Umair Gaines
Harley-Davidson motorcycles are known for their powerful engines and iconic design. While these bikes offer an unparalleled riding experience, they also require regular maintenance and care to keep them in optimal condition. One essential aspect of Harley-Davidson maintenance is ensuring the accuracy of the tachometer, a critical instrument that measures engine revolutions per minute (RPM). In this discussion, we will delve into the methods and challenges of testing and calibrating the electric tachometer on a Harley-Davidson motorcycle, exploring solutions to common issues faced by riders and enthusiasts alike.
| Characteristics | Values |
|---|---|
| Tachometer function | Gauge engine RPM |
| Tachometer use | Critical to keep from redlining your motor |
| Speedometer function | Combination speedometer/tachometer |
| Speedometer use | Verify speedometer replacement |
| Fuel level display | Tank-mounted fuel gauge |
| Tachometer display | Tachometer pointer |
| Tachometer test | Use an oscilloscope |
| Harley models | 2008 Softail Rocker (FXCW) |
| Harley wires | Red (pos), Black (neg) & pink (signal) |
| Harley wire connection | Positive to the lights fuse and pink to the coil front cylinder |
| Harley wire colours | Pink, blue/orange |
| Harley voltage | 12.5 volts on the orange wire |
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What You'll Learn
- A cheap oscilloscope and a DIY function generator kit may be used to test the tachometer
- The tachometer's wires should be checked for correct installation
- The tachometer's wires should be checked for corrosion
- The tachometer's fuel level indicator may need to be checked
- The tachometer's compatibility with the bike's model should be checked
A cheap oscilloscope and a DIY function generator kit may be used to test the tachometer
The first step in testing the tachometer is to connect the oscilloscope to the generator's output and look for any repetitive waveform or spike. If there is a repetitive waveform, you can calculate the turns per second by dividing the frequency by the period. To get turns per minute, simply multiply this number by 60.
The function generator can then be used to create high-frequency pulses, which can be used to test the ignition's tach signal. This will allow you to see if the speed sensor is sending inconsistent signals.
It is important to note that a typical tachometer signal is not true AC voltage but pulsed DC voltage. Therefore, when using a multimeter to test the tachometer, it is necessary to use the AC voltage setting. Connect the negative meter lead to a chassis ground and the positive lead to the tachometer wire. Start the vehicle and wait for it to idle down to normal idle speed. The meter should now display a fairly constant AC voltage. If it does, rev the motor up and down and observe the reading. The AC voltage should rise and fall along with the engine RPM.
Additionally, when testing a tachometer, it is important to avoid using methods such as a test light, as this can cause damage to the vehicle.
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The tachometer's wires should be checked for correct installation
The correct installation of tachometer wires is essential for the proper functioning of your Harley. When installing a tachometer, it's important to refer to the service manual for your specific Harley model, as the wiring configuration may vary. In some cases, a Harley tachometer may come with three wires: a red positive wire, a black negative wire, and a pink signal wire. However, other models might use a seven-wire configuration.
When checking the wires, it is important to verify that they are securely connected to the appropriate components. For example, in some cases, the positive wire should be attached to the lights fuse, while the signal wire (which may be pink) should be connected to the coil of the front cylinder. Referring to the service manual or seeking guidance from a Harley dealership can help ensure that the wires are connected correctly.
In addition, it is important to consider the compatibility of the tachometer with your Harley's ignition system. Some Harley models use a single-fire ignition system, while others may have a dual-fire setup. Ensuring that your tachometer is compatible with your ignition system is crucial for accurate readings and the overall performance of your bike.
If you encounter issues during installation or if the tachometer doesn't work as expected, it's important to troubleshoot the wiring. Double-checking the connections, referring to the correct wiring diagram for your model, and ensuring there is no damage to the wires can help identify and resolve any problems.
Lastly, it is worth noting that some Harley owners have reported challenges with installing aftermarket tachometers, especially when trying to adapt them to the existing wiring harness. In some cases, purchasing a Harley-specific tachometer with the correct plugs and harness may be a more straightforward solution, even if it is more expensive.
