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Alternator dash light

Joined
Jul 2, 2018
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20
Location
Perth
So i just determined that i have a bad alternating as my car was having trouble starting today. Charged the battery (externally) started it up and pulled the ground wire and it died. My question to you guys and girls is what triggers the battery dash light to appear. Why didnt it light up to show me the alternator was stuffed. I only realized my alternator or battery was cooked when my volt gauge was reading 9-10 volts. I know the bulb isnt blown as it lights up when the key is turned to the on position (prior to starting). Cheers for the help /ubbthreads/images/graemlins/smile.gif

**moved to newbie page
 

iceman69510

Turn Right Racing
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Typically the charge light is fed with 12V from both sides, one from the ignition and one from the alternator output. So when both are equal, no light. Ignition on (but car not running so not alternator output), 12V to ground through the other wire so light is on. If you are getting only 10V to the light, it should at least be glowing a little I would think.

You have a voltmeter to check actual output, and not rely on the gauge?
 
Last edited:
Joined
Jul 2, 2018
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20
Location
Perth
Ohh that makes sense as the light is alittle dull (when ignition is on, not car)
I did measure it with a voltmeter and it was reading at 11.3-11.4 volts while the car was running. Measured at the battery. How can i tell if its the alternator or the voltage regulator. As when i disconnected the ground from the battery, it ran for 2 seconds before it died. Thanks for the help
 

iceman69510

Turn Right Racing
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OK, you should see 14+ volt output when the car is running. Make sure the battery is charged before checking, as a low battery can cause the alternator to do strange things.

I would suspect it is your voltage regulator. But, as that is built in to the alternator (and trying to buy one separately can be as expensive as a reman alternator), you are better off replacing the alternator or going to a local rebuilder.
 

iceman69510

Turn Right Racing
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-Second comment. I don't recommend doing that disconnect test. The surges it can cause in the system can do damage to other electronics like modules. I would get that battery charged as I think it is too low to keep the car running right now. 9-10 volts is below dead. Really anything below 12.3 V is considered low and needs to be charged.
 

FlyingEagle

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Brushes wear out too, and can cause faint light inducing characteristics or just a solid light once it loses proper and tight contact on the stator slip ring area.

Charged battery and a working alternator will net you anywhere from ~ 13.4V to low 15V range with a super cold battery - anything outside of that range is a faulty regulator.

The voltage is temp sensitive and follows a chart that is posted in the FSM.
 
Joined
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Messages
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Location
Perth
I did charge the battery to 12.3-12.4 volts and the car started fine but only dropped voltage once running (assuming now has a load). Going to switch out the alternator tomorrow as i have a spare one. Thanks for the help. I think i saw a regulator online for around 50 AUD.
 

gtluke

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Sep 16, 2001
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4,210
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dirty jersey
do the saturn alternator swap, the mitsu alternators are poop. well new they were fine, but rebuilt ones are smashed turds, they last 1 year.
also make sure your o2 sensor heat shield is there and the power steering pump isn't leaking, those kill the alternator super fast.
 

FlyingEagle

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Quoting TheBen12345:
I did charge the battery to 12.3-12.4 volts and the car started fine but only dropped voltage once running (assuming now has a load). Going to switch out the alternator tomorrow as i have a spare one. Thanks for the help. I think i saw a regulator online for around 50 AUD.




Battery isn't even up to a decent percentage of actual state of charge when sitting at topped off 12.3-12.4, it would have to be much higher overall to indicate a proper state of charge. Be sure to test the battery and have it brought up to full state of charge before putting in and running the new alternator. Alternator internals like to take a shiz due to low charge in batteries and the Mitsu's are no different.
Battery cranked but alternator did not take over and you were running off battery voltage alone which doesn't last very long at the rate of amperage draw the engine and electrics require to operate with.
 
Last edited:
Joined
Jul 2, 2018
Messages
20
Location
Perth
Well i replaced the alternator and it does seem to be working now with around 13.8-14 volts. What voltage should the battery be at when sitting?? I might charge up the battery before i start driving it again. I really doubt its the battery as its only 3 months old. What i want to know is why the alternator broke. I was using the car all day and doing large amounts of driving, could excess heat from the exhaust cause the alternator to fry? Should i heat wrap the exhaust or buy/diy an alternator head shield? Cheers for the help.
 

thomcasey

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Sep 24, 2014
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Indianapolis, IN
Yes, heat-wrapping the exhaust can go a long way to keeping the voltage regulator from melting due to heat.
 

iceman69510

Turn Right Racing
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Alternators can die at any moment without warning. Heat can be either a slow of fast killer.
 

FlyingEagle

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I made all custom wrapping. DEI titanium/fiberglass style heat wrap was used and old heat shields from a Toyota Highlander that had the shields drop down and weren't repairable at the bolt up locations, but as a large sheet, it was mint to cut out and wrap around objects like my exhaust manifold and a second cover over the 02 housing, right beside the alternator.

Here is one of my alternator threads: Galant VR-4 Forums » Galant VR-4 » General VR4 Discussions » Alternator - which would you choose?
 

strokin4dr

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Aug 30, 2005
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2,770
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Savannah, GA
I have made some custom heat shields as well. Used the factory firewall shields off of a turbo mini cooper. They are easy bend and manipulate to the shape needed. The one I am using on my white VR4 is bolted in between my wrapped FP O2 housing and the GM alternator I installed last year. Seems to be working better than ever.
 
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