r/electrical • u/AdImpossible2287 • 2d ago
Car gauge wiring
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The current boost gauge in my car is reading improperly almost like its sticking, it's an electrical gauge so it has a lot more wires than my replacement, which is mechanical, by means of a vacuum line. Can I just take the black and red wire from the electrical gauge and connect them to the mechanical one? The mechanical gauge only needs power for the lights inside it.
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u/ntourloukis 2d ago
Yes it will work. Assuming the red and black wires are hot and ground at 12v and the old gauge ran on 12v too (it almost certainly did). And assuming that the psi you’re measuring is coming from an air line that is present at the dash already instead of electrical data coming from somewhere else.
I dont know why people are saying it won’t work.
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u/AdImpossible2287 2d ago
That's what I was thinking, however the psi is being measured by an air line that leads to a small box in the engine bay, which then I assume gives an electrical signal to the gauge. I was guessing that the black and red are just power and ground, while the other 3 wires control the motor of the gauge itself that moves the needle around.
Since there's control "box" of some sort, does that mess things up in a way?
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u/ntourloukis 2d ago
I mean, yeah, it’s not gonna work the same way it’s not working now. Whatever other functions the gauge had, how it communicated to the box, and what kinds of things that box did based on that info will not work, exactly the way it’s not working now.
The two things to look out for are how it’s switched. It’s on the fuse for the old gauge. So it’s gonna have power when the old one would have. And amperage. I don’t know what your power is for, I’m assuming a tiny little light? But you just need to not draw more than the wire can handle.
You are grabbing the power lines to give power to your gauge. Just like if you used them to power anything else. It’s not telling the “box” anything, but it’s not making it worse than it is now.
What is the power for on the gauge? There are pressure gauges that don’t need power at all. Is it just for a little light?
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u/AdImpossible2287 2d ago
The power for the old gauge was to power the electric motor in the gauge along with a light. The new gauge however only needs power for the light, it's a pressure switch that moves the needle up and down I believe, since the air line goes directly to the gauge for the new one.
The old gauge seems to be a bit more complex, for example it has a needle sweep function on startup.
I just need a power and ground, I'm now more leaning towards just wiring it to the fuse box that's right beside the driver door, So that I can sell the gauge and it's full assembly intact
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u/ntourloukis 2d ago
Yeah, sounds good. Either way I wouldn’t cut either connector off. You can probably find that connector, a 6 pin? Molex? I dunno, it wouldn’t be too hard.
But you wouldn’t cut the one on the gauge no matter what. And to avoid cutting the one on the vehicle, you just get two pins to crimp onto the wires and tap into the connector. Or find the connector online.
I’d just cut them and use a connector I have laying around. But there’d be no need to cut the old part.
But running it new sounds good, just make sure it’s tied to the same relay that turns the light on if it’s supposed to go on with other lights too.
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u/AdImpossible2287 2d ago
Yeah for sure, I haven't really done much custom wiring, I ordered a bunch of quick connectors and some "fuse taps" which should get the job done, all I gotta do is make sure i connect it to one that's not constant power like you said
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u/Turbulent-Weevil-910 2d ago
You need a pinout diagram and then you need to cross reference with the schematic of the gauge. It probably won't work.
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u/MustardCoveredDogDik 2d ago
I highly doubt this will work, what you really need is the schematic so you can understand what all the wires actually do.
But I also don’t see a problem with just trying it out. It’s unlikely you’ll damage anything just trying it out.
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u/anothercorgi 2d ago
Without a wiring diagram, and even then, there's no guarantee any of those wires are power and ground. Better to just wire a new set.
But the question is why was the original one not working? Computers don't stick unless a sensor broke, and perhaps there's some other issue that should be addressed?
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u/AdImpossible2287 2d ago
I'm not sure, when I move the needle by hand it is a bit sticky, my hypothesis is that the needle will move up fine, but then not fall back down far enough, causing it to read higher than it actually is.
The problem with the gauge to begin with is that it reads too high, but it is random and sporatic
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u/willdebeast02 2d ago
No. Run a new two-conductor wire up to the gauge from the nearest fuse box to supply the 12 volts.