Land Rover 90 - blowing fuses...

Hi,

Anyone here any good with electrics etc please take a look at: www.landyzone.co.uk/land-rover/land-rover-90-blowing-fuses.353549/

I've got a couple of electrical issues; fuses blowing, no tail lights and no intermittent wipers.

I did some testing with the multimeter.

The sidelight itself measured the same resistance as the working one.

I then did green wire to ground and got 3 ohms, black wire to ground 0.

On the side working both got 0 ohms which says to mean the issue is with the green (live?) wire on the other side.

I traced the wire back and it goes into the loom and then off out of sight. How can I locate the short without pulling a load of wiring and parts out?

Have a good read of the manual wiring diagram, the lighting and wiiper ccts on Defenders is terribly easy; but you need to confirm what year/engine you have. You need to say which side rear tail lights failing, or both + are both rear tail light fuses blowing [RO & RB] and/or the wiper fuse [G]. Do the rear tail lights work with no blown fuses if you turn off the wiper switch and remove the wiper fuse? If so, this will help you track down a potential short between these to functions. When tracing electrical gremlins start by separating the ccts and if possible measuring for good 12v through the cct. If no 12v, isolate the wires from, in this instance the bulbs, and short to chassis, this will close the cct and you should see 12v. You could also remove rear tail light fuses to isolate this fault/failure and then separately check the wiper ccts. If this is still failing you have a wiring short between the two [one's pulling the other cct to ground/or 12v with a higher load from the wiper motor] which means you simply inspect the wiring loom shorting wires, usually caused by a longterm fault leading to overheating and breakdown of the wiring insulation. And it's worth isolating the steering columns connections in case the fault is within the columns switch [28]. If wiring looms are in poor condition replace them as sure as eggs no soon as you've found one fault another will appear. Good luck with this...

v8250 said:

Have a good read of the manual wiring diagram, the lighting and wiiper ccts on Defenders is terribly easy; but you need to confirm what year/engine you have. You need to say which side rear tail lights failing, or both + are both rear tail light fuses blowing [RO & RB] and/or the wiper fuse [G]. Do the rear tail lights work with no blown fuses if you turn off the wiper switch and remove the wiper fuse? If so, this will help you track down a potential short between these to functions. When tracing electrical gremlins start by separating the ccts and if possible measuring for good 12v through the cct. If no 12v, isolate the wires from, in this instance the bulbs, and short to chassis, this will close the cct and you should see 12v. You could also remove rear tail light fuses to isolate this fault/failure and then separately check the wiper ccts. If this is still failing you have a wiring short between the two [one's pulling the other cct to ground/or 12v with a higher load from the wiper motor] which means you simply inspect the wiring loom shorting wires, usually caused by a longterm fault leading to overheating and breakdown of the wiring insulation. And it's worth isolating the steering columns connections in case the fault is within the columns switch [28]. If wiring looms are in poor condition replace them as sure as eggs no soon as you've found one fault another will appear. Good luck with this...

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Sorry gonna sound really thick; ccts = circuits?

Both rear tail lights don't work. There is a fuse board diagram but I can't remember what circuit they are on, I'm sure they share something else but I'll have to go check tomorrow.

DecayingRat said:

Sorry gonna sound really thick; ccts = circuits?Both rear tail lights don't work. There is a fuse board diagram but I can't remember what circuit they are on, I'm sure they share something else but I'll have to go check tomorrow.

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yes, cct/ccts = circuits

It's good news that both rear lights work :. another cct is over loading the lower amp tail light fuses, so remove the light fuses and follow back your green [G] wiper wire until you find the short+ it's worth pulling the [G] wires from the wiper fuse, column switch and the wiper motor...that way you'll be able to trace any potential [no pun intended...] short with the two [G] wires. If there is no short between [G] and [R] the fault is elsewhere and you can use the fuses/fuse holder as a cct isolation function where if no fuse and there's still a short between two non-connected ccts...woohoo, you've found the fault!

The other cct is [R] which bridges the rear light fuses with one [R] coming from the light switch [57] and the other [R] going to the panel light switch [26].

Easy trick is to get a headlight bulb, add two wires and using whatever terminals fit your fuse panel, so the bulb is b=now acting as the fuse if that makes sense? then turn the lights on and the bulb will light up nice and bright, this shows its got a dead short and all you have to do is go around unplugging stuff and when the bulb goes out your are on the right track.
Use this truck quite a bit at work, saves loads of time.

Headlight Bulb is a great idea, but if you want to pass full power then I use a 16Amp domestic circuit breaker in place of the fuse, If there is a short the breaker trips and can easily be reset.

Steve.

12 glass or 20 blade type fuse box any picts of wiring you are checking ,you can get Amazon product if you have blade type fuse box ,assuming the circuit in question is 10 amp a 16 amp domestic ac 240 volt circuit break is not a idea i would suggest as they are rated differently may trip above 16 amps in approx 4 seconds on 240 volt circuit ,hate to think what current to trip it at 12 volts dc and what temperature the cable climbed to before it did trip,

Mystery, I have used this system with great success for many years, We are looking for short circuits here not slight overload,
Before the supply wire can heat up the circuit breaker trips in milli seconds.
Try it if you dont believe me.

Steve.

Steve i'm not trying to devalue your idea it's some think that i personal would not do maybe it my lifetime of working within the various electrical industry's ,but its too easy to keep resetting the breaker thinking the fault will magically disappear
whilst the cable is subject bursts of high current possibly above 16 amps until the breaker trips that causes the problems especially if the cable is rated lower than this figure ,getting back to the problem in hand the description of the problem is quite vague could do with more info than a green wire going behind the dash and where were the reading mentioned taken at the lamp unit at the connectors ,is the harness original or part 300tdi engine harness modified to the original harness more info please

mystery said:

hate to think what current to trip it at 12 volts dc and what temperature the cable climbed to

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Me too. Have seen auto electrical fires a number of times with long term arcing where insulation has broken down due to current overload. The shorting often occurs where looms have been messed about with/not installed correctly and the loom is rubbing against a sharp piece of metal; self tapping screws and metal/stainless cable ties are classic culprits.

Steve, I really like your use of a correctly spec'd trip. Only risk with this is that it could trip leading one to think one's found the fault, when there may be another in the loom that due to another continues to overheat slowly.

All too often car wiring looms have been messed around with by owners who simply do not understand auto electrics and the importance of correctly spec'd inline fuses and correct gauge wiring. Then we have the "splicing together brigade" using domestic terminal blocks and electrical tape. It's so easy to use the right electrical components and do the job right first time round. And proper water proof electrical connectors are such low cost. The other interesting failure is simply, age...where the wiring insulation becomes brittle, breaks down and the shorting begins. I guess we're all a guilty of just accepting our wiring is in tiptop form and never give the wiring

DecayingRat, how's the fault finding going? Keep us up to date with what you eventually find. I'm sure we can help you track down the fault and complete a proper repair...