At a loss - new head unit not coming on?

ThxOne

AudioFreak
5,000+ posts
Jun 8, 2018
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Black - Ground
Red - Switched ignition
Yellow - Constant power (should be fused) if not on the yellow wire itself then there should be a fuse in the back of the head unit.

Twist the yellow and red wires together
Touch and hold the black wire to the negative battery terminal
Touch and hold the twisted red and yellow wires to the positive battery terminal

The radio should turn on fully.


Always check all the fuses!
Make sure you have the correct harness for your car/boat.
If not, run your own ground to the body or firewall and not to a random piece of metal behind the dash.
Test the switched 12 wire (ignition turn on power for radio) and see if it comes on when the key is turned on.
Test where the yellow wire is getting power and make sure it has power all the time and that it's the correct power (12+ volts fused) If this wire from the car is not making power it may be the incorrect wire or its fuse may be blown.

Of course your battery may have dead cells and if that is the case it will light up low voltage things like led lights (USB port) but not the radio. Have the battery tested.
 

mbrown1782

CarAudio.com Newbie
Jun 21, 2022
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Thanks for the great tips ThxOne. I dont think it matters, but this is in a boat. The battery that I'm using is fully charged and holding about 14.4 volts. All the in-line and fuse block fuses have been checked and verified. The wiring harness that im using actually came with the HU - so I know it's right. I will twist my wires together to check them to see if that works!
 

ThxOne

AudioFreak
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Jun 8, 2018
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Thanks for the great tips ThxOne. I dont think it matters, but this is in a boat. The battery that I'm using is fully charged and holding about 14.4 volts. All the in-line and fuse block fuses have been checked and verified. The wiring harness that im using actually came with the HU - so I know it's right. I will twist my wires together to check them to see if that works!
It is all about tracking down the source of the problem. If it is wired directly to the battery and works you can eliminate that and work your way back to where the radio is mounted.
 

mbrown1782

CarAudio.com Newbie
Jun 21, 2022
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Ok - running everthing directly to the battery worked. Visually all the fuses looked good but I'll just replace them all anyway. After that, what do i need to do?
 

ThxOne

AudioFreak
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Jun 8, 2018
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Ok - running everthing directly to the battery worked. Visually all the fuses looked good but I'll just replace them all anyway. After that, what do i need to do?
That means it's most likely the harness. Test each of the wires (Yellow, Red, and Black for continuity). Check for corrosion at any junction for the wires. Check the ground wire for corrosion. Make sure battery terminals are clean, tight and secure first.
 

mbrown1782

CarAudio.com Newbie
Jun 21, 2022
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  • #21
Since i dont really use the clock or all that memory stuff, can I just twist the red and yellow wires together on the wiring harness and attach them to the red or yellow "hot" wires?
 

mbrown1782

CarAudio.com Newbie
Jun 21, 2022
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PS - the yellow wire has a 15a inline fuse, the red wire has a 1a fuse and the HU also has a direct 15a fuse in it...
 

ThxOne

AudioFreak
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Jun 8, 2018
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Since i dont really use the clock or all that memory stuff, can I just twist the red and yellow wires together on the wiring harness and attach them to the red or yellow "hot" wires?
No, it will be a draw on the battery even when powered off at that point. Keep the red and yellow separate. You can put a toggle on the yellow to cut power for storage.
 

mbrown1782

CarAudio.com Newbie
Jun 21, 2022
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Can i wire them both directly to the battery (after the inline fuses). I turn the batteries off after we put the boat away every night (or especially if we are gone for a week or so). I could simply disconnect these wires if i had them connected with alligator clips or something?
 

mbrown1782

CarAudio.com Newbie
Jun 21, 2022
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  • #26
I ran a line directly from my battery to the yellow and red lines on the wiring harmess that i twisted together. I didnt have a toggle switch (i will put that in next trip), so for now, I am just taking the radio battery wire off at the post (I connected via an "O" connector I put directly on the positive post) when we leave for a week or so...
 

Coolhand20th

CarAudio.com Elite VIP
Mar 27, 2019
2,438
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If you had to run new wires that tells me the old head unit was fine and that there is a break someplace in the wiring you have now. I would be checking all of that out and finding out why or where it is broken or not connecting before running new wiring. Has to be a reason for this, it just doesn't happen without a reason.
 

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