What’s the dumbest mistake you’ve made working on your own car?

Allow me to reintroduce myself, my name is HOOOOO …ly hell, what did I just do?

I have done some dumb shit in my day. But last night, I managed to make a simple mistake that could potentially cost me a few bucks. Last night, I decided to swap in a new battery on my Jag. A friend had a pair of Optima Red Tops he was supposed to review, but he was sent the wrong sizes that he needed. He offered them to me if I could do a simple write-up on them. I said yes, and they’ve been sitting in the corner of my garage for at least a month now. So I got an itch to look at an engine and touch a tool. A battery swap should take five minutes, anyway.

When pulling the old battery, I should’ve taken note that although the ground terminal had a little corrosion on it, it was minor. Very minor, in fact, but it still caught my eye. What didn’t catch my eye was the fact that my battery wires in the Jag are black for the negative and beige for the positive. So I wasn’t thinking about the wires, I just assumed the one with a little more corrosion on it was the positive terminal side. I don’t know why I thought that, I just did.

I picked up the Optima. Set it in the battery tray and tightened the tie-down. Then I put the black battery cable on the positive side. It wouldn’t go on easily, which should’ve given me pause but I just assumed the terminal ends were dumb Jaguar things. So I smacked it with a hammer a few times and got it to sit better. Yes, I’m serious. After that, I grabbed the beige battery cable and put it on the negative terminal.

It snapped a bit more than you typically hear when popping on the negative battery cable. And then a good bit of smoke poured out the wire end right where it connects to the alternator. Maybe a small bit of smoke up where that cable runs back to the firewall. I popped the negative cable off immediately and stood there wondering what the fuck just happened. Unsure of what it did, I put that terminal end back on. That’s going to be your favorite part here. And yes, it did it all again. The wires were all very hot to the touch too. So I popped it off once more. Then looked down at the battery on the ground. The older battery I just pulled from the car. I remember the orientation in which it sat in the car before I removed it, and I could easily see the plus sign and minus sign. And that’s when I knew I fucked up.

This is a colossally stupid mistake on a job that takes no skill and requires minimal time and effort. Yet, I boffed it pretty fucking good. The Optima is in correctly now. I have since turned the key to the On position, and the electronics turned on. But I’m going to start it in the morning, see what the volt meter says, and go from there. It’s quite likely that I just fried an alternator that has barely been in the car for a few months. I’ve likely cooked some wiring as well. I’m not sure if it was a fusible link that went up, or something worse. I’ll report back soon.

For now, why don’t you help ease my pain with some of your own dumb stories…

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14 responses to “What’s the dumbest mistake you’ve made working on your own car?”

  1. Neight428 Avatar

    I think I’ve shared this one before here, my finest wrenching hour. I spent an entire weekend replacing bushings on the front end of my Camaro. After fighting every complication imaginable to get it done before I had to be back at work on Monday, I slapped it all back together and noticed the alignment felt awful. I figured I must have knocked the tie rods around or something that the alignment shop would fix. I dropped it off the next day to get the alignment done and later that morning, the shop informed me that I had the upper control arms swapped to the wrong side. I admitted that was entirely possible, but wouldn’t have figured that it would have bolted up at all, the mechanic sympathetically agreed, but I think he was just being nice.

  2. Maymar Avatar

    On a similar misstep, several years ago, I came home from a weekend away to find the battery dead on my car (I’d left the light on grabbing a pair of sunglasses or something before leaving). Being sleep-deprived from getting stranded in Newark the night before, I hooked up the jumper pack the wrong way, and proceeded to kill like half the fuses or something.

    The worst though, was doing an oil change, in my driveway, at roughly 11 at night, two days before Christmas. I got distracted by obliterating the over-tightened filter trying to get it off, and forgot I had only hand-tightened the drain plug. It at least made it 15 miles to work the next day without falling out, but starting it at the end of my shift must have shaken it loose, which I figured out once the low oil light came on about a mile away. At least I was able to find it in the giant pool of oil in my parking spot at work, and there seemed to be no lasting damage (my grandma absolutely refused to wait for me to show up before serving Christmas dinner though).

  3. OA5599 Avatar

    Whenever I swap out a battery, I always look at what I believe to be the negative battery cable and trace it to the nearest ground connection for confirmation before making the final connection. I don’t remember when I started doing that, but I suppose an experience similar to Jeff’s must have gotten me started.

    I do recall another battery-related incident, though. I have a friend who was doing something under his hood while wearing a watch with a metal band. He did something where his arm was close to the battery, and the band completed the circuit between the positive terminal and something grounded. His watchband got red hot and left a permanent reminder on his wrist.

    Many years later, I was under the hood of my own car, and I realized I was wearing a watch with a metal band. It was a very nice watch that I received as a special graduation present from a great aunt. I took off the watch and set it on the radiator support. When I finished my maintenance task, I shut the hood and went on a short test drive. When I got back to the driveway, I remembered the watch, which was no longer where I left it. It had fallen out somewhere on the test drive, but I retraced my route and never found it. Now any jewelry (to the extent I wear it) always goes inside the car (or the house if I’m at home).

    1. Jeff Glucker Avatar
      Jeff Glucker

      Yeah, after all my stupid was done I looked at the negative cable and realized it traced a nice short path to the inner fender, where it served as the grounding point. And it was in fact not the positive terminal, clearly.

      The watch thing has me spooked now. Will remove watches before wrenching.

      1. OA5599 Avatar

        I’m not nearly as diligent in removing my wedding ring around machinery and electrical stuff, even though I became aware of the risk through Hooniverse.

