ALT warning light question
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
12 volts is applied to one side of the light, in the instrument cluster. The other side of the light runs out to the I terminal of the voltage regulator which is pulled down to ground at first. When you turn the key to RUN but do not start the engine, the light illuminates. When you start the engine and the alternator begins to produce current, the field relay inside the regulator jumps 12 volts over to the I terminal of the regulator. Since 12 volts appears on both sides of the light, no current flows through it and it shuts off to indicate that the charging system is functioning properly.
If the light does not work, try replacing the bulb. However, some aftermarket, non-OEM electronic regulators will not let the bulb come on at startup to begin with.
If the light does not work, try replacing the bulb. However, some aftermarket, non-OEM electronic regulators will not let the bulb come on at startup to begin with.
Thread
Thread Starter
Forum
Replies
Last Post
Larry85355
1973 - 1979 F-100 & Larger F-Series Trucks
4
Nov 13, 2008 04:28 PM
norvillebob
1961 - 1966 F-100 & Larger F-Series Trucks
9
Dec 6, 2006 07:23 PM
