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Alternator, Regulator or Both?

My 1982 Ford Granada has a separate, external voltage regulator. It’s not built into the alternator. After leaving the car sit in my garage for a few days, I discovered the battery was completely dead. I disconnected one battery terminal and, using an ohmmeter discovered the battery was connected to a short circuit draining it dead. I pulled the connector off the regulator and the short circuit was gone. I couldn’t reach the alternator connections because of engine compartment congestion. Here’s my question. Could the alternator and regulator be connected in such a way that the a bad alternator could short circuit the battery through the regulator? Could a bad alternator cause the regulator to fail? I would hate to replace the regulator only to discover the cause of the short circuit is really the alternator.

Auto electric shops likely have simple on-vehicle tests that can determine if the problem is the alternator or the regulator. The Ford service data for you Granada will have that information, so if you can get a copy of that, you might start there if you want to make it a diy’er job. Testing the alternator diodes for shorts too might be a good idea. That’s usually done with the alternator on the bench by measuring the resistance from the B+ terminal to the STA (stator) terminal, and from the STA terminal to the starter case or stator ground terminal. In both cases it should measure about 6 ohms in one direction, and high resistance in the other.

I think you might have a bum battery that is not holding a charge. I’m no electronic whiz but from my meager experience with multi meters, I don’t think the ohm meter is a good way to detect a short. There are too many other pathways and an ohm meter will only tell you if you have continuity on a pathway. You need to check voltage output of the alternator when it is running and need to check voltage at the battery after being charged and see if it holds a charge. You may have to just have these checked at a shop or parts store.

An alternator can be a drain on a battery. I had a GM alternator with internal regulator that did that. I was cheap and the car was junk so I installed a switch and turned it off when I parked the car. So much for really fixing things. There is no room under the hood of the Grenada.

My God! They still make parts for this car.

Isn’t Dave Ramsey still touting that car as the “go to vehicle” for getting out of debt?

I owned a 1975 Mercury Monarch back then(its sister car). Didn’t last 5 years in our Northern climate.

If you get the engine running a jumper wire to bypass the regulator

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will cause the alternator to run at maximum charge if all other wiring and components are functioning. If the battery is discharged running with the jumper installed for a while will do no harm but if allowed to overcharge the battery serious problems can occur.

The fusible link from the alternator BAT terminal to the solenoid terminal can burn out and go unnoticed. Many alternators and regulators have been needlessly replaced due to that link being burned. Likewise many alternators have burned up due to that link failing.

note- the jumper connects the F and A terminals on the harness connector.

I dunno but Dave thinks you can get a dependable old car for $1000 and that’s his limit on what to spend on a car if you still owe money. Like I said I don’t agree with some of his positions but know that he has helped folks in deep need of digging out of debt. I might be more inclined to concede a three year lease on a new car with a three year warranty for $200 a month while one is digging out. Dependable car for commute and new baby, guaranteed no surprise expenses, and after three years can reassess finances.

My mechanic replaced the alternator because it completely drained the battery when the car was not running. But he noticed the dashboard charge indicator light was on when the car was running although the voltage across the battery was measured at 14.3 volts. Should the external regulator have been changed as well? Although the voltage across it measured 14.3 volts, could the battery have been damaged to a point where it does not accept charging current?

My mechanic replaced the alternator because it completely drained the battery when the car was not running. But he noticed the dashboard charge indicator light was on when the car was running although the voltage across the battery was measured at 14.3 volts. Should the external regulator have been changed as well? Although the voltage across it measured 14.3 volts, could the battery have been damaged to a point where it does not accept charging current?

It does sort of sound like the external battery charging regulator is faulty. The regulator is what controls the charge light on the dashboard, and you mentioned it is on when it shouldn’t be. The battery could be damaged by overcharging or undercharging I suppose. Usually what happens in an overcharge situation is the liquid in the battery gets evaporated out and the battery goes dead b/c the liquid level is too low. A faulty regulator could cause an overcharge too. If you have the type of battery where you can pop a lid & see the fluid level, take a look how filled it is.

I should point out I’m just a diy’er and while I drive an early 70’s Ford truck that uses an external regulator of the mechanical type, I have no experience with fixing it, never has broken. I expect your car has a solid state regulator (transistorized) that fits in the same size package as my truck’s regulator, changing from mechanical regulator to solid state is what Ford was doing in that era. It’s certainly possible your solid state regulator circuit could fail 35 years later, what with all the heat, jiggling, and general abuse it gets living under the hood.

The alternator was replaced because it caused the battery to go dead when it was sitting? This doesn’t make sense to me. I suppose the alternator could have been shorted out but I fear either there is a short someplace else causing the battery to go dead, or the battery was shot so it couldn’t hold a charge, or the regulator was shot so that it was not charging the battery. I think its back to square one to check the condition of the battery, then check the charging system voltage to see if the regulator is working, and then check for a parasitic drain on the battery. Sorry.

If two of those diodes below short out, that could create a path to discharge the battery when the engine is turned off. For this to happen the two shorted diodes would have to be one from the first column and one from the second column .

Perhaps one of the diodes was already shorted and went unnoticed. Over time, another diode shorted causing the battery drain.

I’m of the opinion that any car using an external regulator should always have the regulator replaced along with the alternator.

As for Dave Ramsey, I kind of disagree with his suggestion to someone to buy a 1000 dollar beater until they’re out of debt.
Many of those people in debt have no clue as to how a car works or what it needs when they buy it. What good is a 1000 dollar car if the trans is on the way out or it needs 19 separate repairs to make it last a month; with said repairs not being noticed by the mechanically uninformed person buying the car???

Ramsey makes a lot of money telling people to spend their money wisely. What a novel idea… :slight_smile:

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I discovered what was draining my battery. After I recharged it and got the car started, I opened the trunk lid just a crack and noticed that my trunk light was on. Normally, my trunk light goes on when the lid is about half way up. The activation switch for the trunk light was stuck in the ON position. It went unnoticed because I was using tools from my garage and the trunk of my other car to troubleshoot the problem.

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At least you got a new alternator out of the deal. Paid for by you though. Not the end of the world to have a problem solved.

Thanks for letting us know the final resolution OP. Trunk lights and glove compartment lights not turning off are a common battery drain culprit. Good for you for getting to the bottom of it. Best of luck.