Help - Dead battery and low voltage

[_Matt_ 42]

So a few days ago I noticed my tachometer going all whacky on the way to work, on the way home from work my car lost power and stalled, the battery was flat.

I replaced the battery and instantly thought the alternator was poked so I tested the voltage and it's about 12.3v when the engine isn't running and about 11.9v when it is. 11.3v under load.

I replaced the alternator with a second hand spare but I am still getting the same results.

Does anyone have any ideas what else could be causing the trouble? or is my spare alternator a dud too?

[polley 916]

sounds like dodgy grounds.

[_Matt_ 42]

sounds like dodgy grounds.

What grounds are you thinking of?

the original alternator had no ground wire going to the engine block but my spare did. Ill ground it to the block tomorrow and see if that makes a difference but the thing is bolted to the block in the first place so why would a ground wire be needed?

[hotwire 352]

Does the warning light come on with key & off when running?

Has the alternator got power on the main lead going to it?

It only requires these (& obviously earth circuit) for it to operate.

Assuming that wiring in order - it will be the alt

If the engine is cranking ok - it won't be an earth issue to the engine

[_Matt_ 42]

The Battery light no longer lights up. I earthed the D+ cable and my cluster light lit up so it's probably a dodgy alternator or regulator

[hotwire 352]

The Battery light no longer lights up. I earthed the D+ cable and my cluster light lit up so it's probably a dodgy alternator or regulator

Yup, well that (light not going) was giving you the answer in the first place

[_Matt_ 42]

A warning light that warns you by not working? That's a first for me haha

[hotwire 352]

A warning light that warns you by not working? That's a first for me haha

Yup, not going at all OR staying on. Both indicate a fault - hense me asking if coming on THEN going off.

Not coming on could be - ign supply to, blown bulb, wiring to alt, or open circuit in alt (worn brushes, open circuit rotor or regulator). Alt relies on circuit complete for excitation -assuming it is good.

Staying on - obviously indicating a fault too

[_Matt_ 42]

I've narrowed it down to the alternator so I'll be picking one up from the wreckers on tuesday.