11 replies to this topic

[frosty90]

is there a way to test an alternator?

battery went flat for no reason and i think its the alternator

is there a way to test it before i change it?

[Ethel]

Measure the voltage across the battery when the engine is running at a fast idle. It should be about 14volts. If you don't have a meter you could just turn on everything electrical and watch the headlights to see if they dim, they usually brighten a tad if you blip the throttle. Poor wiring would fail those tests too.

[Ivor Badger]

Put a meter across the battery terminals and note the voltage. Start the engine and note voltage at tick over, rev up engine and voltage should be 13.8 to 14.6. The turn on everything and repeat the operation, the voltage above 2000 rpm should be in the 13.8 to 14.6 range.

Edited by Ivor Badger, 06 December 2009 - 11:35 AM.

[dklawson]

In addition to the two checks above, is the charge warning light working properly?

The light must...
1) be OFF with the key out of the ignition,
2) be ON with the key in the run position AND engine not running, and
3) be OFF with the key in the run position AND the engine running.

If the light is not working as described, replace the bulb and repeat the check of the above three conditions. The warning lamp is more than just an idiot light. If the bulb is not installed or working, the alternator won't put out the 14+ volts mentioned above.

If the warning lamp works as described above AND it fails the voltage tests described above, take it to a local shop and have it bench tested. They will confirm if it is faulty before you invest in a new or reconditioned alternator.

[frosty90]

have changed the alternator, but now the ignition light is still slightly on when driving??

[frosty90]

the ignition light is only faintly on, would this mean that its still not charging?

[danie garry]

the light is slightly on???? sure its not a reflection off somethin else?!?!?
very confusing
is the light slightly on when u rev it a little

[frosty90]

its definatly slightly on, like a dim light, suggestions?

[danie garry]

is there some kind of short where the bulb could be getting a lil bit of power??

[frosty90]

not that i know of, but i did kinda flicker and then just stay on, so im unsure

[dklawson]

Charge warning lamp test:
Unplug the alternator from the loom.
Turn the ignition key to the run position. DO NOT start the engine. Is the light on, off, or dim?

If the light is "on" or "dim" you have a short in the wiring somewhere/somehow.
If the light is "off", you have an issue with the alternator you just installed.

Don't forget to plug the alternator back in when you've finished this test.

[Ivor Badger]

its definatly slightly on, like a dim light, suggestions?

Then it is definately not charging.