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Old 08-23-2014, 07:08 PM   #31 (permalink)
Is this thing on?
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Gauge Illumination question

Hi all-- thanks to this thread I have a nice vacuum gauge working. ( Various problems with fittings and when I first tried the gauge, it read about 11. I deduced that the hissing noise at the gauge fitting might have something to do with it.)

Anyway, now I need to wire up the bulb. I thought it would make most sense to wire it into the instrument panel so I could get the dimmer working. But how do know which wire is the wire for illumination? I have spent many hours searching the web for wiring diagrams or info like, "dash illumination is ALWAYS the yellow/white wire". So, I'm stumped. Here's a picture of the dashboard wiring harness). Anyone have any suggestions or an easier way to do this? Many thanks in advance.

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Old 09-07-2014, 05:24 AM   #32 (permalink)
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to tap into the dash lighting, i grab a volt meter, turn the running lights on, stick the negative lead of the meter on any exposed frame i know is a good ground, and stick the positive lead on each terminal until i find 12 V. then i turn the lights off and confirm the same terminal has 0 V at that time. next i do the same thing but keep the positive lead on the known dash light terminal and move the negative lead from terminal to terminal until i find the ground wire. once i know which both of those are, i splice into the wires using scotch connectors and connect them to the vac gauge bulb. some people don't like to use scotch connectors but in interior applications that will not see any exposure to moisture or whatever, i find they are fine.
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Old 11-05-2015, 05:26 PM   #33 (permalink)
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So glad I found this thread. Can you tap into the PCV valve line? I have no other lines to easily tap in to. My PCV line runs straight from my manifold to the tappet cover with the valve on the tappet cover side. I simply want to add a piece of hose and T piece to the manifolds side and re attach the hose onto the extension without cutting it. Will this work? Will the valve opening and closing during throttle positions effect the reading? I want to install this weekend so any feedback would be greatly appreciated thanks.

Last edited by Eddie25; 11-05-2015 at 11:50 PM..
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Old 11-06-2015, 01:33 PM   #34 (permalink)
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Originally Posted by Eddie25 View Post
. Can you tap into the PCV valve line? I have no other lines to easily tap in to..
Tapping into the PCV valve hose would not work very well. Generally speaking a vacuum metering instrument be it a vacuum gauge or MAP sensor ideally you would want its own port. If that is not possible You want it to be on a line that does not have any actual flow. A good source for this would be the fuel pressure regulator vacuum line (if on a fuel injected vehicle ) or the vacuum line leading to the solenoid for the EGR

Look at mediately behind the throttle body about you should see a couple vacuum lines regardless of vehicle manufacturer approximately a quarter of an inch in diameter

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Old 11-11-2015, 07:05 PM   #35 (permalink)
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When I installed my vac gauge I hooked into the vacuum line feeding the brake booster. Since that's the one place you know you'll want all the vacuum you can get, you know that's the one place it won't be metered or otherwise interrupted anywhere. A couple of vac sources are like that.

Do, of course, make sure you aren't hooking in "downwind" of the check valve that holds the vacuum in the booster. Your vac gauge will go right up and stay there even when you turn the engine off. Weird and obvious when you think about it.

They recommend against it citing safety reasons, but mine has been on for a few years now and has presented no issues whatsoever. In fact the gauge has been less reliable than the plumbing, but that's another story.


Lead or follow. Either is fine.
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