Ford Truck Engine Hesitates when Headlights are turned on!! Why??

I just had an experience this morning with Ford trying to nail down a problem that has been hassling at least four of my customers with late 80s Ford F-150s. Occasionally, when turning on the headlights or using the flashers the engine stumbles for an instant - this has been bugging me for a year or more and I even stopped by the local Ford shop last spring to ask if the service manager knew anything about the symptom. No clue, was the answer.

I was poking through the TSBs on my vehicle and came across the following:

272. 881616 AUG 88 An Engine Stumble/Miss When Headlamps On/Off

WOW!!! The actual problem I was trying to solve was listed there in terms even I could understand!!! Next problem was to find out what the service bulletin said! A call to the local Ford dealership yielded a dead end, even with the actual TSB number in hand. I was given a "Hot Line" number to call 1-800-392-3673 where I was connected to a very polite but highly un-knowledgable young woman who didn't even know what a TSB was. After 15 minutes of working with her on the phone it was determined that she could not help me either, and I was given an address to which I could write to get the information I needed - maybe. That was her only call escallation procedure! She wouldn't even connect me to her supervisor!!

Not wanting to look for an envelope and a stamp and feeling that there must be a better way than snail mail I started calling other Ford dealerships. On the third try I hit gold!! The service manager actually read the TSB to me in its entirety - "connect a ground strap from the headlight surround sheet metal to a good engine ground, preferably directly to the battery ground strap" He even gave me a Ford part number for the recommended strap assembly!!

From what he told me I concluded that there must be a ground loop generated thorough the sheet metal surrounding the headlights and directional flashers. I used a piece of 10 gauge wire with a fast-on ring terminal on each end instead of the Ford part and installed it today. So far, after a dozen attempts to make it stumble with the high beams it hasn't done it yet!

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