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FORD BRONCO -> IGNITION; plugs/wires, distributors, MSD, firing orders; switch & ignition actuator rod, TSBs... -> Ballast Resistor
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Source, Ford, .7-1.5 Ohms, 200 watts, for the Mallory® Unilite® and Mallory® Magnetic Breakerless (MBI) Distributors
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Sources, Ford, 78-'82 M-block truck engine, w/Ford part number and wire lengths
Source: by Bubba (Dave R) via miesk5 at FSB
Sources, Ford, 78-'82 M-block truck engine, w/Ford part number and wire lengths
Source: by Bubba (Dave R) at via
Symbols in Wiring Diagrams
Source: by Steve83 (Steve, That dirty old truck) at
Testing; "...Traditional points ignition systems use an inline voltage-dropping ballast resistor between the ignition switch and coil positive terminal to avoid burning out. On the other hand, many modern electronic ignition systems require a full 12 volts at all times to develop max voltage potential. In lieu of an easily recognizable separate ballast resister, most stock wiring harnesses use a calibrated resistance wire hidden underneath the wrapped harness assembly. With the typical butchered harnesses found on many aging points cars, how do you for sure if a resistor wire is present? You should try connecting an ohmmeter between the battery positive(+) & coil positiive(+) terminals (after first disconnecting the negative battery cable). A reading of 1.30 to 1.45 ohms means a resistance wire or inline ballast resistor is present in the harness..."
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Thick Film Ignition 22K Ohm Resistor Overview & pic"...This 22,000 ohm resistor is connected to the negative terminal of the coil primary in the Ignition Diagnostic Monitor (IDM) circuit connected to the PCM. Every time the PCM sends a SPOUT signal to the module to fire the coil, the PCM expects to see a voltage signal on the IDM line telling it the coil actually fired. If there’s no confirmation signal on the IDM circuit after the SPOUT signal is sent, the computer assumes that a misfire has occurred, and stores a trouble code. Don’t confuse the IDM with the operation of the OBD II Misfire Monitor..."
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