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Discussion Starter #1
Just got an 87 bronco with the 351 in it, i was told the alternator had been replaced and it does look new and there is a good battery in it.But the battery light is on and it stays on.I have only driven it home so i havent had much time in the bronco, but all the power windows work and it doesnt seem to affect the engine or anything. so im wondering if there is a defect in the alternator? Im really not sure where to start.
 

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If the wires to the alternator are not making a good connection, this can also occur. Remove, clean, and reinsert the connections.
 

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Discussion Starter #6
The drive home is about 13 to 14 miles, it still starts up fine.Im not sure if its running off the battery right now or what.I will take it to chekers and have the system checked.
 

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Its a good possibility the alt. is overcharging the batt. Sounds kinda far-fetched, but mine is doing that now. My 88 runs fine, no issues anywhere, get it up to bout 2k rpms and batt light comes on. Both alt and batt check out good at idle. Only at 2k+rpm will the batt light come on.

Put it on a volt meter and check it at idle and while revving. See what it does. "dabranco" has good point also bout voltage reg.
 

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It's definately something in the charging system. Throw a voltmeter on it at idle and you should see 13.8-14.4 Volts, if its less than that then youre running on battery. I'd start with connections, then move onto the rest of the above mentioned...
 

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Same thing happened to me when I did the 3G upgrade, took to zone for a test and replaced the regulator and all is well. I also had a nice fresh battery so. like you no issues. Have it tested and follow the suggestions above, good luck.
 

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penis
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My experiance with these are if the alt (ext. Reg.) is replaced you should alway replace the voltage regulator. Overcharging is gonna fry the regulator and alt. faster and may toast you batt.. Going to autozone and have them check is a good idea. Also check the wires from the solinoid, to the reg. and to the alt back to the battery if they are corroded replace/repair as needed check ground ALL OF THEM as well I fixed several ext. regulated fords that were overcharging by simply replacing cables and connectors.
 

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If you replace the regulator (mostly likely your issue), make sure you bolt it down before you plug it in. Otherwise you will damage it and actually probably 7/10 times blow it up on the spot.
 

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I drove my car over 60 miles on just a battery charge - batteries can last a long time. Trace the power wire off the alternator - it should go to a megafuse and then to the battery. Theck resistance with a volt meter from batter to megafuse, both sides of the megafuse and them megafuse to alternator. If all checks out it is the alternator or battery.
 

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I'm thinkin its over chargoing seeing he was able to drive it about 13 to 14 miles. Did ya get it checked out today?
A battery will run a vehicle for quite awhile if the alternator is shot. The RC or reserve capacity number on a battery is the number of minutes the battery can deliver 25 amps (which is what the average vehicle takes to run) Sooooo if your battery has a RC rating of 65, then you can drive on just the battery (without radio, etc) for 65 minutes until the battery reaches cutoff votage of 10.5 and stalls out. :thumbup
 

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I have the same exact problem....dashboard battery idiot light is always on..... where in the wiring harness did you find the problem?

I get 12.5 volts across the battery in the morning and 14.38 to 14.60 at idle.... my dash and headlights also "pulse" when running and the tach sometimes jumps around even thought the idle is smooth.....

Alternator is brand new from Ryan....Battery is one year old 650 CCA Delco... and checked out perfect by AutoZone... car always starts right away no problem.

hmmm.. clearly a wiring problem, bad ground or fuse problem...???
 
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