Tachometer


IHC in the early to mid-fifties.

Golden Jubilee
Golden Jubilee

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Post Tue Mar 18, 2014 7:28 pm

Tachometer

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
Attachments
my truck tach.jpg
my truck tach 2.jpg
my truck tach.jpg
1952 L-112 Long Bed BD220 3 speed, 4x4.
1962 Dodge Dart 330, 392 Hemi, T56 6 speed manual.
1986 GMC K1500 Jimmy, 396 V8, 700R4, 208C, 4x4.
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Golden Jubilee
Golden Jubilee

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Location: Saskatchewan

Post Tue Mar 18, 2014 8:13 pm

Re: Tachometer

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.

Pile of Parts
Pile of Parts

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Joined: Fri May 17, 2013 10:09 am

Post Tue Mar 18, 2014 9:04 pm

Re: Tachometer

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.

Golden Jubilee
Golden Jubilee

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Post Tue Mar 18, 2014 9:21 pm

Re: Tachometer

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?
1952 L-112 Long Bed BD220 3 speed, 4x4.
1962 Dodge Dart 330, 392 Hemi, T56 6 speed manual.
1986 GMC K1500 Jimmy, 396 V8, 700R4, 208C, 4x4.

Golden Jubilee
Golden Jubilee

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Location: Lyman, IA

Post Tue Mar 18, 2014 9:34 pm

Re: Tachometer

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.

Golden Jubilee
Golden Jubilee

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Post Tue Mar 18, 2014 9:44 pm

Re: Tachometer

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?
1952 L-112 Long Bed BD220 3 speed, 4x4.
1962 Dodge Dart 330, 392 Hemi, T56 6 speed manual.
1986 GMC K1500 Jimmy, 396 V8, 700R4, 208C, 4x4.

Pile of Parts
Pile of Parts

Posts: 39

Joined: Fri May 17, 2013 10:09 am

Post Tue Mar 18, 2014 10:21 pm

Re: Tachometer

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.

Golden Jubilee
Golden Jubilee

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Post Wed Mar 19, 2014 10:30 am

Re: Tachometer

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?
1952 L-112 Long Bed BD220 3 speed, 4x4.
1962 Dodge Dart 330, 392 Hemi, T56 6 speed manual.
1986 GMC K1500 Jimmy, 396 V8, 700R4, 208C, 4x4.

Rusty Driver
Rusty Driver

Posts: 186

Joined: Wed Dec 05, 2012 12:46 pm

Post Wed Mar 19, 2014 12:19 pm

Re: Tachometer

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.

Golden Jubilee
Golden Jubilee

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Location: Lyman, IA

Post Wed Mar 19, 2014 3:20 pm

Re: Tachometer

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.
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