        Gadget Review: Recon Rings Silicone Wedding Band

  4. Feds Avatar

    During the eastern seaboard blackout of 2003, I had a couple of days off work. Perfect time to fix the stuck floats on my newly acquired RX-7.

    Try to start the car, but it’s flooded. Also, gasoline is spilling out of the carb onto the engine, because of the stuck floats.

    Pull the plugs. The coils are on the fender, so I let the the wires hang down against it.

    Back in the car, foot to the floor, crank the car over to clear the flood.

    WHOOOSH! Giant fireball into the air. The spark plug holes are on the side of the engine, so the mixture in the chamber shot out toward the fender, where the spark plug wires were.

    Rental house, so no garden hose, no nothing. THANKFULLY a quick thinking neighbour was on their porch and came running over with a bucket of water to put it out. I left the singed wire harness cover in the car until I sold it as a reminder to think twice.

  5. Sjalabummer Avatar

    Oh, man, I could provide an itemized list. But the dumbest thing I remember might be wrenching not done. When I sold my ’93 Volvo 245 with the lovely B230FX engine, it was because I was tired of constant small issues. Really nothing major and I’d look at it differently now, but we had a one year old and one more kid on the way – that does not work in brain capacity’s and overall zippiness’ favour.

    Anyway, the final drop was when the servo steering started acting weird. I was so tired, I never even checked anything. Washed the car, put out the ad, and the first buyer looks under the hood to find the servo pump lose. It was just working against itself. Tightening one screw fixed it.

    Not my brightest moment, but I sold the car and had already acquired the Honda Stream – a great purchase, maybe my best. And every moment of pure, clear dumbness is remembered for future avoidance. That’s something.

  6. Slow Joe Crow Avatar
    Slow Joe Crow

    My first and most embarrassing blunder was getting the firing order wrong on my VW Scirocco, the scariest was losing the oil drain plug from my Jetta in the middle of nowhere Missouri. Fortunately we hitched a ride and got a temporary plug to get home. Since then, the worst I’ve had was shredding the serpentine belt on my truck because we didn’t know just how much force was needed to fully seat the power steering pulley.

  7. MattC Avatar

    Two instances come to mind. Both on my wife’s previous 2008 CR-V. (For the record , this was easily one of the most reliable vehicles we have ever owned)

    First was a simple stupid mistake in my part. I had finished detailing it ((Spring detail). The wiper arms were up as I cleaned the windshield and was ready to replace the blades. I did the drivers side and inadvertently hit the passenger arm. The arm sans a wiper blade hit the windshield…hard. Instant spider webbing resulted. So fresh detail and a brand new windshield ( thanks SafeLite) thanks to my mistake.

    Second, replacing a serpentine belt on the same vehicle. Getting it off was fine. Getting new one on was next to impossible due to the clearance and a broken idler pulley(my doing in trying to persuade the belt in) resulted in the car being to a shop to fix my screwup.

  8. OA5599 Avatar

    I thought of another one. The fluid for the power top system got low, the result of which is that the convertible’s hydraulics would not fully extend. The way to refill it is to use a squirt can or syringe to inject it into the reservoir, which is built into the side of the pump. The pump is located at the front of the trunk, under where the top stows, and there is a canvas boot well between the top storage and the trunk floor.

    For best access to the pump and reservoir, the top should be up (out of the way). Gravity makes the canvas sag, but it can be propped up so it doesn’t hang down when you are under it. I decided to use a broomstick for that purpose.

    I refilled the fluid, but air remained in the lines. The easiest way to purge the air is to cycle the top a few times. I hit the down button and the top lowered a little bit, then a bit more, then…CRASH. As the top lowered, I had forgotten about the broomstick. It was precisely where the folded top would be. The canvas in the top was flexible enough, but the glass back window wasn’t. Irresistible force (the hydraulics) met the immovable object.

  9. smaglik Avatar

    My dumbest mistake was tied to an oil change on my m5. I got distracted while doing it, and neglected to put the drain plug back in before filling it. I was 6 liters in when the dim light bulb went on. Luckily I had another oil change kit for the m3 I also had at the time, which used the same oil, so I was able to complete the change, but it was still about $70 lit right on fire.

  10. Salguod Avatar

    Changed the negative battery cable on my 1976 Camaro and put the bolt in the block in the wrong hole. There were 2 threaded holes next to each other, one blind and one through a flange. I used the blind hole which didn’t clamp the cable. Car sat for a week while I tried to figure out why it wouldn’t run.

    Dad’s 1980 Citation 4 speed had a flaky neutral safety switch. One day when it wouldn’t start, I grabbed a screwdriver to short the starter terminals. Unfortunately, I had left it in reverse and it started and proceeded to lurch backwards down the driveway, with my arm completely down behind the radiator. I quickly extracted my arm, chased down the car and brought it to a stop in the across the street neighbor’s front yard, having narrowly missed their mailbox.

  11. PapaVanTwee Avatar

    I once killed a car by giving it an oil change. I put the oil plug back on right, I put the oil filter lid back on correctly as well. But what I didn’t realize is that I had rounded the “nut” on the lid to the Saturn 2.2l four’s oil filter canister (not the usual Fram screw in oil filter). That created a tiny oil leak I did not see, and it thus drained the oil on my 30+ minute commute the next day. The engine would never run correctly again after that, and I wound up donating it to our local Goodwill car auction.

    1. Sjalunker Avatar

      That’s interesting. During clash-for-clunkers there were lots of videos of cars running without oil, some with sand instead of oil, in order to immobilize them for good. I was surprised at how many engines would run fair in dry conditions for quite long. Mostly Volvos though. ?