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Strange headlight issue SOLVED

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12 Dec 2025 09:28 - 12 Dec 2025 09:29 #263049 by FrankFisher99
Fixed! That's crazy, it was just the LH fuse had blown. The circuit must use that permanent live/switched earth approach to do just this  let each bulb fall back to a parasitic draw if the fuse or supply fails? Crazy. But, that's all it was. Let's see if the fuse blows again.
Last edit: 12 Dec 2025 09:29 by FrankFisher99.

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12 Dec 2025 10:33 #263051 by fordem
There is no parasitic draw involved here.

The lamps are fused separately to prevent a blown fuse from leaving you in total darkness, to achieve this would require either multiple switches (one per light) or ground switching, manufacturers choose the least expensive route which has the side effect of allowing one lamp to be back fed from the other.

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12 Dec 2025 12:29 #263052 by DrRobin
Replied by DrRobin on topic Strange headlight issue

Hi all, gen 3 Jimny, my left headlamp is very dim, right is fine, but when I take out the right hand bulb, the left goes out - as if they're wired in series! That can't be, surely, so any other thoughts before I start digging into the wiring? Nb, we also have a battery drain, possibly connected?
 
Great news the headlamp issue is fixed, but that doesn't explain the current drain, so you are probably looking at an unrelated problem.
Just for reference, my Gen 3 drew about 40mA when just sat there, that doesn't sound much but 

0.04 x 24 = 0.96Ahr per day.

Given that the battery is only 40Ahr, that's about a month before the battery is flat.

2020 blue SZ5 (one of the last to be registered in the UK)
Ex 2011 Blue Jimny SZ4
Northumberland Jimny Blog

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12 Dec 2025 12:37 #263054 by facade
Replied by facade on topic Strange headlight issue
I'd cast an eye over the wiring, the fuse for each light is 15A, and the light normally takes 5A- it can only draw 10A if you run both filaments at once (by having it on dip and holding the flasher switch back). Unlikely to just blow through old age

If it suddenly breaks, go back to the last thing that you did before it broke and start looking there :)

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12 Dec 2025 12:39 #263055 by DrRobin
Replied by DrRobin on topic Strange headlight issue

I'd cast an eye over the wiring, the fuse for each light is 15A, and the light normally takes 5A- it can only draw 10A if you run both filaments at once (by having it on dip and holding the flasher switch back). Unlikely to just blow through old age
 
If a bulb blows, it can sometimes draw a large current as it burns out and this can cause a fuse to blow, although I agree, a quick check of the wiring would be a good idea.

2020 blue SZ5 (one of the last to be registered in the UK)
Ex 2011 Blue Jimny SZ4
Northumberland Jimny Blog

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