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12.17v going in at pin 5. 11.79 going into bulb, 1.58 on the other side of the bulb. All taken with the key ON. Car not running

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We are getting somewhere now.

Assuming the 3-3.5 volt measurement on my working alternator is OK.that means the resistance of the bulb is too

high(try wiggling it around) or the resistance to ground thru the alternator is too low.

 

You can detemine which by comparing to mine.

Measure the voltage at the bulb w/the alt.plug removed and white/red grounded thru an 8 ohm resistor.

An 8 ohm resistor simulates the alternator well and gives around 3 volts at the plug.(I used a large rheostat)

 

If the 1.6 volts increases much,your alternators resistance to ground is lower than mine.

If the 1.6 volts  stays nearly the same your charge lamp has higher resistance than mine.

 

Seems sorta unlikely that anything w/the lamp changed since you had a working alternator.but,with

the overcharging,who knows.

 

More likely the relacement alternator is different somehow.

Test rig at the shop likely had a different amount of resistance on this wire.

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Or an easier way would be to measure the current on the white/red w/everything hooked up and compare to mine.

I`ll show you mine if you show me yours.

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better diagram

 

For XT but electrically excactly the same as any internal reg. EA alternator.

 

myself, and probably others, are tracking along and learning from the debate, thanks for wading through it.

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Car running.

At Alternator 1.61 @white w/red, 11.93 @white

At Battery. 12.14

At charge lamp, 11.62 going in and 1.62 out

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For furthur diagnosis we need a different measurement.

 

Either measure the voltages at the charge lamp again with the plug disconnected from the alternator and white/red

grounded thru an 8 ohm resistance or measure the current on white/red w/everything connected(suggested).

Haven`t measured mine yet,but,I am expecting something in the 0.5 amp neighbourhood.YMMV

 

I plan to pull the fuse and put the ammeter in its place.

Edited by naru

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The readings I took were with the car running and all hooked up, car all back together with all factory wiring

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The readings that I posted were car running and hooked up. Tonight I’ll take the same with the car NOT running and I’ll try and find an 8 ohm resistor

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Measuring the current thru the fuse location would be easier.

No resistor needed.

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12.56 at both sides of the fuse when key is on and plug on the alternator is disconnected. 1.7 when plugged in.

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12.56 at both sides of the fuse when key is on and plug on the alternator is disconnected. 1.7 when plugged in.

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Just pulled my alt off of my 85 and bolted it on. 3.5 at the plug. Started it up and it WORKS!!! 14.6 while running! So the Napa alternators that I got (all 3) only had 1.7v.

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That shows the NAPA one had too low resistance since post #11 or earlier.

Probably partially shorted field windings.

It would only start charging w/an abnormally high voltage/current at/thru L.

Surprising that 3 were the same!

 

Cheers

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