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1969 AMX Tach - Driving me crazy

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Greyhounds_AMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jun/23/2018 at 9:38am
Is that Adrian in Berlin?
1968 AMX 390 w/T5
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jun/28/2018 at 11:36am
I've been wanting to build a hidden shift light for my AMX for a while, maybe it'd would be a good idea to build a replacement tach circuit as well so we can run an MSD without the silly noisey 8920 tach adapter. I've been wanting to fix or dump that thing for 17 years now.

The spare tach I have appears to be fried though so I've got to dig around a bit for another to prototype with. 

The 69 tach that I have apart has an internal PCB with plug in leads going to the meter movement, so I'm thinking it would make the most sense to build a new board that would drop in the casing. It would need three connections though, so instead of stud connections out the back we'd end up with positive, negative, and tach wires coming out from the two original stud holes. The positive and negative are available right on the instrument cluster though, so that'd be easy. In fact we'd probably have all three wires come out one hole and line a calibration pot up with the other hole so it could be adjusted with a small screwdriver.

musictoyz, can you measure the resistance across your movement? It should just unplug from the PCB.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jun/28/2018 at 12:18pm
Speaking of Hidden Shift Lights....
The 68-9 AMX Emergency Brake Warning Light, ~3/4 dia Red Lens, front and center of dash pod,
is a stand alone 2-wire incandescent bulb rubber / plastic 1/4 turn board mounted bulb holder...
That was my Hidden Shift Light... activated by an MSD RPM Activated Switch, used RPM "Pills"
which I already had to change at what RPM the Light came on, wired a Toggle Switch in-line
hidden underdash to Activate & Deactivate the new incognito Shift Light... 


Edited by PHAT69AMX - Jun/28/2018 at 3:19pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty 401 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/28/2018 at 2:03pm
how did you wire it to be a shift light ? 

72 matador 401 the beast
79 concord 2 door
72 matador 304 grasshopper
68 Rogue 406
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jun/28/2018 at 3:15pm
It is a stand alone 2-wire Bulb and socket, factory bullet Connectors on short leads, unplugged the 2 factory Emergency Brake Switch wires, got an MSD RPM Activated Switch, already had MSD rpm "pills", wired the MSD RPM Activated Switch to turn on the old original in dash center located "hidden" Emergency Brake Warning Light...  Change "pills" to change when light comes on... wired a hidden underdash toggle switch in-line to enable and disable the new "incognito" shift light...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2018 at 9:07am
Here's what my 68 tach movement measures. Note that the little bit of current from the ohmmeter is driving the tach. The original Faria tach patent that these are based on used a 1 mA meter.

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