PLEASE HELP- ALTERNATOR PROBLEMS? - Ranger-Forums - The Ultimate Ford Ranger Resource

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Old 09-04-2015
Thread Starter
Join Date: Sep 2015
Location: Deltona, FL`
Posts: 2

So I decided to swallow my pride & ask for help so I joined this forum. I really hope y'all can help me. My boyfriend has a '98 Ranger 3.0L & we are having some electrical problems.

It all started one night when my boyfriend was driving it & all of a sudden his battery light came on, his windshield wipers stopped working, his headlights dimmed, everything was losing power. He just barely made it home after fighting the truck to stay on.

We decided it was a bad alternator, & we were somewhat right. We went & got a new one. & then another, & finally another. What are the odds that we got 3 bad alternators in a row? After installing the new ones, every single time we'd start the truck up & let it run for a few minutes, the battery light on the dash would come on. We have checked the alternator fuse, we checked the wiring to an extent but found nothing wrong, at least whatever is obvious.

I really don't want to keep looking into the abyss of this truck if I'm not even making any progress. Has anybody had this problem or does anyone know what I can do? I really need his truck back on the road so my truck doesn't have to bear all the wear & tear anymore, she already has way over 300,000 miles on her.

Thank you in advance!
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Old 09-04-2015
Join Date: Dec 2014
Location: Dallas, TX
Posts: 10
Are you re-using or replacing the Voltage Regulator along with the alternator?

Where are you sourcing the alternator?

In addition being ABSOLUTELY SURE that the charging leads from the alt to the battery are in good shape, have you checked your grounds carefully? Bad connection and the engine and main battery grounds can cause bad voltage drops or even prevent the alternator from being able to push through enough current.
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Old 09-04-2015
Thread Starter
Join Date: Sep 2015
Location: Deltona, FL`
Posts: 2
We are re-using the voltage regulator, I didn't even think about that to be honest. But we checked all the grounds. I should probably mention that his truck busted a couple of hoses beforehand & one was the heater hose. So I thought at first that the coolant had fried the first alternator but evidently that wasn't the case.
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Old 09-05-2015
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iTrader: (1)
Join Date: Jan 2014
Location: Vancouver, BC
Posts: 7,601
You need to spend $15-$20 on a Volt meter.

Set it for DC Volts, 20vDC if thats a setting.

Since the late '80/early '90 all alternators had the regulator built in, you can just change the regulator but when you buy a new alternator you are also getting a new regulator.

Key off Engine off
Test battery voltage
12.7 volts is a new battery
12.5 volts is a 3 year old battery
12.3 volts is a 5 year old battery and almost done
12.2 volts or lower is a bad battery, won't hold a charge very long
Your battery may be run down now because of the problem, you can still check voltages by following instructions below

OK, now test the alternator wiring
On the back of the alternator is the B+ terminal, it has a larger wire, touch Red voltage meter probe to this wire, and the Black Probe to Ground(engine metal)
You should read exactly the same voltage as you did at the battery.
If not Mega Fuse is blown, 175amp fuse located on the side of the engine fuse box, not in it.

Unplug the connector on the alternator.
There should be a Yellow wire, with a white stripe, same test as B+ wire, Red probe to Yellow wire, and Black Probe to Ground.
Should get exactly battery voltage.

If not, the 30amp Alternator fuse IN the engine fuse box is blown, but this gets it voltage from the 175amp Mega Fuse, so if that was blown then it must be replaced before testing yellow wire.

On the same connector you will see a Light Green wire with a Red stripe, this is the ON/OFF switch for the alternator.
It is also the Battery Light wire.
Turn on the key, engine off
Test this wire same as above, it should have battery voltage when key is on.
It most likely does since battery light is working.

Plug connector back in.

If everything checks out, then start the engine

Check battery voltage again
Should be above 14volts, but below 15volts, the is "recharge voltage" from alternator
If you see previous battery voltage, 12.3-12.7v, then alternator/regulator is not working

After engine idles for a few minutes battery voltage should now be down to 13.6volts, this is the "maintenance charge", it keeps battery charged but won't "cook it"/over charge it.

If you turn on the head lights and set heater fan to High, voltage will drop and then come back up to 13.6volts, thats the voltage regulator working as it should.

Last edited by RonD; 09-05-2015 at 12:22 AM.
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Old 09-05-2015
cheese_man's Avatar
iTrader: (1)
Join Date: Nov 2009
Location: arthur
Posts: 2,100
what you describe happened to my 07 ranger

there is a small wiring harness that leads from the battery , then under it and along the driver side inner fender well , the edge of the metal fender had chaffed the insulation and was grounding out the power lead
( there is no fuse on that lead to blow ) no charge was reaching the battery ( hence battery light )

the engine was now running off of battery power alone
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