I’ve been in this business since the early seventies, and the guys who are my age and older know that there was a time when the most complicated electrical issue we might encounter on a vehicle would be turn signals or power windows. Even back then things happened that didn’t seem to make sense. I encountered a ’78 Dodge pickup with an inoperative left-hand turn signal – after checking bulbs, wiring, grounds, etc. I discovered that simply replacing the flasher brought both sides back online. Never quite understood that one.
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Then there was the ’66 Cadillac convertible with a driver side power window issue that would come and go, and as I dug into that one I found a pushed back pin in a connector at the left kick panel – and from the condition of the harness and the connector it appeared that it had been that way since the car was brand new.
Once my brother’s 78 Cadillac developed road-speed radio static that he only noticed after the tires were rotated; back in those days you weren’t supposed to cross-rotate radial tires, and while I was digging in the dash for issues with the antenna and whatnot, he noticed from looking at his spoke rims that the tires had indeed been cross-rotated – and when we put them back like they were supposed to be, the while-driving radio static evaporated.
Then there was the 80 model Lincoln that would buck and skip exactly five minutes after a morning cold start but would never do it again while the car was warm – and that turned out to be a pushed-back wire in the crank sensor connector pigtail. I can’t explain the five-minute deal, but when I seated that connector the problem was gone.
I knew of one six-volt vehicle from the ‘50s that wouldn’t spin and wouldn’t start with the key but would instantly fire up if you put it in gear, pushed it, and popped the clutch. That one turned out to be a bad engine-to-frame ground.
This little old S10 had a lot of other issues that had been ignored until it developed a headlight issue, and if somebody’s planning to drive at night or in the rain, the headlights are a must-have. Initially, I was thinking this would be a slam-dunk. How hard could it be to figure out a headlight problem on a 15-year-old domestic? Well, we hadn’t tackled one of these S10 headlight issues before, and this one was a wakeup call.
|Drawing a headlight job on a truck this old would seem to be a simple exercise.|
The initial concern was that the headlights tended to only illuminate on flash-to-pass. Occasionally they would work normally, but usually they wouldn’t. Heck, the Daytime Running Lights wouldn’t even work. The owner of the truck couldn’t care less about the DRL, which isn’t required in these parts – he just wanted to turn on the light switch and see where he was going at night.
To begin with, I like to see if power and ground are available at the bulbs with the circuit energized, and as we traveled that path, we got side-tracked when we found that we only had ground at the right front headlamp – with the bulbs unplugged, there was no ground at the left front lamp, but with the right front bulb connected, we had a ground. This tended to confuse the student I had doing the work, and so we waded into the wiring schematic – which became even more confusing. Folks who are familiar with this platform are already smiling, I expect.
One of the maddening things about so many of today’s schematics is how they move from page to page with those funky arrows. Granted, the shop manual folks sometimes give us link boxes on those arrows so we can jump right to the page where the circuit continues, and that’s a good thing. Gone are the days when the entire vehicle schematic could be found on just one page (of course, that was in the 1960s). This schematic was light years away from that one-page utopia, and besides all that, it broke some key rules.
I teach my people that, in most cases, on a schematic, power comes in from the top and ground comes up from the bottom of the diagram. And that’s usually the case, although I’ve seen it violated a few times on isolated schematics for one reason or another. Well, this S10 schematic shatters that rule and inserts some other curve balls in the process.