mustrmrk Posted June 20, 2015 Share Posted June 20, 2015 (edited) Oops. I made a bad mistake - one I know better than to do. I assumed black would be negative and red would be positive. Someone before me wired a connection to the house battery w/ a black positive. I was messing around w/ my battery and inverter and managed to reconnect it to the neg. side of the battery. I know, I know... House lights didn't work so I started testing and found the problem. Fixed and all is well - at least on the house side. After I got it all working properly, I decided to test voltage at the inverter w/ the engine running. I started the engine but the charge light didn't go out. I have 12.2v across the starting battery posts w/ the engine running. I checked all the fuses and the fusible links in the black fuse box to the left of the engine (facing the engine) and everything checks out fine. I am wondering what a dead short on the house side of the isolator could have burned out on the engine side of the isolator that would keep the alternater from charging, It's an 87 w/ 22RE and AOD trans. Got any thoughts or suggestions? Other than "don't do stupid stuff like that again", I mean... Edited June 20, 2015 by mustrmrk Quote Link to comment Share on other sites More sharing options...
mustrmrk Posted June 20, 2015 Author Share Posted June 20, 2015 On a related note, I just found the following link that actually makes sense to me. It's for a Bosch alternator on a Porsce 914, but I expect much of the theory is the same. Does anyone know if the 87 Toyota uses the warning light to excite the field in a similar fashion? http://www.pelicanparts.com/techarticles/914_alternator_troubleshoot/914_alternator_troubleshoot.htm Quote Link to comment Share on other sites More sharing options...
Maineah Posted June 20, 2015 Share Posted June 20, 2015 In the case of the Toyota no. The ign terminal does it is keyed to come on with the the ign. switch. The light is also part of the brake system warning I doubt if it's your problem but low brake fluid will cause the light to light. The diodes inside of the alternator do not like reverse current and I'm guessing that did them in. If you have a solid state isolator (it will have cooling fins) you may have pooched it but if it is a relay type you feed reverse current to the alternator not a nice thing to do to your alternator but I guess you have all ready figured that out. It is far cheaper to just to replace it and let some one else rebuild it. Check your voltage at the alt. "B" terminal (the big wire) and make sure it comes close to matching your truck battery voltage they are fused so maybe you just popped the fuse it will be one of the big ones and probably is bolted in you can't just pull it out. Quote Link to comment Share on other sites More sharing options...
mustrmrk Posted June 20, 2015 Author Share Posted June 20, 2015 (edited) Yeah, been doing more testing. Both battery terminals on the isolator show voltage appropriate for the charge state of each battery - house on charger shows 13.2, engine shows 12.5. Field wire to alt has been spliced into to feed what i assume to be the the E terminal on the isolator - haven't changed anything and it was working properly, so I guess that's been wired correctly. And the voltage at the alternator output is the same - 12.5. Can I put 12v on the field terminal to run a brief full field test to see if the alternator kicks in? Not sure how to test isolator w/o output from alternator. Maybe disc. all wires, put battery on A term and look for voltage on 1 & 2? Isolator is probably solid state - it has fins. Edited June 20, 2015 by mustrmrk Quote Link to comment Share on other sites More sharing options...
WME Posted June 20, 2015 Share Posted June 20, 2015 An alternator should be over 14v when running. Quote Link to comment Share on other sites More sharing options...
mustrmrk Posted June 21, 2015 Author Share Posted June 21, 2015 (edited) Got it. Does anyone know if I can do a full field test on the alternator to check that it works? Basically, depending on the type of alternator, you either put 12v or a good ground onto the field terminal of the alternator to force it into full output. If it doesn't pull down and start generating, it's the alternator. If it does, it's likely the external regulator. I had to do this on my 120A Balmar alternator on my boat once (the +12v version) and it worked like a charm. Edited June 21, 2015 by mustrmrk Quote Link to comment Share on other sites More sharing options...
mustrmrk Posted June 22, 2015 Author Share Posted June 22, 2015 I pulled the alternator and it bench tested okay. Now I have to get it back in there and look for what else is wrong. Sigh. Anyone know the best way to bench test a 4 stud diode type isolator? I know A comes from the alternator, 1 & 2 go to the respective batteries, and E goes to the alternator's ignition wire. I tested across all studs w/ my multimeter in "diode" mode but had nothing but open circuits. Does the E wire have to be energized for the isolator to work? Another thing I found is that the wire connected to the E terminal is not energized when the key is in run position. The engine fuse and all the fusible links checked out okay, so now I need to figure out why the IG wire isn't energizing. And the O/D light isn't coming on, either, with the engine running. According to my schematics, they're on the same circuit. The charge fuse is good, but w/ the key on, neither side of the charge fuse socket has 12v. Is it possible that the short damaged the ignition switch? Quote Link to comment Share on other sites More sharing options...
