![]() ![]() As resistance decreases with heat, current flow across the instrument increases to move the needle higher.Įach instrument has two posts-one with five volts of power (positive) and one to sender (negative ground) When you start a cold engine, current flow across the temperature gauge is nil and the needle remains on "L." As the coolant warms, resistance across the sender decreases, allowing more current flow to ground from the gauge. Like other sending units, it operates on variable resistance. ![]() The coolant temperature sender in your engine's water jacket has an electrical conducting spring, temperature sensing element, and heat conducting disc inside. Trouble-free, solid-state voltage regulators are also availableĮach sending unit varies resistance to current flow to negative ground. Word to the wise is to use a genuine Motorcraft voltage regulator because some aftermarket replacements have proven troublesome. When instruments stop working, most of the time it's a faulty voltage regulator. Twelve volts enter and approximately five volts exit to provide regulated instrument voltage. This is a typical voltage regulator, which can be found on the back of Mustang instrument panels. These bimetallic springs are very sensitive so they respond quickly to temperature change. When you turn the ignition off, current flow stops altogether, causing instrument heating elements to cool and returning needles to rest. When current flow is low, the heating element cools, causing the bimetallic spring to contract, moving the needle back to the left. When current flow across the heating element increases along with corresponding temperature, the bimetallic spring expands, moving the needle higher on the gauge face. And each has a heating element (resistor) designed to act on the bimetallic spring and needle. Each gauge has a bimetallic band tied to the needle. Lower volume or dim lights and you are increasing resistance to current flow (high ohmage).Įach instrument (except ammeter) works similar to the voltage regulator - heat and its effect on dissimilar metals cause an immediate expansion along with needle movement. Raise the volume or brighten the light and you are reducing resistance to current flow (low ohmage). Each gauge's sending unit works like the volume control on your stereo or dimmer switch. And when current flow to ground is low, instruments read low. When current flow is high to ground, instruments read high. They vary current flow to negative ground to provide readings on the instruments. All sending units, which are variable resistors (also called rheostats or potentiometers), do the same basic thing. ![]() Temperature, oil pressure, and fuel quantity gauges are all identical instruments behind the face, although they have different sending units and faces. These five-volts of regulated current from the voltage limiter flow through your instruments, which have their own unique function inside. Mustang temperature, oil pressure, and fuel gauges are all the same inside. A radio noise suppression choke wired in series with the constant voltage supply lead reduces the noise. Because vintage Mustangs were born in the age of AM radio, this pulsing causes radio interference. It is a micro-fine, constant pulsing process of contact points that keeps voltage close to five volts. "Bimetallic" means two metals - two dissimilar metals that expand and contract at different rates to open and close contact points inside the voltage regulator. Voltage regulators fail when contact points burn and pit or the resistor burns out and doesn't get warm anymore. It is this balance of heating element and bimetallic arm with contact points that regulates current flow to your instruments in half-second pulses of electricity. Inside, the voltage regulator has a bimetallic arm and heating element (resistor). Temperature, oil pressure, and fuel quantity gauges operate on five-volts of regulated current thanks to a small voltage regulator on the back of the instrument panel, also known as a voltage limiter or voltage reducer. Ohms are an important element to understand when you're checking resistance values in a circuit. It also controls how fast something operates or how brightly. This resistance, also called ohms, creates heat. Mustang instrument function tends to be about resistance to the flow of electricity across a circuit to achieve a given function. And that's what we're going to talk about here. Aside from the speedometer, which is mechanical and cable-driven, Mustang instruments are all electrical in function. Thankfully, Mustang instruments are easy to diagnose and fix once you learn how they work. If you've driven classic Mustangs for any time at all, you know that their instrument panels go haywire from time to time. Get Your Mustang's Gauges Back On Track By Understanding How They Workįrom the May, 2010 issue of Mustang Monthly ![]()
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