Alternator Issues - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

TruBlu351 · 10-01-2004, 09:44

G'Day,

Alternator works fine during the day, nice 13-14 volts & charging.

At night, head lights drop it to 13 volts, BUT if I load it up any more (brake lights or wipers on), the volt meter drops down to 10-11 volts (discharge), belt makes a very light short screech. When the load is removed the voltage still stays on 10-11 volts and won't start to charge again (alternator cuts out for some reason). Stop car for about 20 min and everything goes back to normal until overloaded again.

Any ideas please?

T_Juggalo · 10-01-2004, 13:07

the screech could be a loose belt which could cause this

also there are diodes on the alt which when fail cannot keep up with large loads. I would have the alt tested by a local auto shop. not sure what shops do this where you are but here we have canadian tire, which does free electrical testing

!Gn|T|0n · 10-02-2004, 18:33

First try the easy stuff. How is the earth from the alternator casing to the block? It may read 0 ohms with a multimeter but the resistance (esp of a bad connection) will rise with larger currents like those imposed by lights etc. The alternator may still be regulating correctly but if there is a 2 V drop between the alternator case and the block / battery then you'll read 12 V or less at the battery. Run the car with lights, thermos etc etc on and measure the voltage between the alternator casing (select a clean, unpainted section of the case) and the negative battery terminal. Is there a voltage drop?

I'd also fix that slipping belt. A drop in alternator revolutions will reduce its ability to maintain 14.2V

Let us know how you go.

TruBlu351 · 10-03-2004, 04:14

Thanks guys. Thought the belt was fine, but on closer inspection its stuffed, so I fitted a new one and I'll give it a run.

Should the alternator (voltmeter on dash) still give 14.2V when I have everything loaded up on it? It shows 12V with everything on and ~13.5 unloaded. I might try replacing the voltage regulator.

It's only a single wire set up. One big positive going from the alternator to the + on the battery and a small wire going to the ALT charge light on the dash. I assume the ALT earth must be internal to the casing thru where it bolts to the block?

SVO 351 · 10-06-2004, 06:43

the alternator should read 13.8-14.2 with or without a load on it and i would be checking the voltage from the gauge inside try and find some one with a multimeter and put it across the battery.

TruBlu351 · 10-06-2004, 07:37

Everything seems to be OK now. The problem was a slipping belt. I always thought that the fan belt would squeel when it slipped and because it was intermittant I blew that idea off............anyway, works as advertised now and sits on ~13.8 volts.

Thanks guys.