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Tachometer
Posted:
Tue Mar 18, 2014 7:28 pmby Ethan
ok so according to my new Sunpro Super Tach II when i run my truck im barely at 2000 RPMs nowhere near redlining it when shifting, and the directions said hook it up to the negative on the coil but it only works when hooked to the positive, either my engine is just really loud at 2100 RPMs or somethings wrong but other then that everything is hooked up correctly with an extremely good ground and yes its a universal tach set to 6 cylinder mode
Re: Tachometer
Posted:
Tue Mar 18, 2014 8:13 pmby Ralph Goff
I had a tach on my B110 years ago but can't recall where I connected it . Seems like it might have been right at the distributor. Also the tach I had needed an internal setting changed depending if it was on a 4, 6 or 8 cylinder engine.
Re: Tachometer
Posted:
Tue Mar 18, 2014 9:04 pmby IHkruzer
The directions are for a negative-ground vehicle. A tachometer should be hooked to the terminal that is connected to the ignition points, because your tach is actually measuring how often your points are opening and closing. By the photos, it appears your pickup is positive-ground. On a negative-ground vehicle, the coil's negative post should be hooked to the points. On a positive ground vehicle, the plus terminal of the coil should be hooked to the points.
The directions that the manufacturer gave you just ASSUMED that your vehicle was negative ground.
Now the big questions is if the tachometer is accurate on a positive-grounded vehicle.
Re: Tachometer
Posted:
Tue Mar 18, 2014 9:21 pmby Ethan
the guy before me converted to 12 volt negative, do you think he just forgot the coil? and if so then that means i have direct power running to the negative post on the coil, isnt that bad? do i need to get a new coil for the system?
Re: Tachometer
Posted:
Tue Mar 18, 2014 9:34 pmby cornbinder89
No, just swap the leads. The terminal that goes to the points, should be the same polarity as the battery, - for -ground + for +ground.
BTW if he didn't change the coil, you need a 12 volt coil.
Re: Tachometer
Posted:
Tue Mar 18, 2014 9:44 pmby Ethan
cornbinder89 wrote:No, just swap the leads. The terminal that goes to the points, should be the same polarity as the battery, - for -ground + for +ground.
BTW if he didn't change the coil, you need a 12 volt coil.
You mean like hook the distributer to the negative post and the direct power to the positive post on the coil?
Re: Tachometer
Posted:
Tue Mar 18, 2014 10:21 pmby IHkruzer
Ethan wrote:You mean like hook the distributer to the negative post and the direct power to the positive post on the coil?
Yes, but when running 12 volts, the "direct power" should have a ballast resister between your ignition key and the plus (+) terminal of the coil and, as posted, make sure you have the correct coil.
Re: Tachometer
Posted:
Wed Mar 19, 2014 10:30 amby Ethan
IHkruzer wrote:Ethan wrote:You mean like hook the distributer to the negative post and the direct power to the positive post on the coil?
Yes, but when running 12 volts, the "direct power" should have a ballast resister between your ignition key and the plus (+) terminal of the coil and, as posted, make sure you have the correct coil.
How do i hook up a resistor, can i run the truck without it a couple times?
Re: Tachometer
Posted:
Wed Mar 19, 2014 12:19 pmby diltonw
Unless its worn off, there's a good chance your coil is labeled 6 or 12 volt. Since you need to turn it around to get the +/- right, you can give it a good looking over. The tricky thing is determining if you need a resister or not. Some coils have an internal resister, some need external (someone more knowledgeable may correct me here).
As far as accuracy of your tach, do you have a timing light? I think mine gives timing degrees and engine speed. If not you can probably borrow a timing light or engine analyzer from an auto parts store.
Re: Tachometer
Posted:
Wed Mar 19, 2014 3:20 pmby cornbinder89
Most 6 volt coils are used without a ballast. 12 volt coils can be internally ballasted (no external resistor required) or externally ballested (extenal resistor required). In most cases the voltage and whether it requires an external ballast will be stenciled on the coil but that could be missing by now. You can look up the part number if that is on the coil it will tell if a resistor is required.
If you are going to buy a new coil, internal ballasted is the easyest, just wire in place of the orignal 6 volt.