Alternator or fuse

[knk]

How do I tell if it is my alternator which has failed or the 100A fuse?

Coming back from the Wilton house gathering yesterday I noticed a the voltmeter was low, droppped lower and eventually car would not run. AA got me home by plugging in a power pack to battery.
Acumate plugged in overnight and still charging (orange light on).


And where is the 100A fuse?

Many thanks,

Kam

[Colin RedGriff]

I think if the 100a fuse goes the car wouldn't run, but not 100% on that.

The fuse should be on the chassis member near the starter motor, and there may be another in the loom in the footwell. At least that is what my '96 model has.

But as always - your's could be different :-)

[Johno]

You may find the 100A fuse is cracked, which will cause issues, rather than being completely blown/broken.

However this sounds like an alternator dying/dead or a battery dying/dead.

[GreenV8S]

Measure the voltage difference between the alternator output terminal and battery +ve. If there's no voltage difference, measure the resistance. If there's a voltage difference or resistance, the main fuse has failed or you have a wiring fault.

If the engine is running you can also do a similar test by measuring the voltage between battery +ve and -ve, and between the alternator main power output terminal and battery -ve. The battery voltage should be between 13.5 - 14V and the voltage at the alternator should be the same. You should also notice the battery voltage rise sharply (from around 12V to 13V+) as soon as the engine starts.

[steve-V8s]

The fuse (on mine) is attached to the underside of the engine mount bracket and is wired in the alternator output. If you remove the fuse or it fails the car will still run but the alternator will not be able to charge the battery. Follow the thick wire from the alternator down under the car and you should find it. Yu will need to get underneath so you will need to dig out the axle stands.

[red griff roger]

... and as it is only about 20p, may as well swap it while you are looking. And carry a spare. I know it is a small bit and you will lose it your tool box, but that isn't the point. If you have one, it won't blow.

[Chimjunkie]

Colin RedGriff said:

I think if the 100a fuse goes the car wouldn't run, but not 100% on that.

It does run. But will eventually run out of electricity...