Sidelight short circuit woes...

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Puchacz

Puchacz

Active Member
Posts
106
Location
North Scotland
Having a b*tch of a time here.

Defdender 110 200 Tdi.

The right hand sidelights keep blowing fuses.

I suspect it’s a short somewhere - if you change the fuse it’ll generally be alright for a while then go when you drive somewhere and it gets bumped a bit.

Looked at all the connections in the vicinity of the lights, front and rear. Nothing obvious. All new light fittings and bulbs. Looked at the loom where it enters/exits the chassis and there are no obvious rubbing points. Checked the number plate light and trailer light hookup too.

Got the multimeter out last night - now I’m more confused than ever. With the fuse out ALL the sidelights are showing a short circuit o_O:mad: But the left side never seems to blow any fuses.

Anyone got any suggestions short of a new loom?

Cheers.
 
Puchacz said:
Having a b*tch of a time here.

Defdender 110 200 Tdi.

The right hand sidelights keep blowing fuses.

I suspect it’s a short somewhere - if you change the fuse it’ll generally be alright for a while then go when you drive somewhere and it gets bumped a bit.

Looked at all the connections in the vicinity of the lights, front and rear. Nothing obvious. All new light fittings and bulbs. Looked at the loom where it enters/exits the chassis and there are no obvious rubbing points. Checked the number plate light and trailer light hookup too.

Got the multimeter out last night - now I’m more confused than ever. With the fuse out ALL the sidelights are showing a short circuit o_O:mad: But the left side never seems to blow any fuses.

Anyone got any suggestions short of a new loom?

Cheers.
Click to expand...

What fuse gets popped ?

It may be a chaffed wire feeding back through the sidelights .... gets bumped, shorts, bang ...
 
Remove fuse, insert two bits of wire one for each side of the fuse holder and then join a bulb to the two wires, turn sidelights on and as the wire goes/shorts to earth instead of blowing the fuse the bulb lights up and you keep wiggling/poking etc until bulb goes out and and hey presto you have found it.

Possibly a wire but I would be checking the bulb holders and of course the bulbs themselves first.
 
Puchacz said:
Having a b*tch of a time here.

Defdender 110 200 Tdi.

The right hand sidelights keep blowing fuses.

I suspect it’s a short somewhere - if you change the fuse it’ll generally be alright for a while then go when you drive somewhere and it gets bumped a bit.

Looked at all the connections in the vicinity of the lights, front and rear. Nothing obvious. All new light fittings and bulbs. Looked at the loom where it enters/exits the chassis and there are no obvious rubbing points. Checked the number plate light and trailer light hookup too.

Got the multimeter out last night - now I’m more confused than ever. With the fuse out ALL the sidelights are showing a short circuit o_O:mad: But the left side never seems to blow any fuses.

Anyone got any suggestions short of a new loom?

Cheers.
Click to expand...

What value are getting that is showing a “short”? Just because the meter is reading a few ohms, say 20-50, doesn’t mean it’s a dead short and could be a sign of something else.
 
lynall said:
Remove fuse, insert two bits of wire one for each side of the fuse holder and then join a bulb to the two wires, turn sidelights on and as the wire goes/shorts to earth instead of blowing the fuse the bulb lights up and you keep wiggling/poking etc until bulb goes out and and hey presto you have found it.

Possibly a wire but I would be checking the bulb holders and of course the bulbs themselves first.
Click to expand...

Yup, usual culprits first ... then the switch ...
 
Lynall, quite probably I’m being an idiot but looking at that technique I’m not quite sure what you’re suggesting. Surely that’s just effectively using the bulb as a fuse?

It’s going to go on when you turn the light circuit on and then possibly blow/glow very bright/melt insulation on the wires when the short kicks in?

Feel free to educate me!
 
Puchacz said:
Yes Mick. Battery was disconnected, one probe on the positive stud and one on a bare metal bit of bodywork.
Click to expand...

Can you do the same again with the bulbs removed? This time, insulate the contacts on the bulb holders, so no shorts can occur. If you are still using the old style Lucas connectors, remove the bulb holder from these connections.

I quite like the simplicity of the Lucas connectors, but most on here seem to slate them.
 
Puchacz said:
Lynall, quite probably I’m being an idiot but looking at that technique I’m not quite sure what you’re suggesting. Surely that’s just effectively using the bulb as a fuse?

It’s going to go on when you turn the light circuit on and then possibly blow/glow very bright/melt insulation on the wires when the short kicks in?

Feel free to educate me!
Click to expand...


I use a headlamp bulb and it will light up as the short takes place other wise yes its acting as a bridge/fuse until the short occurs.
Im not elec genius but know from first hand experience that it works, obviously watch where you place the bulb as A it gets hot and B it will blind you whe driving at night time!

It may work with a say 21watt bulb but I have not tried that and as you say may light up all the time the power is on short or not?
 
Puchacz said:
Lynall, quite probably I’m being an idiot but looking at that technique I’m not quite sure what you’re suggesting. Surely that’s just effectively using the bulb as a fuse?

It’s going to go on when you turn the light circuit on and then possibly blow/glow very bright/melt insulation on the wires when the short kicks in?

Feel free to educate me!
Click to expand...
What Lynall is suggesting means that you now have two bulbs in series, and while nothing is shorting it means that your sidelights won't glow as brightly, and the bulb at the fuseholder will light a little. Once you make the short happen, the sidelight will go out because no power is getting to it, and the bulb at the fuseholder is now acting as a bulb normally does in a car - sitting between earth and 12V, so it lights properly indicating that you've found the short.
 
If the chafe isn't obvious near the bodywork my guess is that you'll need to look at the loom near the switch where it's all horribly crushed to hide it behind the cowl.
 
Last edited:
Thanks for the explanation lynall and boguing. Makes more sense to me now!

Rooting around at the back it looked like the loom was rubbing up against the fuel tank next to where it enters the chassis rail, had a good look at that this evening and it all seems in prefect nick with no chafing unfortunately!

The right sidelight power wire is still showing a short so going to continue rooting around tomorrow. Hate when you start pulling at a thread like this o_O
 
If you take the fuse and bulbs out the RH lighting circuit should measure completely open circuit (max resistance) when measured at the fuse holder. If it does not, you can start by disconnecting the circuit at the rear lights (behind the little panel on the drivers side). if that doesn't change things disconnect the front at the wing, etc etc. Don't forget to look behind the dash - there are lots of sharp metal edges in there.
 
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