Help with Digital Tachometer 4 Wires.

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I bought one of those cheap Digital Tachs aio that barely have instructions and have scoured the internet in hopes that i wasn't the only one just trying my luck with the damn thing. I have managed to get my Speedometer to work pretty accurately from getting a bicycle drive cable. Leaving me with the other 4 wires to hook up. Only problem is the gauge wants to see 12 v and the bike is high voltage Magneto Coil with a red and black for the whole setup on the cdi. Currently have been experimenting with it connected to the battery to see if i can get the other two wires (black/red and blue/white) to pick up the tach signal. but im worried that it not be properly grounded maybe? Due to battery being a seperate circuit its not seeing the tach from the magneto properly? I've tested both wires and i get a issue where the tachometer just glitches out when the bike is running like its short circuiting and quickly and repeatedly restarts itself, so i kill the bike and disconnect the wire leading to ground on spark. Things return to normal. However even if only connected via the battery i still see the gauge attempt to fade out on the lcd panel, flickering when driving at 30ish mph which i know the Mag is definitely putting its max voltage out. Mechanical drives create there own voltage im aware ti dectech your speed. and engine rpm is usually measured from the pulses the mag puts out. I have no clue exactly what this gauge is detecting due to lack of available info on the gauge itself. I Just want some help figuring this out because i have a strong feeling it can work given right tools and parts. Just now thinking about it i wonder if the battery is attempting to complete the circuit from the drive cable grounding itself?


My hand to mouse drawing skills suck but here's a diagram.

And here's a link to the gauge.

https://www.amazon.com/gp/product/B08J46VSFF/ref=ppx_yo_dt_b_asin_title_o04_s01?ie=UTF8&psc=1
 

Chainlube

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The way I take it, the green goes to neg on battery the black to plus and the b/w to the white wire on the bike engine. Ignore the b/r wire.

HTH.
 

DieselTech

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Green to ground(-)
Black to positive (+)
Blue & white (SPD)is speed signal, Idk but i dont think you want the speed signal wire on the white mag wire, because it's a voltage wire. I think your speed signal wire needs to be tied into the black wire on the coil. If it dont work on the black coil wire it needs tied into the red coil wire. The speed signal wire needs a signal that makes & breaks circuit.
Brown & red (fuel level)=not used. This is my take on that tach gauge on how to wire it,
 

Mossy

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An induction tach is what I would use... One wire that clamps around the plug wire...
 

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I failed to make a ac to dc converter for the 12v battery i have attached, maybe its the diode i used, i had salvaged a old smps i had laying around so who knows why that failed. I'll try switching the Blue/white wire to the coils ground (black) and see what happens, when this rain in my area stops i will post the results.. I'm still hoping its not wanting to see the battery connected to magneto to work. Still waiting to get paid to buy a real voltage regulator to connect battery to Magneto.
 

Mossy

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I failed to make a ac to dc converter for the 12v battery i have attached, maybe its the diode i used, i had salvaged a old smps i had laying around so who knows why that failed. I'll try switching the Blue/white wire to the coils ground (black) and see what happens, when this rain in my area stops i will post the results.. I'm still hoping its not wanting to see the battery connected to magneto to work. Still waiting to get paid to buy a real voltage regulator to connect battery to Magneto.
There's this... Few of us recently been discussing electrical charging 2 and 4 stroke... Few threads about it
 

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Local time
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Ok so new things have happened recently. I did connect blue/white to the black coil and it robbed all my spark from the coil so in my need to get to work i did not attempt to mess with it any more and disconnected blue/white wire for time being. Went ahead and ordered a voltage regulator online to hopefully get past this mess. Its a 4 wire Rectifier, regulator. Now this being said, is this blue/white wire from the tach going to connect to the voltage regulator? Or is that still going to block the proper pulses? The only reason im not willing to get another tach is i dont want a million wires running down to my motor and this tach already has all the functions minus a temp gauge

Voltage Makeithappener on Jungle Web.
 

Mossy

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An induction tach is what I would use... One wire that clamps around the plug wire...
Ok so new things have happened recently. I did connect blue/white to the black coil and it robbed all my spark from the coil so in my need to get to work i did not attempt to mess with it any more and disconnected blue/white wire for time being. Went ahead and ordered a voltage regulator online to hopefully get past this mess. Its a 4 wire Rectifier, regulator. Now this being said, is this blue/white wire from the tach going to connect to the voltage regulator? Or is that still going to block the proper pulses? The only reason im not willing to get another tach is i dont want a million wires running down to my motor and this tach already has all the functions minus a temp gauge

Voltage Makeithappener on Jungle Web.
This is going to be the best way other than useing the extra mag type...ton of wires.. You don't want to connect anything to the sparker mag searching for a signal on 12V AC and a milliamp of power...
 
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