Alt.lite stays on
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Alt.lite stays on
I have a 79 F100 that the alt lite stays on while the engine is on. The battery shows a charge of 14+ while running. The battery doesn't discharge while setting. I haven't found any loose wire or connections under the hood. I've not been into the dash yet, but was trying to remember what activates the lite
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The light is not grounded. It actually hooks between the ignition switch power and the regulator. When the ignition switch is turned to run, but the engine is not turning(the alternator is not charging) the terminal on the regulator(terminal "I") is close to ground potential , so with ground on one side and ignition power on the other side, the light glows. When the engine is started and the alternator starts charging, the voltage rises on the "I" terminal to something close to 12v. Since the light then has 12v on both sides of it, then the light goes out.
I believe the wire going to the "I" terminal is lightgreen/red or red/lightgreen. Check this wire and make sure it's not rubbed through, since if it's grounded, the light will glow. If it looks ok, then unplug the connector on the regulator and see if the light still glows. If it doesn't, then I would suspect a defective regulator, even though it's charging. The only other possibility is the wiring has been messed with and it's wired wrong. Ford had two different ways to wire their alternators.
I believe the wire going to the "I" terminal is lightgreen/red or red/lightgreen. Check this wire and make sure it's not rubbed through, since if it's grounded, the light will glow. If it looks ok, then unplug the connector on the regulator and see if the light still glows. If it doesn't, then I would suspect a defective regulator, even though it's charging. The only other possibility is the wiring has been messed with and it's wired wrong. Ford had two different ways to wire their alternators.
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Dave, I've chk'd the wiring at the reg. and all appears rite. There is a short pigtail that comes off the I term. leading to the firewall cowling. I disconnected there and had 12 v. w/ign. on. It also has 0.1v coming from the reg. With the the eng. running I have 3 v. at the I term. The reg. has been changed recently. It appears to be a cheapo from O'Reilly's so it could be defective off the shelf. Thanks, Jim
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Dave, I've chk'd the wiring at the reg. and all appears rite. There is a short pigtail that comes off the I term. leading to the firewall cowling. I disconnected there and had 12 v. w/ign. on. It also has 0.1v coming from the reg. With the the eng. running I have 3 v. at the I term. The reg. has been changed recently. It appears to be a cheapo from O'Reilly's so it could be defective off the shelf. Thanks, Jim
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Thread Starter
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New User
Joined: Dec 2009
Posts: 7
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Dave, I've chk'd the wiring at the reg. and all appears rite. There is a short pigtail that comes off the I term. leading to the firewall cowling. I disconnected there and had 12 v. w/ign. on. It also has 0.1v coming from the reg. With the the eng. running I have 3 v. at the I term. The reg. has been changed recently. It appears to be a cheapo from O'Reilly's so it could be defective off the shelf. Thanks, Jim
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