Example: Alpine 9815, yellow wire says connect directly to battery. Why? What happens if you don't? What happens if you do? Can you harm the car or the HU? The Alpine's yellow wire is fused. So why do you have to connect directly to the battery?

 

My limited understanding of the issue is this: On HUs with reasonably powerful built-in amps the current draw can be fairly high. If you splice into a wire where the guage is too small for the power rating, you could melt that wire and cause a fire. Also, tapping into an existing circuit could cause problems with both or either circuit.

 

yup that sums up the disclaimer from alpine.

with that said, many people have wired with power from the harness (especially those that disabled the internal amp and ran it off an external amp). but a direct to battery power is what the alpine manual says to do, so that's what i did...

 

Just taking a guess here, but Alpine probably wants to be sure that their stereo doesn't cause anybody to have a car-b-que... I've always hooked aftermarket HUs up to the factory wiring. You should be ok there. The only thing I'd suggest is grounding the HU to the car rather than wiring it up on the harness.

 

rueex57 put it pretty well, aftermarket head units tend to draw more current then OEM equipment. I don't think that the wire will melt but the insulation may. I once accidently shorted a wire and saw the insulation turn brown, dissapear in a puff of smoke and the stranded wire fuse into a brown solid wire before a section melted and opened the circuit. The worst part is that other wires in the same bundle will ba dammaged also. For your information the fuse is not to protect the radio but the wireing to the radio.
Andy

 

So it doesn't really have anything to do with the amount of power the unit will produce. It will not put out more watts if hooked up directly to the battery than if it was wired to the factory harness. Its more of a safety precaution.

 

Here's a better question, has anyone running one of the new Alpine high power units that has it hooked up to the factory wiring had any of the problems stated above? Or any problems at all caused by hooking it up to the factory harness?

 

I have mine wired to the harness, but I don't run the internal amp. I think its kind of funny Alpine specifies to hook it up to the battery. I have a JVC SH707 in my beater and it has the same power rating as the Alpine and makes no mention of running from the battery.

I also think that its funny that if you go to Circuit City and ask their installers, they just wire it to the harness. Not like Circuit City is the pinnacle of car stereo or anything, but they probably install thousands of those units a year. If their installation caused a fire, it would be lawsuit city.

 

 

Systems that claim 50Wx4 (most out there) aren't a problem on the stock wiring.