I just wanted to know if the tach works without the orange hot wire hooked up. I wasn't going to use the clock to save battery. Thanks

 

All the orange wire does is power the clock.

The clock will run for months before discharging the battery. If the car sits long enough for the clock to discharge the battery, you probably should unhook the battery cables anyway. Another option is to put a small (2-3 amp would be plenty) fuse on the orange wire to the clock. Instead of leaving the wire off (which means the clock will never work) you could pull the fuse and disable power to the clock.

 

As Matt says, the clock is a minor battery drain. The larger problem is that voltage from a neglected battery eventually falls low enough that when the points close to wind the clock, there's not enough voltage. The points stay shut and the constant current toasts the electromagnet or fuses the points.

Best to disconnect the clock if you are not maintaining the battery.

 

ok thanks. I used a standard wire from tach to distributer but tach didn't work. Do I need to use a special wire?

 

Standard wire for the tach is all that is needed. It’s such a small amount of current 18 gauge wire would be plenty big enough.

 

Doesn’t a tachometer need 3 connections: power, ground, and trigger signal?

 

The gauge gets its ground thru the mounting tabs to the dash.

 

OK, so doesn't the tach also need +12 Volts, as in the orange wire?

 

I will check it with the orange wire. Thanks

 

The clock needs a constant 12 bolts to keep the clock running. The tach only needs a ground they the mounting tabs and a signal from the coil. That’s it, nothing else needed.

Well, the illumination lamps needs a power source from the dash lamp circuit (gray wire) they are also grounded thru the mounting tabs.

 

All of the tachometer wiring diagrams I find show a +12 Volt connection in addition to the trigger and ground (and illumination). This is also what I remember from installing a Sun Super Tach in my car.

https://images.carid.com/bosch/custo...nstruction.pdf

Is it possible the BATT connection in the images above is shared between the clock and the tach for simplicity of connecting it to the vehicle's wiring harness?

 

Ok, so the tach that I bought from the parts place on ebay, sits at 3500 when eng is off. Then when it starts it goes to 4500 to 5000. How do you fix the calibration? I did need the orange hot wire to make it work also. I did send an email to thepartsplace also.