Battery light on - big fuse?

[Mark.]

Went a mile down the road no problem, switch it off for 10 mins, start up again and the battery light is on. Could it be the big fuse?

I believe it's down on a chassis rail somewhere? 1996 4.0

[s p a c e m a n]

Yeah, sounds plausible. There's one on the bottom of the chassis rail, drivers side near the front wheel. Another near the battery somewhere too I think.

[Chuffmeister]

Sounds like it. It would be a good place to start and not cost much if it wasn't. 100Amp on the chassis and 80Amp under the dash IIRC.

[nawarne]

Yep, likely 100A fuse on chassis rail, drivers side near engine mount.

Not all Chims had the 80A fuse to the fuse and relay board. Certainly not the early (pre '96??) cars.
Nick

[Mark.]

Cheers guys - why do these things always happen when it's bloody cold outside!?

[Bassfiend229hp]

I wonder if yours will just fall apart when you open the fuseholder like mine did...

[Mark.]

It's a distinct possibility Phil, not been touched since I had it.

Might just stick it in the garage til the weather warms up a bit and use the other one. Who needs the roof coming off anyway.

[Bassfiend229hp]

Mark. said:

It's a distinct possibility Phil, not been touched since I had it.

Mine was over at Lloyds and they started it and it did just what you described - they lobbed in a new fuse and lubed it up for me for free.

Mark. said:

Might just stick it in the garage til the weather warms up a bit and use the other one. Who needs the roof coming off anyway.

[QBee]

It's one of two things:
100 amp fuse
Alternator

Not the 80 amp in the footwell - nothing much would work if that one had gone.

I have had the fuse go twice, the alternator once.

I don't remember the battery light coming on when the fuse went.
I do remember it coming on when the alternator failed on the back straight at Cadwell Park.

The 100 amp fuse is between the battery and the alternator. If it goes the alternator cannot charge the battery.
If the alternator goes, the alternator cannot charge the battery. Same result, different cause.

To test both, get a multimeter. £8 Maplins. Same product, £20 Halfrauds.

Ignition on, don't start the car. 20 volt scale on multimeter. Black lead onto the engine block. Red lead into hole on the top back of the alternator. 12.6 volts, fuse fine. 0 volts, fuse buggered.

If 12.6 volts, while holding multimeter leads in same places, get a passing yokel to start the car. Voltage should change to over 13 volts. If no change, take alternator to auto electrician to prove its faulty.

The fuse is strapped to the underside of the chassis, drivers side, close to where the rear arm of the lower front offside wishbone attaches to the chassis. It is in a black fuse holder case about 35 mm long, in the middle of a thick wire. Replace with a midi fuse off EBay.

[JonathanT]

QBee said:

I don't remember the battery light coming on when the fuse went.
I do remember it coming on when the alternator failed on the back straight at Cadwell Park.

The light came on on mine both times the fuse had broken.

[Bassfiend229hp]

JonathanT said:

QBee said:

I don't remember the battery light coming on when the fuse went.
I do remember it coming on when the alternator failed on the back straight at Cadwell Park.

The light came on on mine both times the fuse had broken.

+1 ... definitely came on on mine too.

[QBee]

Bassfiend229hp said:

JonathanT said:

QBee said:

I don't remember the battery light coming on when the fuse went.
I do remember it coming on when the alternator failed on the back straight at Cadwell Park.

The light came on on mine both times the fuse had broken.

+1 ... definitely came on on mine too.

There We Are Then. Could be either.

[Bassfiend229hp]

QBee said:

There We Are Then. Could be either.

Very true ... but if it can be several things I usually try to start with the cheapest first.

[Digger]

Very much déjà-vu for me too, a few days ago. First time its happened for me.

[Mark.]

Bassfiend229hp said:

That's why you love me

[Mark.]

QBee said:

It's one of two things:
100 amp fuse
Alternator

Not the 80 amp in the footwell - nothing much would work if that one had gone.

I have had the fuse go twice, the alternator once.

I don't remember the battery light coming on when the fuse went.
I do remember it coming on when the alternator failed on the back straight at Cadwell Park.

The 100 amp fuse is between the battery and the alternator. If it goes the alternator cannot charge the battery.
If the alternator goes, the alternator cannot charge the battery. Same result, different cause.

To test both, get a multimeter. £8 Maplins. Same product, £20 Halfrauds.

Ignition on, don't start the car. 20 volt scale on multimeter. Black lead onto the engine block. Red lead into hole on the top back of the alternator. 12.6 volts, fuse fine. 0 volts, fuse buggered.

If 12.6 volts, while holding multimeter leads in same places, get a passing yokel to start the car. Voltage should change to over 13 volts. If no change, take alternator to auto electrician to prove its faulty.

The fuse is strapped to the underside of the chassis, drivers side, close to where the rear arm of the lower front offside wishbone attaches to the chassis. It is in a black fuse holder case about 35 mm long, in the middle of a thick wire. Replace with a midi fuse off EBay.

Thanks matey.

Just an update though - this morning it's all fine, no light on at all. Now thinking dodgy connection somewhere?

[Chuffmeister]

Definitely worth further investigation.

I would check the connections on the terminals within the small plastic 100A fuse box and change the fuse anyway (may have a crack in the fuse?). Also check the connections on the back of the alternator, the battery terminal connections, the connections on the starter motor where the live feed meets and for any breaks/ corrosion along the live feed itself.

You don't want to get a battery drain whilst you're in the middle of nowhere!!!

[V8 GRF]

Mark. said:

Thanks matey.

Just an update though - this morning it's all fine, no light on at all. Now thinking dodgy connection somewhere?

Everything you've described, light coming on, then off, not starting etc happened to me recently and it was the fuse which obviously still had a bit of contact depending on the heat. X-Works replaced it with one of the more substantial tagged 125amp fuses.

[QBee]

V8 GRF said:

Everything you've described, light coming on, then off, not starting etc happened to me recently and it was the fuse which obviously still had a bit of contact depending on the heat. X-Works replaced it with one of the more substantial tagged 125amp fuses.

+ 1. And don't just look at the fuse, take it out. More than one person has undone the two nuts and found they have a two piece fuse. It might make good contact when cold but be rubbish when hot.
In my limited experience, alternators tend to break down gradually. Again this may be temperature related.

[keith2.2]

Problems that go away by themselves, come back by themselves.

My battery light started to come on intermittently on startup and was staying on for longer and longer. Checked a few things and it turned out to be the alternator dying a death.