What fuse powers the instrument cluster gauges on the 1990 Bronco?

With the ignition switch in start or run, the gasoline and diesel engine gauges and several indicators are powered by fuse 18 through the 640 (R/Y) wires.

What resistance should the fuel sender read when the tank is full or empty?

The fuel sender has a resistance of 145 ohms when the fuel tank is full and 22.5 ohms when the tank is empty.

What are the coolant temperature sender resistance values?

The coolant temperature sender provides 74 ohms of resistance when the engine coolant is cold and 9.7 ohms when the engine is hot. The diesel engine's gauge uses an overheat switch that closes at approximately 247°F.

How does the oil pressure switch operate?

The Oil Pressure Switch closes under normal operating conditions of the engine and is open with the engine off and no oil pressure. It controls the pointer position of the magnetic Oil Pressure Gauge.

What triggers the Engine Warning Indicator?

The Engine Warning Indicator Module, part of the cluster assembly, lights the indicator when it senses a high coolant temperature condition or a low oil pressure condition (on gas with tachometer and diesel models).

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1990 Ford Bronco Instrument Cluster Circuit Operation & Sender Specs (60-7)

Ford instrument cluster how the circuit works, page 60-7, gauge and sender operation

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Shop manual page 60-7 explaining how the magnetic fuel, coolant temp, oil pressure gauges, tachometer and voltmeter operate; fuel sender 145 ohms full / 22.5 ohms empty.

AI caption June 2012 · Photo 1416 of 1799

This is page 60-7 of a Ford electrical/vacuum troubleshooting manual (EVTM) covering the Instrument Cluster circuit, uploaded as applying to a 1990 Ford Bronco. The page explains "How the Circuit Works": with the ignition switch in start or run, the gasoline and diesel engine gauges and indicators are powered by fuse 18 through the 640 (R/Y) wires. It describes the magnetic gauge design (coil, magnet, pointer) and gives key sender resistance specifications useful for diagnosis: the fuel sender reads 145 ohms with a full tank and 22.5 ohms empty; the coolant temperature sender reads 74 ohms cold and 9.7 ohms hot; the diesel coolant overheat switch closes at approximately 247°F. It explains the Oil Pressure Switch operation (closed under normal engine operation, open with engine off/no oil pressure), the Engine Warning Indicator module (lights on high coolant temperature or low oil pressure), the Tachometer (driven by ignition coil pulses on gasoline engines, by the Engine RPM Sensor on diesels), and the Voltmeter (indicates battery state of charge with the ignition in START or RUN). A boxed note directs readers to section 33-01 of the shop manual for further diagnostic information. This page is useful for testing fuel/temperature senders and understanding cluster gauge operation.

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Frequently asked questions

What fuse powers the instrument cluster gauges on the 1990 Bronco?: With the ignition switch in start or run, the gasoline and diesel engine gauges and several indicators are powered by fuse 18 through the 640 (R/Y) wires.
What resistance should the fuel sender read when the tank is full or empty?: The fuel sender has a resistance of 145 ohms when the fuel tank is full and 22.5 ohms when the tank is empty.
What are the coolant temperature sender resistance values?: The coolant temperature sender provides 74 ohms of resistance when the engine coolant is cold and 9.7 ohms when the engine is hot. The diesel engine's gauge uses an overheat switch that closes at approximately 247°F.
How does the oil pressure switch operate?: The Oil Pressure Switch closes under normal operating conditions of the engine and is open with the engine off and no oil pressure. It controls the pointer position of the magnetic Oil Pressure Gauge.
What triggers the Engine Warning Indicator?: The Engine Warning Indicator Module, part of the cluster assembly, lights the indicator when it senses a high coolant temperature condition or a low oil pressure condition (on gas with tachometer and diesel models).