Maineah Posted June 22, 2015 Share Posted June 22, 2015 The solid state isolator is nothing more than 3 diodes there is no real magic inside. The B+ terminal goes directly to the alternator B+ the two batteries are terminals 1 and 2 it really does not matter witch one goes where. The E terminal is the exciter it is connected to a keyed circuit seems like many installations were connected to the wiper motor circuit because it was easy to find power there. So the wiper fuse would be a good one to check if you have no power at the E terminal the fuse may well be the OD light also remember when the OD is off the light is on. You must have power at the E terminal or it won't charge. Now you will have no power at the B+ terminal because the power from the batteries is being blocked by the diodes when the alternator is not charging. When the alternator starts to charge the diodes will allow current to flow from B+ to terminals 1 and 2 but not from them this is the isolation part. Terminals 1 and 2 will have power present engine off and it should be close to what your resting batteries are. Easy right? Quote Link to comment Share on other sites More sharing options...
Maineah Posted June 22, 2015 Share Posted June 22, 2015 If you metered between B+ and 1 and 2 both directions (+ - ) and they showed infinite resistance the diodes are open. Like I said it is possible you pooched the isolator but you still need power at the E terminal regardless. Quote Link to comment Share on other sites More sharing options...
mustrmrk Posted June 23, 2015 Author Share Posted June 23, 2015 Roger, roger. Or should I say "Rogah, rogah"? Can I put 12v on the IG (the E terminal) wire to see if the alternator pulls down w/o hurting anything? The red IG red wire comes out of a connector to a triple-tap riveted crimp-on terminal. One side goes to the alternator and the other goes to the E terminal on the isolator. Took the connector apart and tested the source side for voltage to ground w/ engine running - nope. Pulled the 7.5a charge fuse and neither side of the socket was hot w/ the engine running. The fusible links all show continuity and voltage at both sides. However, it seems to me that the problem is before the fuse - whatever supplies 12v to the line side the 7.5a fuse socket would appear to be where the problem is. I'll take another whack at it in the AM. BTW - thanks for all your help. Quote Link to comment Share on other sites More sharing options...
mustrmrk Posted June 23, 2015 Author Share Posted June 23, 2015 What a dumb a - -. The wiring diagram in my 2" thick 1987 Pickup Service Manual from Toyota shows blocks containing "Fuse - 7.5a Charging" and "Fuse - 15a Engine" right next to each other. Knowing the charging fuse was in the black fuse box under the hood, I assumed that the 15a fuse just below it was the engine fuse. With a freshly rebooted brain this morning, I searched for and found a photo of the label that's missing from my under-the-hood black fuse box. It said the 15a fuse was for the flashers. So I pop the fuse out, try the flashers, nothing, put the fuse back in, and the flashers work, confirming the photo. Sheesh. Having already tested all the other fuses and circuit breakers I could find under the hood, on a lark I looked under the dash on the driver's side. There, marked as plain as day, was one labeled "Engine", eliciting a great big Homer Simpson style "DOH!" along with several other phrases pulled from my "Appropriate Word Toolbox". Changed the fuse and everything, including the isolator, works as expected. I'm charging both the start and house batteries now. My apologies for wasting anyone's time.. Quote Link to comment Share on other sites More sharing options...
Maineah Posted June 23, 2015 Share Posted June 23, 2015 Good job. Quote Link to comment Share on other sites More sharing options...
Back East Don Posted June 23, 2015 Share Posted June 23, 2015 My apologies for wasting anyone's time.. Typically the discussions inform the community as a whole. So certainly not viewed as a waste of time. Anyone coming along in the future and doing a search will likely find this thread helpful if they have a similar question or issue. Quote Link to comment Share on other sites More sharing options...
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