# Alternator light

**URL:** <https://community.cartalk.com/t/alternator-light/57245>\
**Category:** Maintenance/Repairs\
**Tags:** 944, porsche\
**Created:** [November 6, 2010, 4:33pm UTC](https://community.cartalk.com/t/alternator-light/57245 "2010-11-06T16:33:27Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![motoslipstream](https://avatars.discourse-cdn.com/v4/letter/m/278dde/32.png) [@motoslipstream](https://community.cartalk.com/u/motoslipstream)\
**Post date:** [November 6, 2010, 4:33pm UTC](https://community.cartalk.com/t/alternator-light/57245/1 "2010-11-06T16:33:27Z")

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alt. light does not come on when ignition is turned on ; when motor starts alt. light comes on and pulses and brightens  
  
 with increase in RPMs. Battery voltage at  
  
 fast idle is only 10.5 volts when it should be approx. 13 to 14. Is this problem result of alt. voltage regulator ?

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<div class="post-metadata">

**Author:** ![shadowfax](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/shadowfax/32/13026_2.png) [@shadowfax](https://community.cartalk.com/u/shadowfax)\
**Post date:** [November 6, 2010, 5:21pm UTC](https://community.cartalk.com/t/alternator-light/57245/2 "2010-11-06T17:21:40Z")

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It could be. It could also be a bad battery. Have both tested. Many auto parts stores and (at least where I live) Batteries Plus will do that for free.