12v power source - fuse box?

[Jimnist]

Hey everyone,

I recently installed a water temp gauge but have a slight hiccup; the backlight illumination does not switch off as i believe it's getting a constant 12v power even with the key in the 'off' position. The acc wire was wired in properly as the needle moves all the way to the left in a typical off position. Right now, it's spliced into the 12v source for the headunit.

So i was wondering, is there a empty fuse/relay spot i can use a fuse tap connector and get the juice from there? If i were to use spot where a fuse used to be, should the be a specific range of amps that it should be in (e.g. 10A-20A) and what side would i plug it into? There was a 'fog light' fuse on the sticker, but i don't have foglights nor could i find the fuse 'hole' for it. Haven't seen the relay's properly.

My camry is the base model avail in Australia with the only factory upgrade being the air-conditioning (confirmed with the original receipt for the car); no power mirrors, windows, central locking e.t.c....

You may think i'm going to some trouble when i can just wire in a switch, but it's a lot easier finding a empty fuse or relay that will cut power when ignition is off rather than turning the guage on and off every single time i get in the car.

[Mike Gerber]

"Right now, it's spliced into the 12v source for the headunit."

There should be 2 power sources for the headunit. One with constant 12 volts so the headunit will keep it's station presets and memory on where it was playing a CD when the car was shut off. It will also have another 12 volt source that turns on and off with the ignition switch. You obviously tapped in the the constant 12 volt source. You just need to find the ignition switched 12 volt source for the headunit and tap in to that one or as you said, find a 12 volt source from any unused fuse holder in the fuse box. You need a digital volt/ohmeter to test for a fuse source or a simple 12 volt test light will also work. Just ground the end of the test light to any bare metal ground and touch the sharp probe of the test light to any empty fuse box source with the ignition on. If the tester lights up (or shows 12 volts on the digital meter if that's what you are using) 12 volts is present there. Then do the same thing with the ignition off. You don't want the test light to light up with the ignition off. If you tap in to the fuse box the item will dictate it's own amount of amps. If you go this route I would just add an inline fuse to the wire rated just above the amps that the item is drawing. The paperwork that came with the gage should tell you how many amps it draws; if not, call the manufacturer or check their website. This really is pretty basic and you should be able to do this.

Good luck.

Mike

[Jimnist]

Yeah, i guess it was the constant 12v for headunit memory*slaps head* Doh!

I have an aftermarket harness that i bought from an Auto store which has all the wires labelled It said in the instructions that it should be connected to a constant 12v, guess it's wrong. Hmm...the main ones coming off the headunit are:

1) 12v constant. Currently connected and, wire says it's negative
2) 'ACC' - Connected to 'acc' for the gauge, wire says it's positive.
3) Ground.

So i guess i should wire it into the 'acc' for the power then? Is there actually a polarity difference?

[Mike Gerber]

Originally Posted by Jimnist

Yeah, i guess it was the constant 12v for headunit memory*slaps head* Doh!

I have an aftermarket harness that i bought from an Auto store which has all the wires labelled It said in the instructions that it should be connected to a constant 12v, guess it's wrong. Hmm...the main ones coming off the headunit are:

1) 12v constant. Currently connected and, wire says it's negative
2) 'ACC' - Connected to 'acc' for the gauge, wire says it's positive.
3) Ground.

So i guess i should wire it into the 'acc' for the power then? Is there actually a polarity difference?

Test it with a 12 volt test light to be sure, using the procedure I described above. You can pick one up for a few dollars at any auto parts store. Add it to your tool kit. Here in the states I have even seen cheap verisons at dollar stores. Cheaply made yes; but they do work. I carry one of the cheap ones in the tool kit I have for every car we own.

Mike

[Jimnist]

Well, haven't got around to yet - yes, i'm a great procrastinator. I was thinking, maybe it suggested the headlight in the instructions as it doesn't actually power the gauge, but just the backlit illumination. If this were the case, what would be the easiest way to wire it in so that it comes on when i turn the lights on? Would doing it through the rheostat/dimmer switch work?

And thanks for the tip with the multimeter, didn't really occur to me to use one lol. Electricals scare me

[Mike Gerber]

Why not just tap in to the wire for the headlights (for the backlight only), since you want it to work in conjunction with them. Not sure about the dimmer switch.

Mike

[Jimnist]

Originally Posted by Mike Gerber

Why not just tap in to the wire for the headlights (for the backlight only), since you want it to work in conjunction with them. Not sure about the dimmer switch.

Mike

Wasn't sure which wire was for the headlight, i thought of the dimmer switch as i know where it is and there are only 2 wires coming off it

Doesn't matter now. I got around to it today and just re-soldered the wire for backlight into the ACC for the radio. I tested it with the multimeter beforehand and it was a-okay. Funny thing was, when i tired the constant 12v, it didn't register a reading. I guess my ground was bad; i was using a bolt on the door. Now that i think back, i could've just stuck the probe into the ground coming off the harness, i'm so stupid

Thanks for your help, Mike.

Edit: Hooking it up to the headlight would be nice, but i don't like the idea of cutting into the factory harness since the radio was already there (wire stripped and ready).