Dave’s wrestling with headlight globe failure, expounding the merits of club permit schemes, analysing fuel consumption characteristics at idle, and there’s yet another Commer Knocker yarn.

Idon’t know about you, but there’s no way in the wide world I’d replace one side of a set of brake pads. Neither would I (or, presumably, you) replace one windscreen wiper. Or half the spark plugs. But there is one pair of components in most cars that we’re entirely happy about replacing one at a time. Globes.

Headlight globes, tail-light globes, doesn’t matter. One blows, we’re usually quite okay with changing it for a new one. But something happened to me the other day that made me question this.

Now, I’ll preface this by saying that I haven’t had too many headlight globe failures over the years. Which is why what happened is all the more bizarre. One of my cars (a Toyota LandCruiser) blew both its H4 low-beam bulbs (and only the low-beam part) within about 12 hours of each other. Now, you might think that’s one hell of a coincidence. But I’m not so sure it was (a coincidence). See, this is the second time this has happened to me in the last 15 years or so. Back then, an AU Falcon XR6 Ute I had blew one low-beam globe on the way to the airport, and the other one on the way home next day. Spooky? Maybe, maybe not.

I asked Torrens if he’d had the same experience, and he has! And he puts it all down to the fact that globes when globes are fitted as a pair, they’ve usually come from the same factory, down the same assembly line, on the same day, with the same assembly workers using the same raw materials. Then you or I buy the globes, usually as a pair, in the same packet. Fitted to a car, both globes then see exactly the same amount of time in use and are subjected to the same extremes of temperature and vibration. Which is why, Torrens and I concluded, that they often seem to blow as a pair within a few hours of each other.

I guess the point here is that if one’s blown, the other isn’t going to be far from doing the same. At which point, you’re better off buying them as a pair and replacing them in pairs, rather than replacing one and waiting for its mate to go pop just as you’re packing the tools away. I’d bung the unblown one in the glovebox wrapped in a rag as an emergency spare, but I reckon from now on, I’ll be doing globes like I do wiper blades… in pairs.

As an aside, testing the low-beam circuits on the old Cruiser (to make sure it was both bulbs that had blown, not a fried wire or something silly) I couldn’t figure out why the test-lead didn’t want to light up when I thought it should have. Turns out, Toyota switches its headlight circuits on an 80-Series (and many other models

I’m told) through the negative side of things, not the positive as I’d assumed. I don’t imagine it makes any difference to how the lights work, but can anybody out there enlighten me as to why Toyota might have done this? I’m sure there’s a perfectly logical explanation, but I’m damned if I can think of it just at the moment.