Question about 1985 Ford F150
The ignition systems on vehicles with points in the distributor to switch the coil had a Ballast Resistor either near the coil (in a ceramic block) or incorporated into the wiring harness. The value is about 0.5 ohm cold, and will drop the battery voltage down from 12 V to around 7-8 V and is used to limit the current through the points to prevent premature burn out. The coil in this setup is stamped on the bottom “Use with Resistor”. With this type of system, when the key was turned to start, the Ballast Resistor was bypassed to give maximum voltage to the coil and hence good spark to the plugs when the battery voltage was being pulled down by the high current draw of the starter
Once the key was returned to the run position the resistor was back in circuit. If the Ballast Resistor has a high resistance, the engine will start but not continue to run for long because there is little or no power to the coil. Your test of jumpering the battery direct to the coil tends to indicate this. When the Ballast Resistor goes open circuit the engine will start but not continue to run at all. First make sure the low voltage connections to the coil are clean and tight.
If the Ballast Resistor is easily visible adjacent to the coil, then a replacement from an auto parts retailer should solve the problem. If the Ballast Resistor is incorporated into the wiring harness, you may need the help of an auto electrician to fix the problem
Posted on Sep 13, 2010
The altinator sounds to be unservicable...Hope this helps.
Posted on Sep 13, 2010
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Posted on Jan 02, 2017
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