Thread: power supply wired to radio harness

Originally Posted by BCasey

Hey guys,

I've searched through a bunch of posts and got conflicting answers to this question.

So here it is, can I connect my power supply directly to the stock radio wire harness in my car?

Now I know that the problem is that the stock wires might not be big (right word?) enough to handle the current that a power supply needs.

Is it amps that cause a wire to heat up and potentially catch fire? This is my understanding. If thats the case then I think I'm ok. I'm looking at getting a DS-ATX which is rated at "Input Current: 20 Amps Max". My Chrysler 300's radio circuit fuse is a 20 amp fuse as well. So am I correct in thinking that since the power supply is 20 amps max and the fuse for the radio circuit is also 20 amps that the wires in this circuit should be able to handle 20 amps and thus it would be ok to wire it this way??

I'm no electrician so if I'm mistaken about any of this please let me know.

Thanks,
Bryan

I wouldn't chance that at all. If something goes, your whole entire electrical system could pay the price. If you use a AMP kit like most people use, the PC will be isolated from the rest of your electrical. Only thing that will be needed from your radio harness is the ACC wire to tell the PSU when to turn on your system on ignition. I have a dedicated camera system and I have one 10.2 screen on the radio harness and at least once a month I have to change the 20 amp fuse, so imagine if you connect a monster PSU to it. What is the PSU full wattage? 250? If so simply buy like a 8 gauge amp kit, but to leave room for possible expansion, install a 4 gauge kit. Do you currently have AMPS on your setup, if yes, power the PSU off of that AMP kit. Just buy a distribution block.

I actually HAVE to buy an amp kit because my car doesnt have an acc line. The radio/amp is turned on by a can bus message, so this kit plugs into the radio harness (power, ground, canbus + and canbus -) and on the other end plugs into the radio (power, ground and acc), when the "On" canbus message is recieved from the car, it will power an acc line.

The radio circuit is already on distribution block (along with other things) but the radio is the only thing on that specific circuit.

power supply wattage is 220, altho i doubt ill need anywhere close to that, i got an intel atom 330 processor which seems to be pretty light on the power and the system as a whole isnt going to be to powerful.

If most amp kits are powered from this radio harness would it be safe to assume that its ok?

Reason I'm leaning this way is because im putting everything in my dash and I could make my entire wire harness have everything in it from this one "add a head unit" module (it also has the audio wires that connect to the radio harness)

CORRECTION: The add an amp kit does NOT power the amp from the radio harness... hmm it says to connect the power and ground to the battery...

But if I wired it into the radio harness, would I have to worry about the wires catching fire or just the fuse blowing, cause if its just the fuse then whatever ill just try it and if it keeps blowing ill wire directly to the battery, but if theres any chance of a fire then i dont wanna mess with that.

Originally Posted by BCasey

If most amp kits are powered from this radio harness would it be safe to assume that its ok?

Most amps are NOT powered from the radio harness. An ignition switched line is commonly used for a remote turn-on for the amps, but that doens't power anything.

Reason I'm leaning this way is because im putting everything in my dash and I could make my entire wire harness have everything in it from this one "add a head unit" module (it also has the audio wires that connect to the radio harness)

Thanks to 2K1Toaster for this vibrant illustration:

CORRECTION: The add an amp kit does NOT power the amp from the radio harness... hmm it says to connect the power and ground to the battery...

DING DING DING!

But if I wired it into the radio harness, would I have to worry about the wires catching fire or just the fuse blowing, cause if its just the fuse then whatever ill just try it and if it keeps blowing ill wire directly to the battery, but if theres any chance of a fire then i dont wanna mess with that.

If the draw is too much for the wiring harness, the wires can heat up, melt the insulation and short out.
There's a risk of damaging equipment, causing a fire, injury and/or death for you or your passengers.
DON'T DO IT!!!

Originally Posted by csfile

I know a lot of people here say it's a risk and wire it straight to the battery. But if stock fuse is 20A, then I'm sure the car engineers spec'd out the proper size wire. That's the purpose of the fuse...to pop if it's drawing too much current before it can catch fire.

If the fuse pops, then you'd have to go another route.

WRONG!
The vehicle engineers put a 20A fuse there to protect the wiring in case of a short. That doesn't mean the wire is capable of supplying up to 20A safely for long periods.

A fuse on a piece of equipment protects that equipment. A fuse on a wire protects the wire in case of a short.

LOL. I love that drawing.
but the point comes across very clearly.

Originally Posted by chris350

LOL. I love that drawing.

Yeah, me too.
The expression on the lower fellow's face is priceless.
I have never seen such emotion captured with MSPaint...

LOL I was actually waiting for that pic to come up. So even tho theres a 20amp fuse on that circuit doesnt matter huh....

Put it this way, the main power line that feeds the radio is not just connected to the radio. In some cars, not only can it be considered the clock/memory, but I've seen it connected to power locks, dome lights, power mirrors, keyless entry, and some other stuff. So it is possible that it is powering other equiptment, and if you happen to blow that fuse, you may disable/damage other equiptment.
Here's another way to thing about it. The typical minimum size wire for 20 amps would be 12 gauge. And the typical gauge wire at the harness is either 18 gauge. In your vehicle there happens to be 2 18 gauge wire, although it would take twice that amount to equate to a 12 gauge wire (4 wires x 18AWG = 1 wire of 12AWG)