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Product # 3991

  • 3-3/8" (85.7mm)
  • Air-Core Air-Core
  • 0-8,000 RPM
  • Incandescent
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Since 1957, AutoMeter has set the standard in performance, accuracy and durability with their legendary Tachometers. The absolute pinnacle of engineering and technology, it’s no wonder AutoMeter can lay claim to more motorsports victories than every other gauge manufacturer combined. The patented air core meter movement, wound in house to exacting standards, can move the needle from 0 - 10,000 rpm in 333 milliseconds. An inaugural inductee to the Hot Rod Speed Parts Hall of Fame, no other tachometer on the market has had anything approaching its impact on professional racing. Built for a lifetime of service under the harshest conditions, this is the no compromise tach for no compromise builds. When you’re ready for the best, there isn’t another choice.

Feature Points

  • Traditional incandescent lighting illuminates around the perimeter of the dial
  • Compatible with most 4, 6, and 8 cylinder engines (2 - 4 pulse per revolution ignition signals) with points, electronic, and most 12V high-performance racing ignitions.
  • 12 and 16 volt compatible, well-suited with nearly every street car or race car electrical system
  • Gauge kit includes bulb and socket assembly, red and green bulb covers, mounting hardware, and detailed instructions for installation
  • AutoMeter’s race proven air-core electric tachometers provide quick and accurate readings with a needle so responsive it can go from 0 - full scale in 333 milliseconds

Bulb & Socket

  • 3212

Light Covers

  • Red 3214 & Green 3215

Mounting Hardware

  • Bracket Included
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I Want Use These On My CHEVY C10 Which Currently Has A LS SWAP. Will They Be Compatible With The Wiring ?

Asked by: Alex Q
Thank you for your question. While our tachs should certainly work with the Tach output from the LS computer, our gauges are not made to work with OEM wiring and we recommend wiring all our gauges separately from your OEM harness.
Answered by: Zach from AutoMeter
Date published: 2019-09-04

Is there a way to make this tach work on a1994 Harley fxrp.

Asked by: Cory Hatfield
Thank you for your inquiry, While this Sport Comp tach can calibrate correctly to one pulse per revolution, it is not designed for the weather exposure and vibration encountered with motorcycle use. We don't advise using it on a motorcycle.
Answered by: Jim from AutoMeter
Date published: 2019-08-16

Does this Tach require a special plug to be used with pigtails. Its to be on a indash 327 1967 camaro.

Asked by: Murphydog
Thank you for your inquiry. The 3991 can be installed using standard automotive hookup wire and female spade connectors. . This instrument has male spade connectors to attach your wires and female connectors to.
Answered by: Jim from AutoMeter
Date published: 2019-03-28

Is this tachometer compatible with a shift light?

Asked by: Hunter
Thank you for your question. This tachometer does not have a shift light output. If you wanted to use a shift light with it you would need to get either a shift light controller like our #5312 or a standalone shift light like #5343.
Answered by: Zach from AutoMeter
Date published: 2019-03-21

My tachometer, at around 3,000 rpm, begins flicking back and forth and then does not accurately measure the rpm's from that point. Can you help me with this problem?

Asked by: jhdumbolton
Thank you for your question. This sounds like something we will want to do some in depth troubleshooting with. I recommend you reach out to our support team and they would be happy to help you get this resolved. You can call them at 866.248.6357 or send them a contact request here https://www.autometer.com/contacts
Answered by: Zach from AutoMeter
Date published: 2019-01-15

Will this work with a 12A rotary with electronic distributor ignition?

Asked by: braap
Thank you for connecting with us. Our tachometers are compatible with the Mazda rotary engines. You'll need to set the tachometer for a 2 pulse per rev (ppr), which is more commonly associated with a 4 cylinder vehicle, then go to the negative side of the lead coil for the signal.
Answered by: Matt from AutoMeter
Date published: 2019-01-04

Recently order the Tachometer 105-3991.. I'm wanting to mount it on my Steering column mount for my 74 Bronco. It's required a 3 3/8" Tach and once I received my order, it reads 3 3/4" on the box. Is there a typo or is that the face size?

Asked by: Jase
Hi Jase, thank you for reaching out to us. The 3991 fits into a 3-3/8" diameter hole, but the bezel diameter is 3-3/4". We've tried to remain more consistent by referencing hole size on in-dash instruments, but may have some older label descriptions that reference the bezel diameter of 3-3/4".
Answered by: Matt from AutoMeter
Date published: 2018-08-25

The autometer 3991 tach does not come with standard lighting pigtail. How do I access the light to use the supplied bulb accessories (little rubber things to change the color of the light)?

Asked by: Darren
Hi Darren, thank you so much for contacting us. The socket is inside the housing of the tach itself. Simply pry off the black cover on the back of the tach and you can use a set of needle nose pliers to remove the socket inside. It's a 1/4 turn counterclockwise and it will come right out. Hope this helps!
Answered by: Joseph At AutoMeter
Date published: 2018-06-25
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