Not that it matters but this is it ::
http://m.alibaba.com/product/331008894/5_4_in_1_digital_auto/specifications.html

would it be a good idea to use the fuse box for power supply?

Folks I have run into the WIERDEST problem I have ever experienced .. 

I found the power supply to hook the TACH to.. temporarily.. in the fuse box, on a fuse for accessory that turns on with the switch.. 

Ok... So , i connect the tach up, and start the car, and the tach goes to 2000 and sticks there.. and then as I would give gas to the car, it would just keep rising.. until it would max out, and my engine is actually ideling. .. Its Like its got an issue somehow. ok .. Starting to troubleshoot the best I know.: 

1) Use the positive instead of the negative on the coil to see if it makes a difference : NO

2) Disconnect everything take the tach to the engine bay, go straight to the battery red to red black to black and green to the positive terminal of the coil (just to check)--- NO

3) Use the negative of the coil : Woalla!! Tach is on and following rpm like its supposed to. everything looks good.

4) Now that is interesting.. what was wrong inside the cabin.. Ok.. may be becuase my TACH input is running to my remote security and remote start box, may be tach doesnt like the current drop because of the splice... Lets take another wire and run it straight from the coil to inside the cabin and try :::::::::::::::::::::::::: NO!!!!!! same freaking tach rising higher and higher slowly till it maxes and stayes there..

5) OK BAD GROUND: MAY be he body isnt grounded well enough , so run another long wire from the battery's negative terminal all the way to inside the cabin.. cant get a better ground than from the battery itself.. NOPE! @__@ !! Why does this hate me? LOL

------So the only thing left to do that I might try is to power the sucker from the battery straight and use the spliced signal wire I have inside the cabin to read the tach readings. 

QUESTION: Why is this happening. Why does the tach works straight off the battery in the engine compartment.. but CONSISTENTLY does not in the cabin.. I am a little frustrated. Its a Tach for crying out loud! how hard can it be? ? ? ?? 


By the way I found the NPT adapters for the oil and temp electronic sensors at NAPA.. but only will it work after the stupid tach decides to freaking work!!!!!  

I am an electrical engineer.. and a tach is defeating me.. HELP! 

 I am positive that it is on the negative terminal :D 

why i say this is because, I double triple checked.. I am running petronix points and a flmae thrower coil.. hope that doenst make a difference.. 

Like you said it wont work or wont work right on the positive, that is true as even in the engine bay it didnt work.. but in the cabin is where its powered off a port on the fuse box.. (even if grounded) straight to battery, it doenst work.. or it "acts like a voltmeter"

Michael H. wrote:

Sorry... I wasn't trying to insult your intelligence... just making sure.

The pertonix shouldn't matter...I am running a pertronix II and flamethrower II coil and my tach works fine.

ohh not at all... Its a good point.. and yes small things can be missed..

amkes me want to install a new fuse block in there getting power straight from the battery with a relay activating power to it.. Anything you know thats a fuse box with a built in relay like that? I am just asking becasue it will be prettier .. to install with a relay already in there, rather than having a relay installed seperately somewhere. Please let me know. 

how i know that its 12 volts is that this tach has a voltage meter in it.. Its tell me what its getting (one of the 4in1 things) .. So that would be somewhere from 12.1-12.8 when car is off.. ranging up to 14.1 with the car on (on alternator) .. 

I did actually, if you notice, run a seperate wire from coil to the tach to make sure that the remote start was in no way interferring with the TACH.. no bueno

and i notice you said to disconnet it completely from tach.. that was an interation I did too.. I removed the remote start TACH signal and left just the new wire on the coil, accidentally actually.. and that gave no good results either.  

But in the engine bay with this tach.. the coil had the remote start wire hooked on to it, and the tach was working with it on.. CONFUSION CONFUSION lol

Last edited by Gaba (3/13/2014 11:06 AM)

I'll try to get to that.. with the underdash AC , its a bit crowded up in there. and I dont like to pull on things, as you never know what old wiring will fall apart.. any way of getting to it from the front.. 

again remember NOOBIE here :D 

No way to get to it from the front, unless you pull the switch which is more trouble than it's worth.   You can probably do it all by feel.  Reach up to behind the switch and feel for the stud.   I forgot the thread size but if you have a eyelet on the end of the red wire you might be able to get it on the stud and tighten with a suitable nut.

Sounds like a hostile tachover to me...

wsinsle wrote:

If holy water doesn't work I guarantee a 3 pound hammer will.

lmao... !! good to know.. I just bought one too!! hahahahahhah will "break it in " :D