Truck starts loosing power if park lights are on. Truck will die if head light are turned on. What might be the problem? Had Alternator and Voltage regulator checked and they are good.
Were they checked "under load" or just checked? Sometimes an alternator can function under normal conditions but not when you start adding extra power usage. To "load check" it, hook up your meter and start the engine. Take a reading, which should be in the 13.5-14.2 volt range. Have someone start turning on power users; radio, lights, heater, etc. You should notice a quick flicker on your meter and the charging rater should return to the 13.5 or better. With everything turned on it will drop some from the initial reading but should remain in the 13 volt range. If it doesn't remain in the range then it has a burnt diode in the circuit and will have to be rebuilt. Hope this helps.
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Thanks for your last reply. We did not check it under load, so I had them check it under load and alternator was bad. Replaced the alternator with new, and truck does not loose power when parking light are on, but will die when head light are turned on, or when I turned the fan for heating\cooling on. It seems any draw of major power shut the truck down. I have been looking to see if any wires is grounding out but unable to find anything.
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