BMW 7 Series 3 years old. Has tw lights in the boot. One under the parcel shelf and one in the lid. No sign of water ingress. Very strange. Any bright ideas out there (excuse the pun)
- posted
4 years ago
Boot light keeps blowing fuse
Loading thread data ...
- Vote on answer
- posted
4 years ago
Check for broken insulation in the wiring, particularly where it comes into contact with a metal edge/corner.
- Vote on answer
- posted
4 years ago
Are you certain they are properly switched off when the boot is closed? Not flickering etc with movement? Some use a switch which works on the lid angle, rather than the sort operated by the doors for the interior lights. And that could be faulty.
Light fittings designed for only short term use may well allow the bulb to get too hot if left on for long periods.
- Vote on answer
- posted
4 years ago
If it's blowing a fuse there's a short somewhere. No mystery about that. You just gotta find it. And that's no fun. I'd start by removing the lamps so there's zero load, then replacing the fuse with a resistor, and monitoring the voltage on its output. Disconnecting bits where accessible will show you when the short goes away.
NT
- Vote on answer
- posted
4 years ago
It might even be one of lamps (bulbs)
- Vote on answer
- posted
4 years ago
If one of the lights in in the boot lid there must be a connection at the edge of the moving part of the boot to the main body of the car. Usually wires running in some black corrugated trunking. As the trunking, and the wires inside, are flexing every time the boot is opened or closed this would be my first place to look for damaged wiring. You may have two wires where the insulation has failed and are shorting together.
See the Youtube video related to a boot lid wiring breakage
formatting link
- Vote on answer
- posted
4 years ago
Before dismantling anything just turn on the boot lights and pull and waggle the flexi trunking to see if you can get the fuse to blow (as indicated by the lights going out)
- Vote on answer
- posted
4 years ago
3 years old? I'd be harassing the dealer. If it isn't covered by warranty it darned well ought to be!
Frayed or shorting connections are possible for sure, but shouldn't be happening on such a young car.
Tim
- Vote on answer
- posted
4 years ago
snipped-for-privacy@gmail.com wrote on 22/10/2019 :
A small 12v lamp would be even easier to use, instead of a resistor. Lit would suggest the fault is still there, unlit that there is no short.
- Vote on answer
- posted
4 years ago
+1 Just the method I used to find an intermittent short which turned out to be in the feed to a seatbelt clip illumination bulb. Very much not essential.
Chris
- Vote on answer
- posted
4 years ago
About 40 years ago my mother bought a Fiat 124 which was the first car I ever saw with a boot light. I was demonstrating this to my future father-in-law when we discovered it had no switch but was permanently on
- Vote on answer
- posted
4 years ago
Thanks to all for all the suggestions. I'll have a root around on Saturday. I did get tail ended twice last year.One was just a new bumper the other was severe enough to set off the protection system. Seat belts tightened, head restraint snapped vertical (triggered by a small explosive charge apparently). That may have some bearing though all the damage was repaired last year
- Vote on answer
- posted
4 years ago
Um, sounds like bollocks to me. So the battery was running flat every day?
Tim
- Vote on answer
- posted
4 years ago
Tim+ formulated the question :
+1- Vote on answer
- posted
4 years ago
Car batteries don't run flat every day just because there is a 5W load on them. If yours do then buy a working one.
- Vote on answer
- posted
4 years ago
5W for 24 hours would be 120 watt hours; at 12v = 10 AH - quite a drain on a small battery,
- Vote on answer
- posted
4 years ago
True, I hadn?t done the sums. You still wouldn?t want one on all the time though. Wouldn?t take many days of non-use to flatten the battery.
Tim
- Vote on answer
- posted
4 years ago
Yes disconnect lights one at a time as close to bulb as possible ran till a fuse blows, if it does not with eater only on, then you have an over current situation or maybe a very low tolerance fuse. If either fixes it and you can pin it down by swapping, the junk the doff one and get another, if it still trips with no bulbs the short is in the wiring, probably where its bent or trapped somewhere by the boot lid. Its not rocket science. Brian
- Vote on answer
- posted
4 years ago
Truth probably was just a sticky switch or one timed to go off after a set period, some switches were damped by some device to do that, Maybe they did it for a reason but it eludes me. Brian
- Vote on answer
- posted
4 years ago
What about the sort of capacity battery that would have been found on something like that in 1979 in the middle of the winter?
Say it was a 40Ah new, down to 30Ah because of it's age and now 15Ah because of the cold ... and it will only restart the engine when the battery is greater than 50% charged, then it can only take a (say) .5A parasitic load for 14 hours?
I still don't believe a boot light wouldn't have a switch of some sort though, possibly a gravity one or a micro switch up in the hinges somewhere?
Cheers, T i m