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| V6 Tachometer Schematic (Page 1/2) |
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PePe-LePu_For_2
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MAY 12, 02:10 PM
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V6 Tachometer Schematic
Because I could never find a schematic of the tachometer used in my V6 Fieros, I decided to reverse engineer one and create a schematic. The board featured here is GM P/N 25071424B it is out of an 88 GT. It uses an LM1819 Air Core Meter Driver IC having GM P/N 25054339. If you download the data sheet for this now obsolete IC, you will notice a reference design schematic. The engineers at GM closely followed that example but not at the100% level. One of several deviations is the use of a resistor network for which I have assigned the reference designator RN1. This resistor network contains five of the seven resistors used in the design. If you remove RN1 from the board and turn it upside down, you will see the pinout printed on the underside. I used that pinout to identify the individual resistors on the schematic as well as on the PCB. All resistors and capacitors were lifted from the board and their values measured.
I’m posting this as a reference for members to consult. I’m not looking to start a dialog on the topic. In other words, I won’t be looking to answer any questions about it. I hope this effort is of some use to someone.
 [This message has been edited by PePe-LePu_For_2 (edited 05-12-2025).]
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richard in nc
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MAY 12, 05:58 PM
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which screws go to the oil guage?im trying to fix mine.i have the replacement board off ebay.
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pmbrunelle
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MAY 12, 06:38 PM
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| quote | Originally posted by richard in nc:
which screws go to the oil guage?im trying to fix mine.i have the replacement board off ebay. |
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OP said that his schematic is of an 88 GT tachometer, which has doesn't have an oil pressure gauge in the tachometer.
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phonedawgz
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MAY 12, 09:12 PM
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| quote | Originally posted by richard in nc:
which screws go to the oil guage?im trying to fix mine.i have the replacement board off ebay. |
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The bottom three open ones.
Not all tach boards are set up for oil pressure gauges. For example in many 84s there was a voltage gauge there, not an oil pressure gauge.
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phonedawgz
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MAY 12, 09:36 PM
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. [This message has been edited by phonedawgz (edited 05-12-2025).]
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Brian A
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MAY 13, 10:36 AM
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Very cool. Thank you for figuring this out and posting the schematic. It will be useful to someone sometime somewhere.
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fierosound
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MAY 13, 01:21 PM
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Patrick
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MAY 13, 04:06 PM
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Back in 2016, PFF member Chris Eddy was working on a prototype replacement tach board - Planning a universal tach PC board, and help with tachometer math
I took some photos and measurements at that time to try and assist Chris. Here's a couple of photos that may be of interest to anyone who might wish to poke around with their tachometers.
 [This message has been edited by Patrick (edited 05-13-2025).]
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Kitskaboodle
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MAY 13, 08:43 PM
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Patrick, just curious as to what year and engine the tach in your pic above is from? I noticed it has an oil pressure gauge built into the lower section of it. I do know that the tach in your pic is not from 86-88 GT cars. Kit [This message has been edited by Kitskaboodle (edited 05-13-2025).]
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Kitskaboodle
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MAY 13, 08:47 PM
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Patrick, just curious as to what year and engine the tach in your pic above is from? I noticed it has an oil pressure gauge built into the lower section of it. I do know that your pic is not from 86-88 GT cars. Kit
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