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The tachometer's wires should be checked for corrosion
To test an electric tachometer on a Harley, it is important to check the tachometer wires for corrosion. Corrosion on the wires can cause issues with the tachometer's functionality and accuracy.
In one instance, a Harley owner experienced an issue with their bike immediately shutting off when they connected the pink cable, which is the signal wire, according to the service manual. They found that disconnecting the pink cable allowed the bike to start normally. This issue could be potentially attributed to wire corrosion, as it affects the signal transmission.
Another Harley owner encountered a problem with their tachometer installation, where the tach harness was wired incorrectly, leading to a blown ABS module. This issue may also be related to wire corrosion, as it can cause electrical faults and short circuits.
Furthermore, in a discussion on Harley-Davidson forums, a user reported getting 11 volts on the orange wires and 0.14 ohms on the ground wire, indicating potential wire corrosion. The user was advised to check the ground wire from the engine to the frame for corrosion and replace the wire if necessary.
To summarise, when testing and installing a Harley tachometer, it is crucial to inspect the wires for any signs of corrosion. Corroded wires can lead to inaccurate readings, electrical faults, and even damage to other components. Regular inspection and maintenance of the tachometer wires can help prevent these issues and ensure the proper functioning of the tachometer.
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The tachometer's fuel level indicator may need to be checked
The tachometers fuel level indicator may need to be checked if the fuel level display and tank-mounted fuel gauge do not match. The tank fuel gauge on a Harley-Davidson uses a continuous sweep needle to indicate fuel level, while the tachometer fuel level uses a segmented display, with each segment representing 1/8 of a tank. Therefore, if the fuel level display shows no change, but the needle on the tank-mounted gauge indicates a change in position, the fuel level indicator may need to be checked.
Additionally, if the fuel level indicator bars are stuck in the middle, even with a full tank, this could indicate an issue with the fuel level indicator. In this case, it is recommended to check the resistance range with a VOM, as the electrical diagnostics manual should have the correct range for your bike.
It is also important to note that the fuel display may not update immediately after the vehicle is put in motion. Instead, it may slowly update over the next 30 miles. Pressing and holding the "Trip" reset switch can help toggle between the "mile" and "kilo" displays.
If the fuel level indicator is still not functioning properly, it may be necessary to consult a Harley-Davidson dealer or a professional mechanic for further diagnostics and repair.
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The tachometer's compatibility with the bike's model should be checked
When it comes to testing an electric tachometer on a Harley, it is important to ensure that the tachometer is compatible with the specific bike model. Incompatibility may result in incorrect readings or even damage to the bike's electrical system.
Firstly, refer to the Harley-Davidson service manual for your bike's model and year. This manual should provide specific instructions and specifications for testing and installing the tachometer. Contact your local Harley-Davidson dealer to obtain the correct service manual if you do not already have access to it.
Secondly, check the specifications of the ignition system. As the ignition is often made by an aftermarket company, refer to their specifications for the output of the tach wire. This information will be crucial in determining compatibility with the tachometer.
Additionally, consider the type of speedometer your bike uses, whether it is mechanical or digital. A mechanical speedometer connects to the front wheel with a cable, while a digital speedometer uses a magnetic sensor. The compatibility of the tachometer may depend on the type of speedometer installed on the bike.
Furthermore, some speedometers may be designed to fit a wide range of bikes, but it is always advisable to verify their compatibility with your specific bike model. Refer to the product descriptions and installation instructions provided by the manufacturer to ensure the tachometer is suitable for your Harley.
By carefully considering these factors and referring to the appropriate resources, you can ensure that the electric tachometer is compatible with your Harley's model, thus avoiding potential issues and ensuring accurate readings.
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Frequently asked questions
You will need an oscilloscope and a DIY function generator kit.
First, pull the sending unit and check the resistance range with a VOM. You can find the correct range for your bike in your electrical diagnostics manual.
You will need to connect the positive to the lights fuse and the signal wire to the coil front cylinder.
