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).]
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).]
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).]
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
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
Patrick, just curious as to what year and engine the tach in your pic above is from?
Kit, I have so much Fiero stuff here that I have no idea where/what this tach was originally from. Judging from the red line, it would not have been a duke. So it would've been from a V6 Fiero that did not have a center console gauge cluster. Possibly an '85 GT?
[EDIT] I just noticed this post...
quote
Originally posted by pmbrunelle:
That’s an 85 V6 tachometer, either SE or GT.
[This message has been edited by Patrick (edited 05-13-2025).]
Tony, judging from the discussion in This thread, I believe Chris moved on from the project... although he did say that one of the boards was of his design.
Thanks Patrick. Ironically, my silver Fiero is an 85 GT. However, the cluster swap and aux. gauge pkg. was one of the first things I did when I got the car. I do remember that the original one had the 85 mph speedo but I don’t remember (when I swapped it out) that it had an oil gauge at the bottom. Now that I think about it, I probably have the 85 cluster stashed in my garage. I just forgot about it. 😊 Kit
I did have a project some years ago for a replacement tach that could do oil or not, it used a Microchip PIC to drive the movement. If someone has experience with embedded programming and electronics, I would transfer what I have to you to take over.. please contact direct, I do not get on the board very often any more. ceddy@nb.net.
