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[Jimw]

[video]https://m.youtube.com/watch?v=GIytNxPZ_SE[/video]



[video]https://m.youtube.com/watch?v=fgljMa0WDgU[/video]


So the wife got me a tach for Christmas. Figure this will be easy, four wires. Black for ground, red for power, white for light, green for signal. Instructions say to hook green to negative on coil. Hook it all up, light works but tach reading is not right. Check and double check that wires are correct and tight. Also double check that switch is set to eight cylinder. Still not right. Wife hears me bitching and sends it back and gets me a new one. Hook it up and same damm thing. Hook power and ground directly to battery. Light works but tach reading all over. Called previous owner and he never had a tach. I hook up my timing light to the negative on the coil and it reads rpm no problem. Everyone I talk to says I have it hooked up right. Don't know if it's a piece of Chinese crap or if I'm missing something. Any suggestions would be appreciated. See video of how tach reads and how timing light reads. Thanks

 

[Bruzilla]

Sounds like a bad ground.

 

[texas69bee]

x2 on the ground.

 

[furyus]

What ignition system do you have? Some don't work that way. My MSD has a specific tach connector on the box. Check with your ignition manufacturer.

 

[ws27]

Oops, some how I missed the sentence that said cylinder adjustment. Did you try to change the switch to one of the other settings just to see what happens. What do you have for an ignition system?

 

[Jimw]

Not sure about the ignition, just looks like a regular electronic ignition to me. I also thought it could be the ground. Hooked the ground wire directly to the battery. I checked the switch four times. tried it on 4, 6, and 8 cylinders

 

[Bruzilla]

When something electrical works, but doesn't work correctly, and acts that way for no discernible reason... 99% of the time you have a bad ground and power is getting bounced back into the unit and causing it's components to do stuff they were never intended to do.

 

[Jimw]

Ok so after returning the tach and getting a new one, then install new voltage regulator and ballast it still didn't work. Put a new ground on the alternator still no luck. Took it over my buddies house and tried it on his 69 GTX with a 440 and his 67 Charger with a 383. Hooked it to negative coil and it worked on both cars. Gave it one more try on my car hooking signal wire to negative on coil, did not work. I was just about ready to quit and throw the tach away. I thought what the hell, let me touch it to the positive on the coil. Figured I couldn't hurt it. Hook it up and the damm thing is working. Here is the coil and the green wire is hooked to positive. Took it for a ride and it works great. Hooked a volt meter to the + side and I have 3.8 volts. Hook to - side and I have 9.8.