When should the charge light illuminate/replaced alternator (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Joined
Oct 12, 2004
Threads
470
Messages
3,087
Hi everyone,
Yesterday while I was out running errands in my 87, I glanced down at the dash and I noticed that my volt meter was almost in the red zone. I quickly headed for home so as not to get stuck on the road, and fortunately I made it.
I checked the alternator output with a multi-meter, and it is totally dead. I have a re manufactured alternator that I will swap in tomorrow and be back on the road.
My question however relates to the charge light. At no point did the light illuminate indicating that I am having an issue with the charging system. What is the trigger for the light? I would assume that it should have come on at some point, right?


Thanks,
Zack
 
Does the charge light turn on when you first turn on the key? It should light up when the alternator stops charging. However if that light isn’t coming in when you first turn the key to the run position then it’s possible that the. I’ll. Is burned out.....and a burnt out charge light could also prevent the alternator from charging.
 
Update....
I last drove my 60 on two days ago, when I made it home with an alternator that was not charging. Based upon the advice above, I confirmed that the charge light illuminated on the dash when the key was put into the on position. The light lit up with the key in the on position so I started my truck, much to my surprise it was charging normally as per the dash gauge. Within a few short moments, it stopped charging and it was back to where I started two days ago.
I shut the truck off, and turned the key to the on position again, now the charge light was not illuminated.
At this point I looked at all the associated wires and I didn't notice out of the ordinary, and still no charge light with the key in the on position.
I was at a loss, so I just replaced the alternator with a re-manufactured one that I purchased from Rockauto. Once I replaced the alternator, seemingly all the problems went away. The truck is charging normally, and the charge light works fine.
So what is going on? Does the alternator trigger the charge light? In the literature the accompanied the new alternator, it noted all of the tests that the alternator went through, and one of the tests was a malfunction indicator light test, to which my new alternator passed. How would a bad alternator prevent the charge light from illuminating, with the truck either on or off?
When I was in the process of replacing the alternator, i hooked the wires to the new one before it was installed and even then the charge light worked fine.
What am I missing, I didn't know that the alternator could control the charge light.


Thank you,
Zack
 
The charge light performs 2 functions in old school alternators (with internal or external regulator).

a) it provides indication of the alternator putting out good charge by turning OFF.

b) it provides field current (the bulb acts like a resistor, one end of the bulb goes to +12V and the other end to the field wire). Since current is flowing to generate the field, the bulb lights up (one GOOD reason to not replace the charge light with a LED unit). Once the alternator is spinning (engine running) the field voltage rises and as it does the bulb has less voltage across it and goes out.

So, a healthy charge light bulb is critical to getting the alternator started up (excitation of the field).

And, yes, the alternator does 'control' the charge light :)

cheers,
george.
 
There's a 'Charge Lamp Relay' under the passenger kick panel... May be bad. NLA from Toyota and no substitutes that I know of. Try to find good used. Or if you're crafty, you might be able to substitute a generic relay ... Dunno.
 

Users who are viewing this thread

Back
Top Bottom