Vacuum guage install

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Apr 26, 2009
Salt Lake City, UT
So I read this tech post and I decided to install a small vacuum gauge for my 1996 FZJ80. The process is actually a bit easier than I expected and it lasted about two non-stress hours in the driveway.

Items needed:
  • Vaccum guage ($25)
  • 7' 9/16" vacuum hose ($0.50/per foot)
  • 9/16" three way brass fitting
  • Silicone grease
  • Misc hand tools

I decided to mount the guage in a less than conspicuous spot since I do not plan to always stare at it and the store did not have those neat cans to dress the gauge in. Down by the gas pedal seems to work well. I used the smaller of the vacuum hoses as this one sits behind the throttle body butterfly and it will show a more accurate and steady reading.

Here are the steps that I took:
  • Remove vacuum hose as shown in photo and discard. Use Silicone Grease to lube up the smaller 9/16" hole and assemble as shown. I used the larger dia hose to run back to the guage since it is easier to manage and will not kink.
  • Access the firewall through what I believe is the factory hole for a clutch master cylinder.
  • Dress the hose as to avoid any kinks or interference with pedals.
  • Install gauge where desired.
  • I used the illumination wire from the PWR/2nd START buttons to illuminate the guage. The wire is white/greens stripe

That's pretty much about it. It's very nice to see now how driving habits affect engine load. We're leaving next week from Salt Lake City to San Francisco to Monterey to San Louis Obispo to Santa Barbara to LA to Catalina to OC to Vegas to SLC. This will be a great decision tool in deciding between 60,65,70 mph, etc. I'm hoping to hypermile this sucker to 18-19 mpg.

Now for the 12V DC freaks out there, here a question:

When I wired the light to the gauge, I tested which lead to intercept with a test light. I found the wire that dims with the dimmer know and took it. I grounded to chassis. The light now dims opposite of the knob; turn the dimmer down, the gauge gets bright, turn the dimmer up, the gauge dims down. I'm stuck in opposite world here. Did I ground wrong?
Nice work and writeup. I'm not sure why yours is dimming in this manner. I wired mine to one of the leads coming off the fuse box under the dash (I think its the cig lighter one). However, I blew a fuse the other day for some unknown reason, so I might have to change this set up or figure out if there is a short or bad ground. I'll be that you had more room to work with wiring in your set up.

For mine, I unbolted the fuse panel, twisted it around, then pulled one of the 12v wires off the panel (cig?). I was able to un-crimp a portion of the factory connector, then crimp it back down with the gauge lights. The gauges dim/brighten with the lights and I didn't do any irreversible molesting to the factory wiring. I'm not sure why I blew the fuse because it has worked flawlessly for months now. I do know that my wife left the lights on overnight, but I don't know why that would have blown the fuse the trans temp/boost gauges are wired to.

Edit: I'll bet that you will be able to fine tune your mileage with this. Between this and the scangauge I have been able to squeeze 13-14.5 MPG city and 14-16.2 MPG FRWY corrected with GPS running 315's, stock gears and a supercharger.

Edit 2: Does your leg clear the gauge in that spot? I think that is where I rest my leg (6'1.5" w/o seat extensions)
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I am 6'1" as well (not sure about the 0.5), and it clears it just fine. I wanted to keep it out of sight as much as possible, but still visible if I wanted to see it.

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