I need some help with my voltage issues
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Elder User
Joined: Sep 2006
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From: NW Burbs of Illinois
I need some help with my voltage issues
I have an 03 with the 7.3. Lately my lights have been getting dim then then bright, randomly. Even going 70 down the highway with the cruise on. My volts when dim are at 13.9 and when bright are 15.9!
My batteries were both replaced a year ago and about 3 months ago I had both of my stock alts rebuilt by a very reputable shop. This started recently, what do you think is my issue?
My batteries were both replaced a year ago and about 3 months ago I had both of my stock alts rebuilt by a very reputable shop. This started recently, what do you think is my issue?
Posting Guru
Joined: Mar 2005
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From: Burnsville, MN
I suppose there could be corrosion in a wire or connector somewhere, but I would try unplugging each of the alternators, separately, to see if things stabilize. If so, the alternators could be fighting each other.
Postmaster
Joined: Apr 2006
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From: CA Bay Area
Other suspect would be alternator. Ford have pretty poor quality alternators and I replaced 2 of them this year. Made a mistake buying rebuild from NAPA first time.
Don't think it can be ground or cable issue, since with dual batteries everything is doubled.
I assume your truck works on one alternator and second alternator is for aux power? Do you have double battery banks?
Don't think it can be ground or cable issue, since with dual batteries everything is doubled.
I assume your truck works on one alternator and second alternator is for aux power? Do you have double battery banks?
Postmaster
Joined: Apr 2006
Posts: 3,524
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From: CA Bay Area
Other suspect would be alternator. Ford have pretty poor quality alternators and I replaced 2 of them this year. Made a mistake buying rebuild from NAPA first time.
Don't think it can be ground or cable issue, since with dual batteries everything is doubled.
I assume your truck works on one alternator and second alternator is for aux power? Do you have double battery banks?
Don't think it can be ground or cable issue, since with dual batteries everything is doubled.
I assume your truck works on one alternator and second alternator is for aux power? Do you have double battery banks?
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Elder User
Joined: Sep 2006
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From: NW Burbs of Illinois
Yeah I need to check out grounds but it's not bump related. It's very intermittent. Even tonigh I was idling in the driveway and it was pegged at 15.9 volts then after a few minutes, down to 13.8.
The alts are my for originals and they were completely rebuilt. They put out over 120 amps each. I suppose something could be wrong with them. I'll get them checked out.
It's just strange because a year and a half ago I had to replace my instrument cluster because of my radio and power windows not working and I'm having that issue again plus the cluster shutting down and the lights dimming. Could this all be related?
Today I bypassed the acc delay which is the part that's going bad in the cluster but the lights are still dimming. I dunno.
The alts are my for originals and they were completely rebuilt. They put out over 120 amps each. I suppose something could be wrong with them. I'll get them checked out.
It's just strange because a year and a half ago I had to replace my instrument cluster because of my radio and power windows not working and I'm having that issue again plus the cluster shutting down and the lights dimming. Could this all be related?
Today I bypassed the acc delay which is the part that's going bad in the cluster but the lights are still dimming. I dunno.
Lead Driver
Joined: Sep 2007
Posts: 8,180
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From: Scio, OR
13.8 is about right. Obviously 15.9 is too high. Your problem is either the regulator in one of the alternators, or possibly the voltage sense wire to one of the alternators is corroded or loose, causing the regulator in that alternator to see a lower than actual voltage and causing it to over charge. Unplugging the wiring harness to one alternator at a time might be a good plan. If the problem goes away, you will have isolated it to the regulator or or the wiring for that alternator.
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Elder User
Joined: Sep 2006
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From: NW Burbs of Illinois
13.8 is about right. Obviously 15.9 is too high. Your problem is either the regulator in one of the alternators, or possibly the voltage sense wire to one of the alternators is corroded or loose, causing the regulator in that alternator to see a lower than actual voltage and causing it to over charge. Unplugging the wiring harness to one alternator at a time might be a good plan. If the problem goes away, you will have isolated it to the regulator or or the wiring for that alternator.
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Postmaster
Joined: Apr 2006
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From: CA Bay Area
I doubt you have 2 alternators working parallel with no switch or insulator.
Playing with disconnecting wires on system that you don't know might bring you additional problems. I suggest taking it to qualified electrician.
And yes, I would suspect the truck electronics have a circuit protecting them from damaging 15.9 volts. Again -this is something qualify electrician should check. Burned out computers are not cheap.
Playing with disconnecting wires on system that you don't know might bring you additional problems. I suggest taking it to qualified electrician.
And yes, I would suspect the truck electronics have a circuit protecting them from damaging 15.9 volts. Again -this is something qualify electrician should check. Burned out computers are not cheap.
Lead Driver
Joined: Sep 2007
Posts: 8,180
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From: Scio, OR
These are the wiring diagrams for both alternators. They are very simple with built in regulators just like the single system. There are no switches, insulators or isolators.
The only difference between this and the single alternator setup is that the I circuit on the single alternator is connected directly to the instrument cluster, where with dual alternators the I circuits are connected to the PCM. The I circuit is used to turn the alternators on and to light the warning light if necessary.
When you unplug an alternator, the I circuit is broken and the regulator in that alternator is switched off.
The only difference between this and the single alternator setup is that the I circuit on the single alternator is connected directly to the instrument cluster, where with dual alternators the I circuits are connected to the PCM. The I circuit is used to turn the alternators on and to light the warning light if necessary.
When you unplug an alternator, the I circuit is broken and the regulator in that alternator is switched off.
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Elder User
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From: NW Burbs of Illinois
Yeah there is some type of safety in there because now my accessories are cutting out at certain peaks. This has come at a terrible time since Thursday I have ti drive 700 miles round trip to trailer my brothers car that's been a whole logistical nightmare on it's own. Arg. Wish me luck as I now have no time to inspect and fix before my trip.
Postmaster
Joined: Apr 2006
Posts: 3,524
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From: CA Bay Area
Not likely both alternators have bad regulators. You might want to disconnect the heavy wire from one at the time and observe if the voltage stabilize? The charging light might come on, but having a gauge you can monitor the voltage.
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