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T3DDY14

Member Since: 23 Jul 2020
Location: Kent
Posts: 32

1998 Defender 110 300 Tdi HT Alaska White

Ground fault? Voltage fluctuates while idling

Hi, got an odd issue with my 300tdi when ever I'm idling IE at a stop light/ junction or coasting my lights and voltage seem to drop, I initially thought it was the belt but that's still only a few k old and had a new alternator installed last year. I've checked the grounds on the transfer box and rear chassis as I thought it could be a grounding issue as my trailer light indicates when indicating left or right. Any help would be Greatly appreciated.

Some information about the car in terms of electronics, there's a split charge system for two batteries but only one is connected at the moment, it has a android head unit and led headlights,brake lights and indicators

18th Dec 2024 12:20am

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20441

How much does it fluctuate by?

+/- 0.2v each way is pretty normal, at idle it should stay quite stable really, but is normally a little lower than higher revs, but normally not by much.

If the Alt is getting on, it might be the regulator. Do you have any variable electrical loads?

I wouldn’t like to see much below 14.1v.

Mine seems to sit around 14.4 to 14.6v, 14.5v is typical and quite static with no load or little load I should say.
With a good 60A load plus a few hundred mV difference can be normal.
I’d imagine if you are getting more than 0.5v drop or fluctuation with no real load on it, it might be time to try a new Alternator. $W33T $0U7H3RN $UG4R
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18th Dec 2024 6:14pm

T3DDY14

Member Since: 23 Jul 2020
Location: Kent
Posts: 32

normally its at 15.8v roughly, but when it dips it goes down to around 13.6/8 and it gets worse when wipers or heater are on, and the trailer light also seems to turn on when it dips down. whats confusing is this is a year old alternator so surely it hasnt failed already

19th Dec 2024 3:05am

Will@LRW

Member Since: 04 May 2019
Location: UK
Posts: 183

1997 Defender 110 300 Tdi CSW Alpine White

One thing to check is that the alternator has the superseded smaller pulley to increase alternator RPM https://www.lrworkshop.com/parts/STC3202

The aftermarket alternator I bought had the larger pulley even though I bought the later part number LR Workshop
Find a Defender's history and spec: https://defender.lrworkshop.com

19th Dec 2024 10:04am

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