I swear I've searched everywhere, and can't find this anywhere else! I ran power from the fuse box to my new h/u. I have power when the ignition is ON, and there's no power when the ignition is OFF. Great, right? Except that I also have no power in the ACC position. Am I just tapping the wrong fuse? Does anyone know of a fuse I can use to accomplish this? HELP!!

m@

 

sounds like you need to tap into an acc wire... One can be found under the steering wheel. Anyone have a pic of that area? I forget what color the wire is...

 

Is there some sort of terminal under there? or is it just splicing the wire? I like the "un-do-able-ness" of adding a terminal to a fuse. I suppose I'll do what I have to do to get it right, but I'd prefer not to cut wires if I don't have to. --Are there not any ACC fuses?

 

Why are you even running wires? I assume you are replacing the factory head unit with a new one? If so then all the wires are already there in the dash from the stock unit. Just get a wire harness adapter, plug it in and you are done. No need to run any wire, splice thenm or tap to the fuses. BTW you should never tap to the fuses if at all possible as it ends up spreading out the terminals at the fuse box and they eventually get loose and won't hold fuses properly.

 

GREG S - Thats not true, infact the adaptor I bought specifically says "This vehicle and adaptor is not equipped with a +12 switched ignition wire, you will need to run a seperate +12 volt ignition source. We recommend wiring to the fuse block, or other such power source."

I actually have the solution to this. On mine, on the factory wire harness there is a purple colored wire that is not being used when connected to the harness adapter (I assume you have one) this is actually the switched ignition wire, just get your +12 ignition power from this wire because its not being used other than with the factory deck anyway and everything should be fine.

 

^^ the factory HU is not switched... you can turn it on even with the
key in your pocket. i found this out while doing my Autoup window
install. this is how the HU is wired from the factory.

so yes, you will need to find another source for the switched power...
i would say, just tap your remote wire to the cigarette lighter wire.

you need to run your main power to the battery anyway, no?

 

semipro is right, the recommended harness doesn't have a switched power wire... Unfortunately, mine didn't have the recommendation to use power from elsewhere.

Kenchan - Good point on the factory hu not being switched, I never thought about that, at least not when I was doing my install! I suppose it just had constant power.

Semipro, is that purple wire intended to run switched power to a factory cd changer?

 

NO Headunites are fully switched. They get their power from always-on power (red and black). In addition they have a yellow, switched, ignition wire that is switched with ignition. But all it really does it tell it to turn on, it doesn't actually draw its power from this wire! Goes for any aftermarket radio. That way, its clock still runs, and you can hit the on button to listen when the car is off.

That ignition wire should be in there with the stock harness, but if not, you can tap fuse 36. http://www.jwardell.com/mini/fusetap.html

 

All after market head units are designed to be ran from a switched power source. And that is the RED wire, (12+ Switched) the yellow you are reffering to is the +12 Memory Lead (always hot, keeps your clock right, stations in memory, etc). And on most cars, you can not just hit the on button when the key is not in the ignition and have the stereo turn on, in fact this is the only car I have ever seen do that (with the factory deck in).

And the purple wire is still a mystery to me and to my buddy who installs audio in cars, because on the factory deck it is being used, but that makes no sense because the deck is able to be on when the car is off, and this purple wire loses its power when the ignition is off.

But, you can use this wire as a +12 volt power source, it is better and safer than going to the fuse panel.

Hope everything goes well.

 

i suppose for people that run external amps this is true. but for
those that run built-in amps in the HU that pulls alot of power,
i would pull the power directly from the battery... ie: on the MCS,
tap a ring terminal onto the fat wire that feeds the fuse box under
the bonnet.

 

I think your misunderstanding what I am talking about.

He is referring to a 12+ volt power source that is switched for his aftermarket HU. He isnt referring to an amp, and if he was referring to an amp, there is always a blue wire (sometimes has a white stripe on it too) that is the remote lead. And if theres not a remote lead there is a power antenna lead on the HU wire harness. Either of these is the proper wire to tap a into to make your amp turn on when your deck is turned on. If you use any other power source that is not ran off the deck, and you turn your deck off with the power button, your amps will not turn off.

oh and just so you know, you never should have to run any power source for a HU to the battery, there is no HU on the planet that takes that much power.

 

Feels a little warm in here!
I've never had to run a line from the battery to a hu before, seems like overkill to me. (In all my "vast" experience installing 5 or 6 radios) What wanted was the switched power (red wire). The yellow is indeed the "always on" memory 12v feed.

On the subject of the purple wire... while a line to the battery sounds like overkill, the purple wire seems very small. Smaller, in fact, than the yellow 12v line. My fear is of melting that wire somewhere up the line if the amp in the HU draws too much. thoughts?

 

not really. he's just making a point as I made mine.
If you've ever wired up higher power HU's with built-in amps,
the manual will tell you to run a direct wire to the battery. Ive
had to do this on several occasions on 2 of my previous cars and
a few on my buddies cars running an Alpine HU. i forgot which model
it was but it was like $400.

It gave you a choice to run the internal amps or run external
amps. if running external amps, you can just tap into the harness
or run a quick wire to the fuse inside the cabin and no direct wiring
is necessary.

but anyway, back to your questions.

 

You're right I forgot about BMW doing main power from the constant line. You can use the purple wire and a relay to trigger a switched line though and still not have to run a power line or tap the fuse. This is what I used to do on older VWs for a switched line.

As for running a power line directly to the battery, that is necessary for some radio, most notably the higher power Alpines, but most radios do not need it. I still do not like to tap a use as of how it will spread the pins out over time. I've seen it way too many times over the years and refused to do it when customers would ask me to. I always preferred to tap lines directly from the key an fuse them seperately.

 

ok, so let me summarize what I think I've learned, you tell me if I'm right, or still clueless!

If I attach the purple wire to the switched power (red wire) on my HU, it will only use that wire to pull an "on" or "off" signal. The actual power to run the deck will still come through the "constant on." Does this sound right?.....

 

StJames,
Your summary is exactly right...... The purple wire is "switched power". It will work fine to trigger the unit to power up when the ignition is turned on.

 

Stuck!

When I turn my ignition on, my deck powers on, but when i turn the ignition off, take the key out, get out of the car, lock the car, my deck still stays on!

What did I do wrong, I think its my accessory wire, I was using a add a circuit in the fuse box but maybe im using the wrong one?

Any Ideas?

 

Did you splice the power into the cigarette lighter? If I'm thinking correctly it was an option for the cigarette outlet to stay on 10-15 minutes after you turn of the ignition or something like that.

 

I didn't splice into the cig lighter but I did run a lead from that same fuse. Any way of changing the time it takes for that to shut off or another fuse I could use that shuts off instantly?