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Wiring for a beginner

6.5K views 7 replies 4 participants last post by  Holmz  
#1 · (Edited)
First time wiring a system and I'm looking for some help. I've tried googling and searching and have found some help, but not as much as I hoped.

I bought a Sony HU that produces 45w x 4 rms. My plan is to wire that up to four 4x6 speakers and then use a sub/amp combo (focal ibus 20) under the rear seat for my low.

I want to wire my HU directly to the battery as the fuse for the radio is only 8A and I would like to use a large gauge wire. I bought some 10 gauge wire for both the HU power and the sub/amp power.

Below is a pic of the wiring harness that came with the HU and the wiring diagram from the manual. The wire is pretty small (~20 AWG?). But how do I make this a larger gauge? Do i just splice in the large gauge after the 6 inches or so of the yellow power cord? This doesn't exactly make much sense to me as I believe that small gauge connected to the HU will be a bottleneck. Or, should I remove the existing smaller power wire and wire up a my new, larger wire? That too, seems difficult and not sure if the plastic wiring harness would even accept a 10 AWG wire.
Plus, as you can see in the instructions, under #7 on the notes, it says (paraphrasing) that "during full-power operation, a current of more than 15A will run through the system. Therefore, use at least 14 AWG wire for both ground and power". And then on the picture, it shows a 15A inline fuse on the power cord next to the battery (a 15A fuse is also located on the actual HU itself). How does this make any sense? Won't it blow the fuse if a current of more than 15A is running through the system?

Other instruction questions:
On #2, I have a power antenna that extends once you turn the key to ACC, so I assume this wire (blue/white) provides the power that does that? Or is this to turn the amp on? I don't really get why there are two things this single wire does.
On #3, what is a car's illumination signal?
Lastly, above #6 on the instructions, it says (paraphrasing) "to connect the power connection to battery directly when fuse used on car is 10A, to avoid short circuits". Does that make any sense? Wouldn't the car fuse just blow, not short circuit? Also, should it say 10A or less? I don't get the reference to exactly 10A.

Thanks for all the help!

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#2 ·
Those power and ground wires look to be 14awg. The ground wire in my head unit is, and the proportions look similar, plus mine is also a Sony.

You can run power all the way to the battery if you want, but I don't think it's necessary, but if you have such a small fuse in the car, then I see why you may want to. If you do decide to run power all the way to the battery, the shorter, smaller wires on the harness won't be a problem. They will not cause a bottleneck. Wire can handle a lot more current over short runs than long runs because there is less resistance. Think about the small jumpers, and solder blobs in an amplifier, since they are short, and have low resistance, it doesn't matter.

Fuses don't blow instantly, a 15 amp fuse will need to see more than 15 amps for several seconds before it blows. With 15 amps being the maximum, you'll never reach that. Even just a couple of decibels down from max output will cut the current draw down significantly, realistically you'll be drawing less than 5 amps.
 
#3 ·
It's 18 AWG. I checked the wire and it says 0.85 sq mm. That seems unusually small for a 180w rms system right? Another reason why i want to is the car is 1982 BMW, so the wiring is about 40 years old, likely small gauge, and would like to freshen things up. I also plan to wire new speaker wire all the way around. The other wiring for the harness with the Sony stereo is 22 AWG as it says .35 mm sq.

Those last two points are very helpful. I'll match the 15A HU fuse in the new power wire as well. Should i do a 15A fuse in the 10 AWG amp/sub power power? The sub/amp is a focal ibus 20 with 150w peak / 75w rms.
 
#4 ·
Ok, if you want to beef up the wiring, and replace old stuff, you're on the right track. Don't worry about a short section of the stereo harness being a smaller AWG, it's a short section, so it won't have a big impact at all.

That sub/amp has a total of 30 amps of fusing, doesn't it (2 x 15A)? If so, fuse the power wire to 30 amps, or a bit lower. If you fuse it at 15 amps, it is possible that you'll blow the fuse even when it is working well within limits. I'm running an amp with 120 amps worth of fuses with a main fuse of 80 amps. That means that even though the amp can handle up to 120 amps, it isn't even using 80 amps, or else the main fuse would blow. Using a low amp fuse is always safe, but if you go too low then it will blow even though the amp is operating well within its limits.

Use a 20 amp fuse, 25 amp fuse, or 30 amp fuse. A 15 amp fuse will be very safe, but it may also blow prematurely.

Also, 180 watts RMS is being very generous. Realistically that head unit isn't capable of that, with all channels driven at the same time. I think half that is a more realistic RMS. Either way, wiring, and fusing to that 180 watt potential is perfectly understandable, and the safe choice.
 
#5 ·
I did notice they only tested a single channel at once... and unlike a proper 4x45rms amp dynamic burst power didn’t really go up... says a lot about the limitations of the headunit as an amp