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99 miata Alt. light problems

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#1
Bi11

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Having problems with alt.light staying on. Replaced alt. still on ,replaced iat still on. any suggestions? thanks  Found no codes but when I disconnect battery goes away for a short while?



#2
davew

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Could be the ECU, which controls the regulator.

Could be the dash cluster, which controls the light.

 

I have seen both.

 

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#3
Keith Andrews

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Disclaimer: I'm a driver not a pro. 

 

Did you look at the output from the alternator old and new.  I've replaced a bad alternator with a new bad alternator before.  Also be careful if your alternator is not working correctly the car can run very lean.


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#4
FTodaro

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Disclaimer: I'm a driver not a pro. 

 

Did you look at the output from the alternator old and new.  I've replaced a bad alternator with a new bad alternator before.  Also be careful if your alternator is not working correctly the car can run very lean.

Good advice it should put out about 14 volts.

 

after losing two alternators i started running a volt meter to keep an eye on it. easy to install. and worth while.


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#5
Bi11

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Put in a second alt. light still on . Put new ecu light still on . They were all putting out 15.5 volts measured at the battery not 14? has no dash mph or rev , there is track mate in its place



#6
Bi11

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Car not ruining lean ,took it to the dyne two days ago



#7
Diller

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If I remember correctly the alt light on the dash is a normal closed switch/relay. If the wire going to it is broken or damaged the light will stay on.

 

It is a good idea if you have a data system to track voltage over time. Can give you a heads up if your alt is heading south or you have some loose connections/grounds popping up.


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#8
Jim Drago

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Put in a second alt. light still on . Put new ecu light still on . They were all putting out 15.5 volts measured at the battery not 14? has no dash mph or rev , there is track mate in its place

The light is likely on as it is over charging .. it should be less than 15 volts.
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#9
Bi11

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Alt. light went off for no reason? Hope it stays that way. Jimmy  I will check the overcharging thing again and see if has changed . Thanks for all the help from all



#10
Keith Novak

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I was having alternator problems this year and after swapping in a new one, and then a known good used one, it didn't fix the problem. 

 

It was the kill switch.  Jumpered the kill switch by attaching the wires to the same poles and the voltage coming off the alt changed from 35V to 14V and the voltage at the battery went from 12V and steadily dropping to 14V.


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