MOT due and she's developed an electrical fault!

The MOT is due on Monday and of course the old girl has decided to keep me on my toes by developing an electrical fault, which would be a failure. Here's the description and what I have done so far:

The passenger side side lights work with the switch on sidelights and on main beam, so long as the engine is not on. Switch on the engine and the fuse for the passenger side sidelights blows. Possible other faults: the headlights might just turn off occasionally, this has only ever happened when lighting levels are high enough that you wouldn't really notice. Secondly the reverse light doesn't work, but I haven't investigated this yet and mght be unconnected.

I have inspected the wiring at the rear and front side lights, as well as the light fitting. I have also inspected the stick switch. All seems well. I have cut off the trailer socket, as I know that is old and water had penetrated it (I've got a new one to replace it).

All and any help/advice really appreciated.

James

first thing id do is check the voltage coming out of alternator ,engine stopped ,running and when increasing revs

Hi James,

Thanks for your help. I got:

Stopped: 12.7v
Idle and at revs: 14.2v

Thought I would test the battery whilst had my meter out, this is what I found:

Stopped: 12.6 to 12.8v
Key to possition 2: 11.7 to 11.8v once the click (coil relay?) it recovers to 12.2 to 12.3v
Start: 9.9v
Engine Idling: 14.1v

Any thoughts, beyond that the battery (a Bosch) hasn't lasted too well (it's only 2 1/2 years old).

James

I doubt I can help but people are going to need to know.
Model
Year
Engine
When exactly does the fuse blow?
When you turn the key to aux(dash warning lights on)?
When you start cranking?
When the engine is running?

Hi,

Yes, good advice.

Defender 300tdi 110 1997

Blows a fraction after the engine has started, up to this point it seems fine.

Many thanks,

James

James2 said:

Hi,

Yes, good advice.

Defender 300tdi 110 1997

Blows a fraction after the engine has started, up to this point it seems fine.

Many thanks,

James

Click to expand...

Possibly a chafed cable (a common issue in the Left wing), the vibration and rocking of the engine as you start it may be causing a temporary short which blows the fuse. Try wiggling the looms at the top of the wing around the windscreen washer bottle / heater air intake ducts to see if that changes the fault. May last long enough to get the MOT done and fix it in slower time

James2 said:

Hi James,

Thanks for your help. I got:

Stopped: 12.7v
Idle and at revs: 14.2v

Thought I would test the battery whilst had my meter out, this is what I found:

Stopped: 12.6 to 12.8v
Key to possition 2: 11.7 to 11.8v once the click (coil relay?) it recovers to 12.2 to 12.3v
Start: 9.9v
Engine Idling: 14.1v

Any thoughts, beyond that the battery (a Bosch) hasn't lasted too well (it's only 2 1/2 years old).

James

Click to expand...

it was if voltage rose when engine was reved i was getting at