QuinnG Posted January 17, 2018 Author Share Posted January 17, 2018 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 Link to comment Share on other sites More sharing options...
naru Posted January 17, 2018 Share Posted January 17, 2018 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. Link to comment Share on other sites More sharing options...
naru Posted January 18, 2018 Share Posted January 18, 2018 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. Link to comment Share on other sites More sharing options...
idosubaru Posted January 18, 2018 Share Posted January 18, 2018 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. Link to comment Share on other sites More sharing options...
QuinnG Posted January 19, 2018 Author Share Posted January 19, 2018 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 Link to comment Share on other sites More sharing options...
naru Posted January 19, 2018 Share Posted January 19, 2018 (edited) 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 January 19, 2018 by naru Link to comment Share on other sites More sharing options...
QuinnG Posted January 19, 2018 Author Share Posted January 19, 2018 The readings I took were with the car running and all hooked up, car all back together with all factory wiring Link to comment Share on other sites More sharing options...
naru Posted January 19, 2018 Share Posted January 19, 2018 For furthur diagnosis we need a different measurement. Link to comment Share on other sites More sharing options...
QuinnG Posted January 19, 2018 Author Share Posted January 19, 2018 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 Link to comment Share on other sites More sharing options...
naru Posted January 20, 2018 Share Posted January 20, 2018 Measuring the current thru the fuse location would be easier. No resistor needed. Link to comment Share on other sites More sharing options...
QuinnG Posted January 20, 2018 Author Share Posted January 20, 2018 12.56 at both sides of the fuse when key is on and plug on the alternator is disconnected. 1.7 when plugged in. Link to comment Share on other sites More sharing options...
QuinnG Posted January 20, 2018 Author Share Posted January 20, 2018 12.56 at both sides of the fuse when key is on and plug on the alternator is disconnected. 1.7 when plugged in. Link to comment Share on other sites More sharing options...
QuinnG Posted January 20, 2018 Author Share Posted January 20, 2018 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. Link to comment Share on other sites More sharing options...
naru Posted January 20, 2018 Share Posted January 20, 2018 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 Link to comment Share on other sites More sharing options...
Squidbilly503 Posted October 11, 2018 Share Posted October 11, 2018 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 Link to comment Share on other sites More sharing options...
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