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I’m new to this Subaru forum. But touching on this older post. I have an 84 1800 gl, and it’s not charging. Put new alternator in, new battery, all new battery cables and grounds, new fusible links. Test the fuse on the fuse block and I have battery voltage on power side of block with fuse in, test the other side of block and there is nothing. But when I remove the L plug I get voltage on the other side of the fuse. This is a real humdinger to me


 

 

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Voltage MUST be the same on both sides of the fuse at all times.

Only way it can be different is if the fuse is blown or has a poor connection.

Fuse and charge light bulb must be OK in order to supply initial field current and  begin charging.

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You have a poor connection(high resistance) at the fuse.

This resistance is so much higher than the load resistance(the field coil+charge lamp) that all the voltage is lost at the fuse w/the circuit is loaded.

When you remove the plug the circuit is broken,there is no current flow and the high resistance at the fuse is of no significance.You measure full voltage.

Voltage at the white/red wire at the alt. plug(or both sides of the fuse) should be 12V  key on engine off w/ the plug removed,and about 3.7V plug in IIRC.

I say the charge lamp never comes on even though the bulb is good.

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But that is the thing the charge lamp does come on. And the gauge does work it reads about 7 volts even though the batter is fully charged. 

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I’ll take a picture of the dash with it running tomorrow morning. It is currently sitting at my shop with a charger on it. There are other dash lights that are on constantly, since this problem arose 

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I am not sure about 84, but 86 and up, it's not unusual for the alternator light to not light, and some of the others to glow when the alternator output is low.

Use a voltmeter, measure the volts directly on the battery, and also directly at the alternator output terminal to it's case while running.

 

 

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12 hours ago, Squidbilly503 said:

But that is the thing the charge lamp does come on. And the gauge does work it reads about 7 volts even though the batter is fully charged. 

The dash gauges are notoriously inaccurate,but,usually not that bad.

Since you already measured full battery voltage  at the charge fuse,the dash gauge reading is irrelevant for charging diagnosis.

You are measuring both sides of the charge fuse-correct?

Full battery voltage at the charge fuse w/key on engine off shows there is an open or high resistance somewhere in the field coil circuit.

No voltage on the other side at the same time means the fuse is bad.

Measure the voltage  at the white/red at the alt.plug.Key on engine off with the plug both in and out.

The inaccurate dash gauge is likely due to a poor dash ground.

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DAVET 

ive dome that and the battery voltage is 12.6v and tested the alternator but nothing is coming out except battery voltage. Took alt to four different places and all four had same output numbers.

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Naru2

so with the fuse in and the plug installed on the back of the alternator there is no voltage at the fuse. Remove the plug and there is power on both sides of the fuse. I thought that it was a contact problem in the the fuse. Removed fuse and cleaned contacts. Installed a brand new fuse. Still the same outcome 

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1 hour ago, Squidbilly503 said:

DAVET 

ive dome that and the battery voltage is 12.6v and tested the alternator but nothing is coming out except battery voltage. Took alt to four different places and all four had same output numbers.

I am not sure what you are saying here - You took the alternator out, and had places test it?

 

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5 hours ago, Squidbilly503 said:

Naru2

so with the fuse in and the plug installed on the back of the alternator there is no voltage at the fuse. Remove the plug and there is power on both sides of the fuse. I thought that it was a contact problem in the the fuse. Removed fuse and cleaned contacts. Installed a brand new fuse. Still the same outcome 

No voltage at the fuse w/the plug in means the high resistance is between this fuse and the battery.

FYI,from the charge fuse,the circuit goes thru a diode,the charge lamp,another fuse,the ignition switch and fusible link #2.

I would proceed by measuring voltage at the ignition coil + w/the plug in.The same fuse powers the charge lamp.

Good volts here confirms the second fuse,the ignition switch and the fusible link are OK.

That leaves the lamp the diode and the instrument cluster plugs(try wiggling them)

Unfortunately,access to the lamp and diode are not simple.I`d want to measure voltages there.

I`d suspect a loose plug first(could explain the low reading on the dash meter-did it go bad at the same time?)

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Check for a loose fusible link connection, it is a fairly common issue. They are located in a small plastic box mounted on the coolant reservoir.

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On 10/18/2018 at 8:12 PM, DaveT said:

I am not sure what you are saying here - You took the alternator out, and had places test it?

 

Davet

i removed the alternator from the car, took it to napa, car quest, autozone and an actual shop and had them test it. 

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I am interpreting that the places that tested it think it's working. 
Normal in the car should be around 13.8 V or into the 14s on the battery terminals with the engine running at a bit over Idle.  Over 15 is bad also.  At idle, the output can drop too low to charge.

If it tests good I would be looking at the wiring to the 2 wires on the small connector on the alternator - everything involved with them.
 

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