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Discussion Starter #1
Not sure what to think here. When I turn on ac fan, voltmeter drops to 10 and alternator light dimly lights up.
battery ignition off 12,6
battery car running 13.8
battery when ac fan switched on. 13.9 - 14
new alternator, battery 3 years old

Thanks for any thoughts here
 

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But Mad North-Northwest
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11,430 Posts
The A/C blower pulls switched power through the ignition switch. This is a lot of current. When the ignition switch gets old it builds up a bit of resistance, and pulling this much current though it can drop several volts on the switched side of the wiring.

A way to fix this is to wire in a relay for the blower. I modified the fusebox on my S4 to use an open relay slot and wired that up for blower power. Now the ignition switch triggers the relay, and the blower fan gets unswitched power from the fusebox. This solves the voltage drop issue.

See the thread below, particularly post #28, 49, & 51 where I explain how I did it. You've got an S3, not an S4, so it will require a different procedure but the idea is the same.

 
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