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Old 05-18-2010, 12:58 AM   #1
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Default best way to run 12v straight from the battery?

So every few times i get in the car and crank it up my lc-1 just flashes 7.4 and the only way to get it to stop that and read right is to turn off the car and wait 10sec then restart the car.

basically i want a 12v line that is always on, was planning to add a on/off so i can flip the switch and reset my wide band with out having to pull over and restart the car. plus i only have a dash harness so i have use of the cigarette lighter so i could tie that into the bat also and pull the harness.
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Old 05-18-2010, 01:21 AM   #2
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Is your 12v supply hot while cranking? There was an issue with this due to the voltage drop while cranking. IIRC the starter causes such a draw and subsequent voltage drop
that the sensor tries to recalibrate. It should be wired to a source that is hot in run and off while cranking.
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Old 05-18-2010, 01:33 AM   #3
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Quote:
Originally Posted by lordrigamus View Post
Is your 12v supply hot while cranking? There was an issue with this due to the voltage drop while cranking. IIRC the starter causes such a draw and subsequent voltage drop
that the sensor tries to recalibrate. It should be wired to a source that is hot in run and off while cranking.
i had it pulling power from the cigarette lighter, not sure where a hot wire on a 99 is.

wtb location
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Old 05-18-2010, 01:43 AM   #4
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That's where I get mine from but that's on a '92. You may want to get a test light and see if yours is hot while cranking.
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Old 05-18-2010, 09:14 AM   #5
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fuse box? maybe try pulling from gauges or radio fuse.
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Old 05-18-2010, 11:09 AM   #6
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I think the emergency light fuse is a constant 12v.
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Old 05-18-2010, 11:09 AM   #7
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I got some bling bling audio fusebox / distribution block and some 30A fuses and some 4 GA wire... like this:
http://www.parts-express.com/pe/show...number=070-850

and run a short (<12 inch) to the dist block and then your fuse and then the big wire to wherever you need it.

And yes, 30A is high, but it's mostly for the potential of grounding the phat power wire. 30A will blow before 4GA wire. Though I have seen 4GA wire vaporize in my trunk :(
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Old 05-18-2010, 12:35 PM   #8
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Quote:
Originally Posted by jeff_man View Post
basically i want a 12v line that is always on,
Well, the "best" location would be the large white wire at the alternator, as that comes direct from the battery. There's also the blue/red wire at the back of the radio, which is 10A at the "ROOM" fuse.

I'm puzzled, though, as to why you want something that's always hot. The most optimum solution to this problem, IMO, is to take power from a circuit which is hot in RUN but not in START.

In my car, I took a feed from the blue/black wire at the back of the radio and used that to drive a SPST relay. The relay takes power from the battery, through an inline fuse, and drives the LC1 & XD16.

Now, technically this circuit is hot in ACC (rather than RUN) which means my WBO2 is on anytime I have the key in the first position, but for me this isn't a problem. A better location might be the pink wire at the back of the climate control panel- I'm pretty sure that one is hot only in RUN.

The key point here is that the LC1 is disconnected whenever the starter is turning, which prevents it from seeing marginal power.
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Old 05-18-2010, 12:51 PM   #9
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Quote:
Originally Posted by y8s View Post
I got some bling bling audio fusebox / distribution block and some 30A fuses and some 4 GA wire... like this:
http://www.parts-express.com/pe/show...number=070-850

and run a short (<12 inch) to the dist block and then your fuse and then the big wire to wherever you need it.

And yes, 30A is high, but it's mostly for the potential of grounding the phat power wire. 30A will blow before 4GA wire. Though I have seen 4GA wire vaporize in my trunk :(
y8s, your fuse should be on the short wire, as close to the battery as possible. With the fuse on the wire after the distribution block, something can still short on the distribution block or pierce the short wire and short there.

I've got a similar set up from my boom boom days, using 2 ga with an 80 amp fuse, then 8 ga out of the block to my little amp. The big fuse protects my car from any unnecessary welding, and the little amp has its own little fuse to (fail to) protect itself from overload.

Edit: Nevermind, I just saw the block you linked to, it has the fuse designed into it. Not my cuppa, but at least it forces people to run a fuse, so that's good.
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