4 replies to this topic

[allsop61]

1993 italian job  
 
Hi, just nearing the end of my restoration, only thing that does not work is the Tachometer
not sure if it worked before as it was a non runner when i bought it.
 
I have battery voltage at the Green/Orange wire to the Tacho with engine running
the white and black wire at the Tacho reads zero
 
With the engine running if I run a wire from the - terminal  of the coil to where the black/white  wire goes to at the back of the Tacho
and only just or very slightly touch the terminal  the Tacho springs into life, but if I hold it firmly on the terminal the Tacho dies again 
any help would be appreciated thanks 
 
ps i don't know if this would affect it but i'm waiting for a new coil to arrive as the one fitted is a 1.5 ohms sports coil but I have full battery voltage at the positive feed of the coil ( only 1 wire at the + side of coil, no extra wire from the starter solenoid )    

Edited by allsop61, 02 January 2016 - 05:35 PM.

[RHDmini74]

I had the same problem when the wire was on the + side of the coil. When I connected it to the - side it works. Maybe try connecting it to the - side?

[allsop61]

Hi, I have one feed wire to the + side of coil and 2 wires from the distributor to the - side of the coil, thanks 

[dklawson]

Before you fit that new coil, how did you measure the voltage?  To determine the coil type required the coil MUST have an earth connection on coil (-).  To do this, connect a jumper wire between coil (-) and earth.  This simulates the points being closed.  Now switch the ignition on and measure the voltage between coil (+) and earth.  If you measure 6V to 9V, you need a ballast coil.  If you measure 12V, you need a standard coil.  Again, the coil MUST have an earth connection during voltage tests to create the voltage drop that will indicate what type of coil your car is wired for.

 

Returning to the tach, make sure your earth connections at the gauge cluster are clean and tight.  You will NOT be able to measure a constant voltage on the white/black wire.  With the engine running the voltage on white/black will be bouncing between 0V and 14V.  If you have a digital meter, the reading will be changing all the time.  If you have an analog meter, the needle will flutter at some voltage... probably around 5V.

 

I cannot explain why firmly pushing your test wire against the tach causes the tach to stop working.  That suggests a damaged circuit board that might be flexing.  Perhaps inspect all the tach connections and any flex circuits for cracks.

 

Take the following as a light hearted comment as your post made me smile.  This is not a barb or flame.

You are dealing with a rev counter, tachometer, tach, or tacho (for short).  A "taco" is something you eat.

 

 

Tachometer (tach, tacho)

 

 

 

Taco

[allsop61]

Haha silly me, thanks for pointing that out, made me laugh and thanks for your help Doug

Edited by allsop61, 02 January 2016 - 04:02 PM.