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Short Sweep Electric Crash Course
A Short Sweep Electric (SSE) or Air-Core gauge is at its essence, a small magnetic core with copper windings around it that will move in relationship to the voltage it sees. This is regulated by an electronic sending unit, which will change its resistance to ground based on the reading. As a temperature or pressure changes, the resistance the gauge measures and thereby the voltage the air core sees varies dictating that the indicator moves to a calibrated position on the dial. As one of the most popular gauge types, here are some common mishaps and fixes:
My SSE oil pressure and water temperature gauge are reading too high, and getting there too quickly.
Sometimes with this symptom, it will read pressure merely by turning the power on, or read temperature before the engine has even been started. This would be most often, the loose or missing nut on the ground terminal, on the rear of the gauge. The next most common is using poor or insufficient ground for the gauge. After that, check for an incorrect, or faulty sender.
SSE pressure and temperature have no reading.
Assuming the gauge power and ground are proven good, attach a jumper wire from the end of the sender wire (at the sender), and the other end to ground. The gauge should deflect to full-scale reading. If it does, then check to make sure the sender is threaded into something grounded. For example, threading into an adapter, teed into a rubber hose requires the adapter to be grounded.
SSE pressure and temperature have no reading, it fails above grounding of the sender wire test.
For this, try shunting the “S” terminal direct to the “GND” terminal at the rear of the gauge (instead of grounding the sender wire under the hood). If it now deflects to full scale, then the sender wire is open circuited or has a bad connection at some point. If the gauge still does not go to full deflection, then simply measure across the “I” and “GND terminals to check for proper power & ground.
SSE pressure and temperature are reading, but too low.
This too can be related to poor grounding of the sender. Try cleaning off excess sealant from threads and make sure what the sender is threaded into is sufficiently grounded. Also, make sure the proper sender is being used.
The SSE, 0-90, 16-158, 0-30 ohm fuel level goes past full.
The number one cause is a non-grounded sender in the tank. Run a grounded wire to the mounting flange of the sender. The second most common cause is an improper sender being used for gauge resistance range. Verify resistance of the sender at empty and full, and the model number of the gauge. The third most common cause is an incomplete circuit between “S” terminal of gauge, and the terminal of the sender. You may try a new length of wire from gauge to the sender. You can always check for gauge ability to operate properly by running sender wire directly to ground as a test. If the gauge goes to empty or below by doing this, then the gauge is most likely not the problem.
The voltmeter reads low.
Verify the voltmeter reading by using a handheld multimeter and compare the reading directly at the back of the gauge. Most often, this matches what the gauge is seeing. This would mean that either overall system voltage really is low or the voltage is low due to a high resistance connection on either the power or ground side. Comparing interior volt meters to the reading at the battery is not a good comparison, as interior voltage can commonly be 0.5 to 2.0 volts lower than the battery voltage (ideally 1.0v or less on a healthy electrical system).
The gauges stop working when the lights are turned on.
This is most common with incandescently lit gauges when the ground for the light has been shared with the gauge, and the common chosen ground really is not any good. When the lights are off, the gauges will find a ground path through the lighting circuit, through the filaments of the bulbs. Then, when power is applied to the lights, that previous ground source turns into power (in other words the gauges lose ground completely). Usually, the lights only light up dim, if at all when this happens.