New head unit wiring question.

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J

jwldane

10 Year 15 Year
Joined
Dec 19, 2007
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12
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Hi.

I apologize but I have searched and searched but I cannot find a definitive answer. I'm sure it out there but I can't find it.

Here is the problem:

New Boss head unit. Double DIN touch screen. Bluetooth, backup cam, etc, etc. I know it is a cheap unit but I am happy enough with the sound on the stock system, but I wanted to add the convenience of a more modern unit. I bought the harness adapter to maintain the original amp. 15 Pin for 99 LC. New HU has front L&R preamp outs.

I have tried connecting the wires in various ways with varying results but still not right. I have gotten power to the head unit but no sound, I also have gotten a loud hum and also a load higher pitch sound. I have also heard a very faint sound thru the speakers that sound like the horn.

Now I have yellow to yellow, red and blue-white, to red, black to black. Still no power at head unit.

Question...does the blue/white wire turn the amp on.....or does it bring power from the amp the stock HU? If I have to tap power for HU from the stock amp which wire from the amp do I need to tap? By using the stock amp, is it correct that I should only have to use the preamp outs from the head unit to the front L&R rca jacks of the wiring harness adapter?

All of this use to be really simple back in my youth, and I thought this be a walk in the park, but I can't seem to find the right combination of connections. Can someone please teach this ole' fool which wires to connect together.

Thanks
 
Thanks OregonLC.

Very helpful, but I do want to use the OEM amp and sub.

Took the old multi-meter out and checked the following:

With ignition switched to on and from the harness adapter:

Yellow = no power
Red = 12volts
Black = good ground
Blue white = no power.

So I think to myself that if I just use the red and black I could at very least power up the new head unit. Nope. No such luck. I am still confused. Head unit fails to turn on, antenna wont go up. Starting to think it may be a bad head unit.
 
If you suspect a bad head unit, connect the power and ground wires directly to a 12V source like a battery and see if turns on.
 
Blue/ white as a standard for aftermarket head units is an output, not an input. It is the amp turn on. Have you checked the fuse on the back of the head unit? The amp feed is brown/red. From tlc's description, it looks like batt pos and negs feed through the amp to the head unit. The brown/red amp reference voltage goes to the amp.
 
Latest update.
Connect red to + battery terminal
connect black to - battery terminal

Head unit does not power up

Connect yellow and red to + battery terminal, black to ground.

Head unit powers up, CD ejects.

In dash, I never get power to the yellow wire on the oem harness. What fuse protects that circuit? That may be the problem. Or if the yellow gets its power from the amp but the amp doesn't get the signal to turn on, then that may be the issue.
 
Look at your head units wiring diagram. Yellow is supposed to be battery constant. This is for radio memory. Red is supposed to be 12v switched, which powers the radio for normal operation. That's why someone told you to bench test with just the red and black. Your radio is odd. Which wire pin on the stock pigtail corresponds to your yellow on the radio harness?
 
I had the same and I by-passed the factory amp.
Problem solved, clear sound but lost the sub.
Be aware that the power to the radio comes from the amp.
 
Thanks for the responses.

Gonna give it a try again today.

It seems that in order for the HU to turn on it must be getting power to the red and yellow leads.

I still have not determined why I do not get power to the yellow. Yes it is supposed to be a constant 12v source but I do not get power regardless of the position of the ignition switch. It has to be a fuse or the power to the yellow must come from the amp when the amp is switched on.

I have a blue and white on the harness adapter labeled "Signal to turn amp on" but there is nothing on the HU harness to connect it to. At this point I still do not know where this blue/white should be connected.

All other connections are standard:

Red to red
black to black
blue to blue (antenna)

So there question remains; 1: Where do I connect the blue/white to turn the amp on?
2: Shouldn't the yellow always be hot, and if so is the fuse in the DS kick panel?

All other connections are for speakers, mic, USB, camera.

Thanks again
 
Since you are stuck, see if you can try the following. Run a fused wire from batt pos to the yellow and red on the head unit. Hook the harness up with the ground and one speaker so you can get some sound. The stock amp batt positives and grounds feed the amp first before the hu. Even if it is a feedback loop, the feedback should be through that amp turn on wire. This means the amp should have power and grounds, with the exception of the turn on. Now that I've probably confused you, I'll continue. Connect the blue/white from the hu to the brown/red in the harness. That should simulate "completing the loop" if the loop is voltage based and not frequency based. (Meaning the amp would be looking for a square wave input)

The yellow should be always hot. Do a search for fuse panel identification and check all fuses in the radio circuit. If everything is good, simply use a multimeter to check the vehicle radio harness for which wire has power all the time.

I was going to attach a complete wiring diagram for you, but my Mitchell ProDemand software doesn't provide one at all for the LC100. The lack of information upset me some, since we pay so much per year for this program.
 
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Also, see if the gray wire on the vehicle harness side has batt pos voltage with the key on. I'm not sure whether that wire is an output or input of the amp, so checking that will answer that question.
 
Since you only have "blue" from your HU, hook "blue" to both "blue" and "blue/white" from the harness.
Having both is a nice feature because the antenna only goes up during am/fm and goes down when listening to sat or ipod etc.
Your antenna will always go up, but you can manual put it down if needed with the antenna button.
 
Thanks again for all the help.

Yesterday I tested the HU and the unit powered on with the yellow and red lead directly to the pos battery terminal.

I know that the red lead from the harness goes hot when the ignition is switched on, so I connected red and yellow from the HU to the red from the harness. Of course, black to black for ground. Blue to blue for antenna. Hook up speakers directly from HU.

Turn on key, turn on HU and the unit powers up, the antenna goes up two inches, lights on HU go out and back on, I get a momentary sound from the speakers, the antenna goes down, not necessary in that order. Then the whole process loops again and again. It is like the HU is continually cycling thru power on and power off phases. Weird.

I am guessing at this point the head unit is toast.

Still no power from yellow lead on oem harness. Checked fuses and everything looks OK. At this point......frustration gets the better of me and I quit. I will check out and report on the other wires coming from the harness. The connecter is so small, its difficult to get the multi-tester probes to touch the contacts. Need an extra pair of hands.
 
Oh I didn't realize you were saying the yellow wire that didn't have power is on the OEM harness side. If you have the non-premium sound system with regular six disc CD changer and then that yellow wire is the right front positive speaker Signal wire. When you bench tested the head unit did it cycle through power like that? Can you take a picture of your OEM side radio pigtail?

For getting on the pins of the radio OEM pigtail you can use a paperclip or bobby pins.

Something I forgot to mention earlier- you won't be able to just hook the speaker outs from the hu to the factory harness, because that stock amp is not designed for high level inputs. You need low level inputs (rcas). There is a special harness adapter for the LCs that have that. Does your harness have rcas?
 
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Thanks for the help everyone. Especially Ermagerd.

I have decided to have the system installed by pros. Going in this afternoon. Now we'll find out if the unit is trash or I have an issue with the LC's wiring.

Thanks again.
 
For what it's worth, your harness wiring might not match what is on TLC's site. My LC is a '98 non-premium system. I have a 15 pin connector with a different pinout and wire colors than what's on TLC's site. I figured out most of the connections, but maybe not enough to run the stock amp on an aftermarket hu. (I put an aftermarket amp in)
 
jwldane said:
Thanks for the help everyone. Especially Ermagerd.

I have decided to have the system installed by pros. Going in this afternoon. Now we'll find out if the unit is trash or I have an issue with the LC's wiring.

Thanks again.
Click to expand...


I am dealing with same exact issue...I'm assuming the pros got it to work? Any idea how?
 
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