TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > Electrical - non engine
  New Posts New Posts RSS Feed - 70 AMX Tach with Electronic Ignition
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

70 AMX Tach with Electronic Ignition

 Post Reply Post Reply Page  <12
Author
Message
PHAT69AMX View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jul/07/2007
Location: West Virginia
Status: Offline
Points: 5903
Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Feb/15/2020 at 7:29pm
HEI will not work the original 1969 Tach, nor will any other "electronic" HAL Effect Distributor.
The stock AMC Tachometer is like an early Mustang, those are both 'Current Triggered'.
Understanding is the HEI, HAL Effect, Magnetic units are 'Voltage Triggered'.
Apples and oranges.
Something is needed to generate a 'Current Triggered' signal to run the stock tachometer
from the 'Voltage Triggered' signal generated by the HEI.
Back to Top
JerryB View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Dec/19/2018
Location: Aiken, SC
Status: Offline
Points: 38
Post Options Post Options   Thanks (0) Thanks(0)   Quote JerryB Quote  Post ReplyReply Direct Link To This Post Posted: Feb/16/2020 at 5:13am
I have sent my tach to the Tachman in Greer, SC. He is going to make it a "three-wire" tach to make it work. He is also lubing the speedometer and making sure it is calibrated. I should get it back in the next week or so. I'll have a better understanding then and I will give an update.
Back to Top
mbwicz View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum


Joined: Feb/20/2019
Location: Buffalo, NY
Status: Offline
Points: 1979
Post Options Post Options   Thanks (0) Thanks(0)   Quote mbwicz Quote  Post ReplyReply Direct Link To This Post Posted: Feb/16/2020 at 9:56am
I'm in the same boat, I just reached out to Tachman to update mine.  I've seen several threads where he does good work.  I look forward to your feedback.

Mike
1970 AMX, one step forward, one step back. Both steps cost time and money.
Back to Top
AMX2020 View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Feb/12/2020
Location: Canada
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote AMX2020 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/16/2020 at 11:04am
Looking at the Tachman website I see that they service the 69-74 AMX/Javelin tach. Is the 68 tach of a different design?
Back to Top
Ralph G. View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Apr/06/2016
Location: Cincinnati
Status: Offline
Points: 185
Post Options Post Options   Thanks (0) Thanks(0)   Quote Ralph G. Quote  Post ReplyReply Direct Link To This Post Posted: Feb/16/2020 at 11:09am
It's a different size than the '69 but the same basic design. Jeeps of the 1970's -80's used the same basic design as well. I believe Faria made the Jeep units.
Back to Top
bigbad69 View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Jul/02/2007
Location: Ottawa, Ont.
Status: Offline
Points: 6603
Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/16/2020 at 1:53pm
For the 69 AMX, the tach was combined with the 140 speedo. The 69 Javelin had the same smaller tach, fit in the clock pod, that the 68 AMX used. This was a dealer installed option for the Javelin.
69 Javelin SST BBO 390 T10
Back to Top
AMX2020 View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Feb/12/2020
Location: Canada
Status: Offline
Points: 81
Post Options Post Options   Thanks (0) Thanks(0)   Quote AMX2020 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/24/2020 at 7:32pm
So if I understand correctly, the Tachman can modify the OEM tach to work with voltage rather than current?

Also would the $100 device from MSD fix the issue (rather than sending to the Tachman) or is that device only relevant if you are using a MSD CD ignition box?

My AMX is using a GM large cap HEI, no MSD box. The car is wired using Ron Francis wiring. I can see the tach wire attached to the Tach output on the distributor. At this point I do not know if is connected to the tach itself (but I assume so) or whether the tach itself is non-functional. There is no light in the tach pod but it may not be related to the tach not working.
Back to Top
JerryB View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Dec/19/2018
Location: Aiken, SC
Status: Offline
Points: 38
Post Options Post Options   Thanks (0) Thanks(0)   Quote JerryB Quote  Post ReplyReply Direct Link To This Post Posted: Feb/25/2020 at 3:31am
Hopefully I will be able to answer some of your questions this weekend. Originally two wires came off the back of my tach. In the mix was a yellow resistance wire that was there to prevent my points from burning up in the OEM setup. The MSD won't work with my Ignitor 3 coil. I am not an electrical person, but I don't understand how it could run off voltage. I would think that would be constant. I am learning this stuff as I go along.
Back to Top
bigbad69 View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Jul/02/2007
Location: Ottawa, Ont.
Status: Offline
Points: 6603
Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/25/2020 at 8:24am
The voltage in the ignition primary circuit is not constant. The breaker points (or transistor in an electronic ignition) are constantly opening and closing the circuit. The negative terminal on the coil has a pulsating DC waveform. i.e it alternates between 12V (~9V if the resistance wire is in place) and 0V.

A voltage triggered tach senses those voltage transitions to calculate the engine RPM. 
69 Javelin SST BBO 390 T10
Back to Top
 Post Reply Post Reply Page  <12
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.109 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or