Does your battery light in your dash come on when the ignition is turned on ?
If it does then obviously the bulb is OK but does it go off when you start the engine ? Is there still a feint glow when engine is running. If there is then you have either a regulator fault or you could have a rectifier fault !!
If it doesn't then it can be either of 3 things. 1) the bulb is blown. 2) The wire feeding the negative signal to the bulb (other side of the bulb is fed with a + feed) from the alternator, is broken (open circuit) 3) the alternator isn't supplying the negative signal to the bulb when it is spinning more than 2500rpm, this is usually marked on the alternator as 'L'
Remove the wire from 'L' at the alternator and with your ignition switched on, short it out to ground - the bulb in the dash should light.
Also check your earth straps from your alternator to engine - engine to bodywork.
Also check, using an old 55W halogen bulb (or a 21W indicator bulb, but no smaller) whether you have a good +12v feed (approx battery voltage) to the back of the alternator. You may be showing +12v with a multimeter but multimeter's have an internal resistance of thousands or even millions of Ohms so using one will not show up high resistance bad joints/wiring within your system VERY IMPORTANT !!
RULE OF THUMB - never use a multimeter to check for +12v on a vehicle electrical system - ALWAYS use a high wattage bulb for a start and then a multimeter to check the actual voltage
Any one of these problems will cause the alternator to not be 'excited' into working and you would get the problem you are getting.
It's worth checking this out.
If it does then obviously the bulb is OK but does it go off when you start the engine ? Is there still a feint glow when engine is running. If there is then you have either a regulator fault or you could have a rectifier fault !!
If it doesn't then it can be either of 3 things. 1) the bulb is blown. 2) The wire feeding the negative signal to the bulb (other side of the bulb is fed with a + feed) from the alternator, is broken (open circuit) 3) the alternator isn't supplying the negative signal to the bulb when it is spinning more than 2500rpm, this is usually marked on the alternator as 'L'
Remove the wire from 'L' at the alternator and with your ignition switched on, short it out to ground - the bulb in the dash should light.
Also check your earth straps from your alternator to engine - engine to bodywork.
Also check, using an old 55W halogen bulb (or a 21W indicator bulb, but no smaller) whether you have a good +12v feed (approx battery voltage) to the back of the alternator. You may be showing +12v with a multimeter but multimeter's have an internal resistance of thousands or even millions of Ohms so using one will not show up high resistance bad joints/wiring within your system VERY IMPORTANT !!
RULE OF THUMB - never use a multimeter to check for +12v on a vehicle electrical system - ALWAYS use a high wattage bulb for a start and then a multimeter to check the actual voltage
Any one of these problems will cause the alternator to not be 'excited' into working and you would get the problem you are getting.
It's worth checking this out.
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