harness to the connector on the radio side. They're all checking out fine. In the process I find a purple wire that had been partially cut somehow, even tho continuity on it still checked out. Respliced the connection and double checked continuity was still there, good to go. Checked the radio again, still nothing.

So now I'm starting to wonder if the aftermarket radio is dead. Okay, fine. Go find the old factory radio and try plugging it in to the factory harness. Nada. Double check the factory harness still has power, which it does. Take out my fuse tap in the ACC spot and put in a brand new fuse, still no joy.

I'm at my wits end here guys. I've done the troubleshooting that my amateur level of knowledge has allowed me to do. I'm hoping that this is some simple fix that i'm just overlooking, but I have no idea what it could be. I've tried doing some searching, but mostly just come up with replacing the ACC or back of the radio fuses and I've already done that. I truly don't understand how just using a Y to connect the AM/FM antennas could have caused this mess.

Any advice or help anyone can give would be greatly appreciated!

EDIT 1: Oh, I also pulled every fuse and checked for continuity, they're all good.

Definitely an interesting one you have there.
Try taking the red wire loose from the radio harness and touch it to the yellow wire and see if it comes on.
Yellow is constant power
Red is switched power.
If it comes on then there is a problem with switched power.

So using the wiring diagram in my link below I’m testing the C and D spots with using G as my ground. C is ignition (switched?) and D is Battery. C shows 12V when the engine is running, D isn’t showing power regardless of if the engine is running or not. C is a light grey wire, D is blue with yellow stripe. The only yellow wire I found on the factory side of things seems to be a speaker wire? I’m not sure. It’s not on the main connection for the radio however, it’s a separate plug.

Imgur: The magic of the Internet

So wire D is definitely your problem. That’s the wire that supplies power to the radio.
C just tells the radio when to turn On and off.

Double check three fuses. Radio/OBD/power outlet or cig lighter. If those are all good you will need to trace wire D back and it might be broken somewhere. You could always run a new constant power wire as a replacement for wire D if you want to. It would go to yellow on the radio harness.

I’m willing to bet if you take the red wire and yellow wire from the radios harness not the cars harness and put them both on wire C the radio will turn on when you turn the key. Although this would work you would always loose your settings and radio stations without wire D to keep memory.

That makes a lot of sense! Though I can't imagine why that wire would have lost power just because I pulled the radio out to mess around with the antenna wires. I didn't pull very hard on the harnesses or anything. Who knows. I'll have to work on it some more tomorrow. Thanks!

Alright, made some progress this morning. Ran a 20amp fused wire directly from the battery and jammed it directly into the back that D spot, and low and behold, it works again! So that’s definitely the problem like you said. I tried testing continuity from the fuse box to the end of the factory harness. Radio fuse 1 has continuity to the switches power in C, so I figured radio fuse 2 is for the D spot? But I can’t get continuity from the right side of the fuse to the end of the wire, which I think confirms that wire is broken.

Long story short, I used a fuse tap into this radio number 2 spot to run a new wire thru the firewall and cut the blue yellow wire that’s in the D spot and connected it up. Should serve as a permanent replacement for that blue/yellow wire. Thanks a ton for your help!

As a side note, any thoughts on why my radio reception is still bad? I used the Y connector I bought to bring the AM/FM antennas together and I verified the third wire in the antenna bundle has power, which should be for the amplifier? I’m honestly at a point where I’m probably not going to mess with it too much now since I’m just glad to have the radio powering back on, but if I’m overlooking something easy to fix then so might as well while I have it all torn apart.

Thanks again!

Glad it’s working!
Definitely weird that the reception is still bad. Mine is only using the larger plug and works fine.

Go ahead and change that 20 amp fuse for a 10. That’s all you need for the radio and will protect the wire better.