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Installing an aftermarket temp gauge: Wiring questions...

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Old 01-05-2012, 01:15 PM   #1
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Installing an aftermarket temp gauge: Wiring questions...

Hi, everyone. I'm a first-time poster here but have been on and for quite a few years.

My vehicle is a 99 4runner, SR5, 3.4, auto, 4x4 with the rear locker. Currently at about 142k miles.

Anyway, I've run into a problem that I can't seem to find an answer for. I did a search but couldn't find anything that helped.

Here's my issue: I want to install an aftermarket outside temperature gauge so I know the temp outside (most modern vehicles have these but my 99 SR5 doesn't.) I've been running a cheap outside thermometer for the last couple of years, but it has a few drawbacks, primarily they are that I can't see it at night (not backlit as it runs on a single AAA battery) and it looks like crap stuck on my dashboard.

Now I know they make those mirrors with the outside temp display, but I don't like them. They also seem rather expensive (around $150 from what I've seen.) So, I went ahead and got an aftermarket electric 2 1/16" gauge and a pillar-mounting pod from

Now I'm not a mechanical whiz by any means, but I can operate a screwdriver and a pair of pliers. However, this install has me a bit confused. In order to install the gauge, I need to tap into 3 locations: A ground, a 12v power source that is only powered when the ignition is on, and a source that is only powered when the lights are on (to activate the 'dimmer' on the gauge.)

Seems to me the ground is easy - I should be able to ground to a body screw or bolt, right? But the other two - where and how can I find the correct wires? I have had the lower dash off my 4runner before, so I know where the fuse block is, but it just looks like a mass of spaghetti down there. Not only that, the wires are tiny - I'm afraid of trying to cut into one of those little wires for fear of screwing something up in the truck that would cost a lot of $$ to fix.

So, any tips as to where I can find a couple of wires to connect to? Has anyone out there installed a similar type of aftermarket gauge into the driver's side A-pillar?

Thanks in advance. If/when I get this figured out I'll make sure to take lots of photos and post it up in the appropriate section of this board.
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Old 01-05-2012, 02:26 PM   #2
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You want a test lamp. Its a probe with a sharp point that can pierce insulation and the other end is a lead that clips to an earth. When current flows it lights up a small bulb in the probe. My last one cost me NZ$10.
Also If you have the FSM (Search on here, someone will have it) you can look at the wiring diagram and see that switched power is Red with a Yellow stripe (for example) and then you are just confirming with the test lamp.

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Old 01-05-2012, 02:36 PM   #3
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why not buy one of those little fuse taps that splice directly into a fuse... I'm not a fan of them, but then again I'm not a fan of people hacking up their wiring either, unless you know what your doing, solder, and use heat shrink.
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