How to: calibrate speedometer and tach after needle removal Options

[stephen_lee]

So, many of us from time to time have removed the needles to our gauges for various reasons, end up setting them back at the wrong place, and may never even notice it. So I took my spare gauge cluster and found out the most accurate way of setting the needles. I took a tone generator and found frequencies that correspond to various speeds on the gauges and made 1 minute recordings of these frequencies for you. READ AND UNDERSTAND WHOLE HOW TO BEFORE ATTEMPTING ANYTHING


1st, find a reliable source of 12V, may be your car battery or an old AC adapter. Find the positive and negative wires on the AC adapter, if used. My particular adapter had a black wire/white stripe for its positive wire.

Connect the positive lead to the "IG+" terminal behind the speedo, its the bottom left screw. Connect the negative lead to the "E" terminal, the bottom right screw behind your speedo. (black wires in the pic)


2nd, find a way to get an audio signal to bare wires, could be a cut pair of head phones, or just the speaker out from your amp. Either way, you take the one lead from your audio signal and connect it to the "E" terminal behind your tach, it is the bottom screw. Then you take the other audio lead and connect it to the "SI" terminal behind the speedo, the top left screw.
(refer to pic above, audio signal is the larger clear wire)

NOTE: the signal must be pretty loud, so just a plain laptop may not work, i suggest using an amp, or speaker lead from your head unit.



You are now set up to calibrate your speedometer. You are only missing the audio signal!
Turn down your audio source completely, and prepare to play a test tone provided at the end of this how to.
Attach your needle loosely to the gauge, play the tone and slowly turn the volume up until you see the needle move and stay steady.
Start the tone over. Remove the needle, realign it to the speed corresponding to the tone being played. You only have 1 minute.
Turn the tone off, and back on, verify the needle goes to the same speed. Play the other tones and verify they line up correctly.
Speed may be 1-2 MPH off due to internal/mechanical resistances, but the tones themselves are very reliable.
If the speedo does not move when playing a higher speed, turn up the volume, its less sensitive the higher the speed.
150 MPH point will need a bit of "help" to get it into the the right half of the gauge due to the way the magnetic gauge works.





Okay, now your speedometer is calibrated, you need to set up to calibrate your tach, but don't worry, you only need to move one wire!
Disconnect your audio source from the "SI" terminal, and connect it to the "IG-" terminal behind your tach, it is the top screw.




You are now set up to calibrate your tach.
Attach your needle loosely to the gauge, play the tone and slowly turn the volume up until you see the needle move and stay steady.
Start the tone over. Remove the needle, realign it to the RPMs corresponding to the tone being played. You only have 1 minute.
Turn the tone off, and back on, verify the needle goes to the same RPM. Play the other tones and verify they line up correctly.
Speed may be 25-50RPM off due to internal/mechanical resistances, but the tones themselves are very reliable.
If the Tach does not move when playing a higher speed, turn up the volume, its less sensitive the higher the speed.


You have now finished calibrating your gauges!

20MPH Test Tone
35MPH Test Tone
70MPH Test Tone
150MPH Test Tone

1000RPM Test Tone
3000RPM Test Tone
5000RPM Test Tone

EDIT: Email me for test tones. sallen(at)oscenter(dotcom) [nospam]
I moved and can no longer host files due to no high speed internet access.


Disclaimer: I am in no way responsible if you kill your gauges somehow. I hooked up my power backwards long enough to get smoke, but it all works still.
Easy way to tell if your power is hooked up right, your fuel gauge will gown down if power is hooked up correctly, and up if reversed. Toyota has some
pretty hardcore gauges lol

This post has been edited by stephen_lee: Sep 17, 2009 - 12:14 PM