Headlights dimmed as well as dash

Whilst feeding the horses this evening I was parked with the main beam on for about half an hour but with engine running so the battery didn't go flat. I noticed the light gradually went dim, got back in to leave and the interior lights and dash were all dim too. Pressed the accelerator and the lights all went back to normal, came off the gas and dimmed again and revs dropped really low and nearly cut out. Went for a drive and now all is fine. Any ideas??

Alternator brushes worn or defective voltage regulator.

Either way, a replacement alternator might well be on the horizon
(assuming that wiring and conections are all good)

more than likely you were taking more power out of battery than alt was putting in so therefore would dim lights ??

would also advise to get output on alt checked as could be sign that you have a "lazy" altenator ?? or battery on way out ??
you dont really say what your landy is ??

My dads an auto elec by trade but not had chance to speak to him yet, will get him to take a look when he can. It's 96 disco 300tdi


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an alternator can't charge the battery when the engine is idling and you have a heavy load on the electrical system.
so the battery will go flat.
next time try something to hold down the accelerator pedel, just enough to bring the engine up to about 1000>1500rpm, and you'll be fine.
ps watch the engine doesn't overheat!!

sparky steve said:

an alternator can't charge the battery when the engine is idling and you have a heavy load on the electrical system.
so the battery will go flat.
next time try something to hold down the accelerator pedel, just enough to bring the engine up to about 1000>1500rpm, and you'll be fine.
ps watch the engine doesn't overheat!!

Click to expand...

When mine is on tickover I get 13.8 volts when revved it drops what gives with that? Sorry for hijack lol.

stubradley1 said:

When mine is on tickover I get 13.8 volts when revved it drops what gives with that? Sorry for hijack lol.

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what does it drop down to?
is there anything switched on in the car?
and is the engine hot? ie glow plugs off.
i would suspect that when the engine is rev'ed the ecu switches the glow plugs on, this should stop when the engine is at normal operating temp..

DARREN4040 said:

more than likely you were taking more power out of battery than alt was putting in so therefore would dim lights ??

Click to expand...

He would need to be running 100amps of load! The alternator is more than able to cope with full lighting, heater, heated screens, wipers and charge the battery - unless the battery is profoundly discharged or the alternator is knackered.

If it is managing on higher revs then it does sound like a faulty alternator.

You might get away with simply replacing the brushes.

sparky steve said:

an alternator can't charge the battery when the engine is idling and you have a heavy load on the electrical system.
so the battery will go flat.
next time try something to hold down the accelerator pedel, just enough to bring the engine up to about 1000>1500rpm, and you'll be fine.
ps watch the engine doesn't overheat!!

Click to expand...

He didn't have a heavy load, he had 110watts, plus any extras! If he comes back and says he had a 1000w inverter running a kettle in the back I will stand corrwected.

There is something wrong.

sparky steve said:

i would suspect that when the engine is rev'ed the ecu switches the glow plugs on, this should stop when the engine is at normal operating temp..

Click to expand...

Unless he has changed it it's a 300tdi, the glow plugs come on for 8 seconds on start up and thats it.

300tdi doesn't have an ECU and the ones that did didn't control things like that.