Standard Ignition Coil
If you have a standard ignition coil you can use the negative terminal of the coil for the signal source. Use the SIG 2 (In-Dash Tach) or green wire (Pedestal Mount Tach) input (see "Signal Hookup" in the instructions). If you have a high output capacitive energy discharge type coil it is recommended that you install a tachometer filter to prevent damage to the tachometer.
If you have an ignition box (i.e. MSD 6AL) you can use the "Tach Output" from the ignition box. Use the SIG 1 (In-Dash Tach) or purple wire (Pedestal Mount Tach) input (see "Signal Hookup" in the instructions).
12V ECU Tachometer Signal
If you have a modern ignition system and your ECU (computer) has a dedicated 12V tachometer signal output you can use this to drive the tachometer. Use the SIG 1 (In-Dash Tach) or purple wire (Pedestal Mount Tach) input (see "Signal Hookup" in the instructions).
5V ECU Tachometer Signal
Some ECU outputs are 5V which will not drive the tachometer without modification. If you have a 5V Tachometer signal you can:
- Install a 1000 ohm "pull up" resister from the 12V gauge power source (ACC) to the signal wire to increase the signal strength.
- Contact us to special order a tachometer that will work with the 5V ECU signal.
- Install a Tach Driver (see "Coil Pack or Individual Coils" below).
If you have an HEI distributor with a "Tach Output" you can use the "Tach Output" from the distributor. Due to the high voltage of the signal from the HEI you should use a tachometer filter to prevent damage to the tachometer.
Coil Pack or Individual Coils (Distributorless Ignitions)
If you have a modern vehicle with "coil pack" or "individual ignition coils" distributorless igntion you will need a tach driver like the MSD 8913 to drive the tachometer. Connect the signal from the tach driver to SIG 1 (In-Dash Tach) or purple wire (Pedestal Mount Tach) input.
If your tachometer has no signal or an erratic signal (pointer jumping all over) you first need to verify that you have correct power, ground and signal connections.
- Verify the gauge has 12V power. The gauge should perform a self calibration check when turned on (pointer moves to full scale, then back to zero).
- Verify you have a good common ground. A bad ground connection is often the cause of many gauge issues. Make sure the gauge ground connection is connected directly to a good ground on the vehicle chassis. We recommend using the same location as the battery negative terminal ground.
- Verify you are using a proper signal source. The most common locations for a tach signal are the negative terminal of the ignition coil or tachometer output terminal (HEI, Ignition Control Boxes or ECU).
No Pointer Movement
- Verify 12V ACC, signal and ground connections (see above).
- Verify you have a good signal that is at least 8V peak to peak in amplitude (requires an oscilloscope). Some ECU signals are not strong enough to drive the tachometer.
- Try switching the signal input. Marshall tachometers come with 2 signal input options.
Erratic Pointer Movement
Back to FAQs
- Verify correct signal and ground connections (see above).
- Verify your signal wire is not routed close to any high voltage sources (i.e. spark plug wires, distributor). The signal wire can pick up electrical interference (signal noise) if routed close to a high voltage source.
- Try switching the signal input. Marshall tachometers come with 2 signal input options, each input utilizes a different signal filter.
- Add a 10K Ohm resister inline with the signal. Adding a resister will increase the level of signal filtering. Try this on both signal inputs. Use a higher ohm resister for more filtering, a lower value ohm resister for less filtering.
- Install a tachometer signal filter.
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