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20amp aux fuse keeps popping


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Hello all,

My 1990 110 2.5TD has developed a fault with the aux fuse keeps popping. It's the top left one, and should be powering the horn, back fog light (?), this also affects the light stick when pulled back to put full beam on for a few seconds. The voltage is 12.8 when the engine is off. Any ideas on what to check or try? I'm guessing an earth wire somewhere or a short of some sort. Checked and it's marked as 20amp and have been putting in a 20amp fuse.

I've checked with new light Indicator-horn-headlamp dip switch
Disconnected all the connectors in the engine bay for the water pump
Swapped the hazard switch for another one
Removed the other switches such as lights and heated window (which was not connected to anything :D)
No cigaret lighter or USB connectors on either

All and any helpful suggestions welcomed.

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Hi,

This is my fuse cover.

The interior light only has one wire connected at the top, I will rip down the covering to see if the other is hidden.
The rear fog light works ok, the horn was disconnected as it seemed to be linked to the fuse issue. Made no difference connecting it back up.

2.5td 19J - Fuse panel.jpg

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Hi Ian,

I've not checked it, as I don't have a spare. I disconnected all three of those; the hazard, interior lights, and windscreen heater. Still has not isolated the issue. I'm guessing a damaged wiring that needs to be found and replaced.

Sean

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If you can access them, unplug everything on that fuse and reconnect them one at a time until you find the culprit that's popping the fuse. Then you'll have to turn detective with the offending circuit to find the cause of the extra current draw and so determine why the fuse is blowing.

HTH

Mo

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Hello Ian / Mo,

Tried unplugging all the fuses and seeing if there was one that did it.

Sorry I didn't say, the engine is off, and this happens instantly

I guess I’m going to have some fun stripping the wing down to get to the wiring loom :D

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9 minutes ago, Sean. said:

Sorry I didn't say, the engine is off, and this happens instantly

Do you mean:

  • as soon as you connect the battery
  • or as soon as you turn the key to start it?
  • Or even as soon as you turn on anything on that fuse that you mentioned earlier (flash, hazard, horn etc).
  • Or as soon as you put the new fuse in?
  • Other
Edited by timc1967
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That's a bugger.

I had a power drain on mine, as I connected the battery I could hear a relay clicking on, and found the previous owner had wired the spot lights through a relay that was powered even with the engine off. All removed and now no power drain. That doesn't help you though.

But it does make me wonder, have you removed any of the relays in the fuse box? Could be a problem in one of those.

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You might have to remove part of the dash , check the earths attached to the bulkhead in the engine bay and there will be some more earths attached to the bulkhead behind the instrument panel , I think as Mo said your going to have to take each thing wired into that fuse in turn and check the wires from end to fuse box . Don’t envy you on this one Sean it’s going to be a right pita . Also we’re all the wires from the fuse box go up behind the dash check at the bottom and were they come out the top in case they’ve rubbed on the dash .

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Get a small 12v bulb with some wire attached (eg an accessory warning light) and wire it across the fuse holder with  no fuse. When the bulb lights you have your short. Then you can start unpicking stuff/jiggling harnesses etc to see where the problem is. The current through the bulb is going to be limited by the bulb so no harm done.

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No not quite, just remove the fuse (or if blown you  could leave in place) but put a small bulb in parallel with the fuse, ie across the fuse holder., connect it as if it was the fuse Then if there is a short(and we think there is!) the bulb will light up. In any case  its resistance will be large versus other stuff on that circuit, so it will limit the current and show you if current is flowing. A little bulb will only pass a fraction of an amp, so no wiring will be damaged even if there is a short. When the light goes out you have found the problem.

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Hi Cackshifter,

Tried as you said. The new LEP brake lights work a treat with the pins on them!

Now I am guessing it's a case of what item has melted and caused this issue! Internal lights, horn, or fog lights?

Defender 110 2.5td 19J testing the wiring for short fuse box.jpg

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You'll have to disconnect things till you find the thing that turns off the light I'm afraid. Try the easy ones, then you are down to harnesses. The wiring diagrams give you the numbers of the connectors, and the electrical library manuals show where they are located.

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move the fusebox away from the bulkhead [2 screws hold the metal backing plate to the bulkhead, screws are 1 each side behind the mat] you should be able to se the wire colour codes of the offending fuse location, I suspect it's a plain purple or brown & direct from Battery supply.

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Unless I am completely wrong, I don't think that one will be much help. It's for a Lightweight. A lot of the colours stayed the same through the various 90/110/Defender/TD5/TDCi evolutions, but the Lightweight is out there on its own. I am just digging around for a 200 Tdi diagram. I've got a full copy of the TD5 stuff which has been invaluable for the V8 conversion I'm involved with. 

If we had a diagram, we could put together a quick test procedure to narrow your search. Of course, it's possible that a previous owner has hung another circuit on that fuse. Do you have any extra auxiliary lights or similar?

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