Bet this will stump everyone!!!! voltage disappears when head unit plugged in.


2004tundra

CarAudio.com Newbie
Apr 7, 2021
8
0
texas
So I have a 2004 toyota tundra SR5 4x4 4.7L. It had the stock head unit in it which consisted of a CD player and cassette deck in a single, double din head unit. Since I'm not really a big car audio enthusiast and this is my work truck, I never changed it out. I decided to buy one of those Chinese "Konifo" double din head units from amazon https://www.amazon.com/dp/B08V1HJKB8/?tag=caraudiocom-20 . When I hook it directly to a 12v battery, it powers up right away, so I know it works. I have the service manual for this model truck so I have the wiring diagrams. In the stereo wiring from the truck there is only one ACC wire and one constant 12V wire. Radio ground wire is the brown wire. Hooking the volt meter to the constant 12v wire reads 11.6v with the engine off and 12.65v when running. The ACC wire reads 0 volts with key in off position , 11.6v with key in ACC position and 12.65v when running (with the black lead of the volt meter on the brown ground wire) Connect the head unit and the voltage disappears completely from the ACC wire and drops to 1.9volts on the constant voltage wire. Is it possible the truck's computer senses something other than the factory head unit and kills the voltage to these wires? I have never read about another 04 Tundra doing this. I checked this again and again, unplug the harness from the head unit, insert probes into the harness, back up to normal voltage, plug the unit unit back in, voltage disappears, unplug and connect directly to 12v battery and it powers right up again. Has anyone experienced this? I think if I ask anyone , they wont believe its really doing this, it doesn't even seem scientifically possible.
 

Popwarhomie

CarAudio.com Elite VIP
5,000+ posts
10+ year member
Jan 22, 2010
9,337
1,795
FL
Try using a different ground. If you have some spare wire just run it from the battery negative into the truck(temporarily) and use that ground. Does it still do the same thing?

Should have higher than 12.6 volts while running.
 

2004tundra

CarAudio.com Newbie
Apr 7, 2021
8
0
texas
  • Thread Starter Thread Starter
  • #3
Hi, yes, I suspected maybe a bad ground so (Temporarily) ran a wire directly to the negative battery post, no change in behavior. My next try was to run a constant 12v wire to see if that would power it on. But really shouldnt have to do that. The old head unit was working fine when I removed it.
 

Popwarhomie

CarAudio.com Elite VIP
5,000+ posts
10+ year member
Jan 22, 2010
9,337
1,795
FL
I wonder if that ching chong wiring harness is the issue. Pins not having a good connection or something.
 

2004tundra

CarAudio.com Newbie
Apr 7, 2021
8
0
texas
  • Thread Starter Thread Starter
  • #5
lol, maybe but it works fine hooked directly to a 12v battery through the harness, and I actually have 2 at the moment since I told amazon it didnt work and they sent a replacement, both head units work when directly connected to the battery. (connecting both red &yellow wires from the harness to the positive terminal and the black wire to the negative terminal)
 

audiobaun

CarAudio.com Veteran
5,000+ posts
Jun 28, 2011
10,705
299
USA
Sounds like it could possibly be a ground issue through the harness. Might check your wiring connections to also make sure they are tight and not loose . Find a shorter grounding location as well. Your voltage sitting sure seems low also.How old is your battery and how old is your alternator?
 

audiobaun

CarAudio.com Veteran
5,000+ posts
Jun 28, 2011
10,705
299
USA
Its possible that the new HU could have gotten moisture internally as a unit that may have been sitting in a warehouse for quite some time as well before sale or shipping? Something to be considered
 

1aespinoza

Junior Member
May 22, 2013
847
229
Pharr, Texas
lol, maybe but it works fine hooked directly to a 12v battery through the harness, and I actually have 2 at the moment since I told amazon it didnt work and they sent a replacement, both head units work when directly connected to the battery. (connecting both red &yellow wires from the harness to the positive terminal and the black wire to the negative terminal)
Connect both positives to the constant on the harness. If it still drops, check the oem fuse size. Check the manual for recomnended fuse as well.
 

2004tundra

CarAudio.com Newbie
Apr 7, 2021
8
0
texas
  • Thread Starter Thread Starter
  • #11
If that doesn't work try a fuse tap for a different power source
Thanks for all the advice, someone asked earlier about the truck battery, It's new, well, bought it in January. Toyota used a "blue with yellow stripe" for the constant 12v memory wire. It reads 11.6v (not running) and 12.65v when running. Im going to try running a new ground wire and see what I get, if that doesn't work, will try running a new memory wire, if that doesn't work, well, I'm not sure.
 

Kickstand

CarAudio.com Well Known
Jan 1, 2021
311
83
Maple Ridge
Check the ACC pin or blade coming out of your car for corrosion and make sure its seated properly
Car is 17 years old, stranger things have happened
Maybe run a little sand paper over it just for shits and giggles
 

2004tundra

CarAudio.com Newbie
Apr 7, 2021
8
0
texas
  • Thread Starter Thread Starter
  • #13
Update....this has to be something in the toyota computer. Got a new head unit (sent both of the other ones back) confirmed new head unit is working by connecting directly to a 12v battery. Ran a brand new separate ground to bare metal on the frame. Constant 12v wire now reads 12.65v with truck off and 12.96v with truck running. ACC wire reads 12.96v with truck running. These readings were taken from the harness that plugs into the back of the head unit. As soon as the harness is plugged into the head unit both wires drop to 1.6v. if just one wire is plugged into the head unit, both wires drop to 1.6v. Tomorrow I'm going to run an ACC wire from one of the cigarette lighters and tap a fuse for a constant 12v and see if that will work. Damn you Toyota!
 

2004tundra

CarAudio.com Newbie
Apr 7, 2021
8
0
texas
  • Thread Starter Thread Starter
  • #15
Sounds like an antitheft system. Would a 12 volt lightbulb dim if plugged into either constant or memory?
ohhhh, good question, I'll try that tomorrow. but what has me jacked up is, im not the only person to ever try to put an aftermarket radio in an 04 tundra, why can I find absolutely nothing on the interwebs about anyone else experiencing this? I just wanted to be able mp3s without the cassette tape adapter, lol
 

2004tundra

CarAudio.com Newbie
Apr 7, 2021
8
0
texas
  • Thread Starter Thread Starter
  • #16
ok, so here's an update. Im a retard, and now I understand why the harness I bought didnt match up. I just realized toyota put a little factory amp in there that I couldnt see and I had the wires that came from the amp to the factory radio, now the harness I bought matches up. Thanks to all of you for trying to help me, I really appreciate it!!!!
 

hispls

CarAudio.com Veteran
5,000+ posts
10+ year member
Sep 10, 2009
11,639
561
Central Maine
a little factory amp
Yeah, that's a wild card. Stuff like that is why unless you really want to use all your own wiring you use Crutchfield or similar to figure out precisely which METRA kit you'll want to integrate.

I'm still concerned about your <12V resting voltage though. 12.6 charging is not enough to properly maintain a lead acid battery. Might want to do some digging there and see what's going on with that.
 

Create an account or login to comment

You must be a member in order to leave a comment

Create account

Create an account on our community. It's easy!

Log in

Already have an account? Log in here.


Users Who Are Viewing This Thread (Users: 0, Guests: 4)



Newest threads

Most posts - Past 30 days

Latest classifieds