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Wed Jul 04, 2012 1:55 pm

I just installed a Tachometer from HF
i hooked it up correctly, it is getting power and i connected it the negative side of the coil like it says too
when i start up the car it doesnt move, it lights up and has 12 volts going to it from the batery and AC but its not going anywhere when i rev it up.
From the negative side of the coil its showing im getting 7.5 volts.... is that showing my coil is going old???
should it be pulling 12 from the negative when its running?
THanks guys

Wed Jul 04, 2012 3:32 pm

You also have a ground wire connected, correct? There should be three wires: + - and coil negative terminal

Wed Jul 04, 2012 5:04 pm

ajbuggin8 wrote: I just installed a Tachometer from HF

Harbor Freight? there's your problem....CC, just like EMPI. :lol:

Wed Jul 04, 2012 7:08 pm

Is the tach for a 4 cylinder engine? Or, is it setup for 4 cylinder? I just installed one on another car (V8) and I noticed that out of the box it was setup for a V8, but there was a switch to set it for a 6 or 4 cylinder engines.

If I recall correctly, there were 3 leads on my tach:
1) positive, which was just for the backlight.
2) ground.
3) lead to the coil.

It should work without the (+) lead even connected. I think you could check the unit by just using the (-) and coil leads connected.

You might have the coil lead on the wrong side of the coil too.

Or, it might be a bad unit.

Wed Jul 04, 2012 8:09 pm

Typical wiring

Red to 12v must be connected
Black to ground must be connected
Green to coil neg {goes to points} must be connected
Coil neg will toggle 12v 0v 12v 0v when rinning

Getting a 7.5v reading, You may have an internal resistance coil on a car that requires an external res coil. How many volts do you have on the pos side?

Mon Jul 09, 2012 9:51 am

I connected the Red to the A/C the orange to the 12 Volt the black to ground the white to lights and the green to the negative side of the Coil
It is reading 7.5 Volts on the negative side of the coil.

Its just sitting still,
BTW, i buy alot of stuff at harbor freight and i gotta say i dont get why alot of people are so against it, its not the best quality stuff but i have had my air compressor and even my welder for years now and they work everytime without fail.
if i want a really good quality tool i go elsewhere but for a decent tool at a great price HF is the way to go imo i havent had anything fail yet from there and their return policy is awesome, this is the first fail i have had and im not sure if its my fault or the product....
thanks for the help guys

Mon Jul 09, 2012 9:53 am

dan macmillan wrote:

Getting a 7.5v reading, You may have an internal resistance coil on a car that requires an external res coil. How many volts do you have on the pos side?
I have 12 going in and 7.5 coming out, it is a blue coil, which looks like all the ones i have seen on VW's it is mounted to the fan housing.
could it be going out?

Mon Jul 09, 2012 11:38 am

I won't lie and say I haven't bought stuff at HF, some of my favorite tools I got there. Most of the other things they sell are akin to what you would buy at a carny sideshow, more to get your money than be useful.

Just remember that HF has lots of cheap tools, and some are just inexpensive. :lol:

Mon Jul 09, 2012 11:55 am

Steve22 wrote: I won't lie and say I haven't bought stuff at HF, some of my favorite tools I got there. Most of the other things they sell are akin to what you would buy at a carny sideshow, more to get your money than be useful.

Just remember that HF has lots of cheap tools, and some are just inexpensive. :lol:

agreed!
i think a big part is that i have gotten really lucky too haha

Mon Jul 09, 2012 12:04 pm

no photos , no joy,, sorry. try posting a photo. with cap off dizzy......

lets focus on the tech. not the HF boogy man.

first off 7.5v is failure

did you look at the points. are they even there. ? and not a Petronics
module in the place?
My mSD forbids using a tach on the coil , 500vdc signal there.. oops
and will blow up any tacho to hell.
the MSD has a dedicated gray tacho wire, that works perfectly.
MSD is a high end, CDI , ignition. see it?
http://ac-vw.com/My_Videos/spark%20test/msd/test.html

the points have only 2 voltages, 12v and 0v (repeats , hand cranked)
if you spin the motor real fast, the voltage will average. and go to 6v.

never in between. statically, or moving slow. (DC ranges)
but disconnect the tachometer and read that again.?

most tachs will work with points, does it state the in the manual?

step 1, set it for 4cylinder 4 cycles. RTM
step 2 wire it to 12vdc not to the ballast. Power wire.
step 3 wire the trigger wire (tacho input ) to the green points wire.
that green wire is called #1 in the DIN world. we call it in uSA MINUS lug.
step 4 ground the wire on the gage , marked ground. use a good ground.
step 5 , wire in the dial lamp to the parking lamp circuit.

that is it. step 5 , dont make it work , only glow in dark.

and we have no idea what you are driving, photo free. not at all.
40years of mods. are common.....