mobilehippo Posted August 17, 2014 Share Posted August 17, 2014 I have 1978 Odyssey. I was driving back from a short camping trip and went to stop for some gasoline. Turned down my a/c and brought her into station. Filled her up. Started her up and noticed something wrong. The CHG light started glowing when I started her. Then I noticed that even though my emergency brake was engaged, the light was off. Also my gas gauge wouldn't go up correctly. I was still able to start her and drove her back 30 miles but the CHG light was on the entire time. I have no idea what's going on. The alternator is a year old so I don't think that's it. Most of the electronics is working, like the radio, turn signals and such when I drive with her. The A/C though is definitely not working though but it was also changed replaced last year. Could it be the belts are lose? Was wondering if anyone could help me diagnosis! Thanks! Quote Link to comment Share on other sites More sharing options...
mobilehippo Posted August 17, 2014 Author Share Posted August 17, 2014 Maybe it's the voltage regulator? Quote Link to comment Share on other sites More sharing options...
zero Posted August 17, 2014 Share Posted August 17, 2014 Fuel gauge in the older trucks like your's rely on full system voltage of 12-14.5 volts to read correctly. So does the engine temp gauge. From what you describe - sounds like low voltage caused by the alternator not working. That can be caused by a defective alternator or a bad external regulator. The ignition system can work with voltage down as low as 8 volts so it would keep on running for quite a while. Quote Link to comment Share on other sites More sharing options...
mobilehippo Posted August 17, 2014 Author Share Posted August 17, 2014 Is there anyway to decipher if it's the alternator or regulator not working? Quote Link to comment Share on other sites More sharing options...
Derek up North Posted August 17, 2014 Share Posted August 17, 2014 Have you got a multimeter? Quote Link to comment Share on other sites More sharing options...
mobilehippo Posted August 17, 2014 Author Share Posted August 17, 2014 Have you got a multimeter? Yes I do. What should I do? Quote Link to comment Share on other sites More sharing options...
Derek up North Posted August 17, 2014 Share Posted August 17, 2014 Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 17, 2014 Share Posted August 17, 2014 I think yours is old enough to have an external regulator so if it is not charging it could be either. The newer ones had the regulator inside of the alt. so this makes the testing a little more complex. You might check the 15 amp engine fuse but I doubt it is the cause because a lot of other things would not work. Quote Link to comment Share on other sites More sharing options...
mobilehippo Posted August 18, 2014 Author Share Posted August 18, 2014 Hmm.. I'm hoping its the external regulator because its much cheaper to replace than the alternator.... Quote Link to comment Share on other sites More sharing options...
whyverne14 Posted August 18, 2014 Share Posted August 18, 2014 Well mine did that on our first trip. Why does the brake light come on with the charge light? Apparently just to drive you crazy and make you think it's something else beside the alternator. At least that's what it did to me. But it was the alternator. Now you might have to figure out why the alternator failed so soon. I hear some of those older alternators are real easy to fix. Just new brushes. If you know someone who does that. Quote Link to comment Share on other sites More sharing options...
zero Posted August 18, 2014 Share Posted August 18, 2014 Is there anyway to decipher if it's the alternator or regulator not working? Yes. The regulator sends field current to "excite" the magnets inside the alternator. Just takes a simple volt-check at the alternator field connection. If it's getting field-current but not charging - the alternator is bad. If it is NOT getting field current - the regulator is bad. Quote Link to comment Share on other sites More sharing options...
zero Posted August 18, 2014 Share Posted August 18, 2014 Here's the 1978 schematic for the 1978 showing the connections. Quote Link to comment Share on other sites More sharing options...
mobilehippo Posted August 18, 2014 Author Share Posted August 18, 2014 Oh dear... where is the alternator field connection? Quote Link to comment Share on other sites More sharing options...
fred heath Posted August 18, 2014 Share Posted August 18, 2014 My 1978 has an internal regulator. Sounds like your alternator is bad. Just replace the whole thing. Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 19, 2014 Share Posted August 19, 2014 Oh dear... where is the alternator field connection? It's the green wire. Quote Link to comment Share on other sites More sharing options...
mobilehippo Posted August 19, 2014 Author Share Posted August 19, 2014 Hello! I just did a basic multimeter check with my battery and when I turn the engine on, the battery will spike up to 15 volts. So I believe the alternator is working and perhaps the regulator otherwise the battery charge wouldn't have gone up. I don't know what this means exactly cause my CHG light is still on but maybe there is some faulty wiring going on. My A/C won't turn on and when I turn the knobs the CHG light glows very bright. I might have to take her into the shop I guess. Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 19, 2014 Share Posted August 19, 2014 Yeah it sounds like you have got some battery connection or grounding issues some where. Quote Link to comment Share on other sites More sharing options...
zero Posted August 22, 2014 Share Posted August 22, 2014 My 1978 has an internal regulator. Sounds like your alternator is bad. Just replace the whole thing. I don't know what you have but the Toyota factory wire-diagram book for model year 1978 trucks in USA and Canada are only shown with external regulators and 45 amp alternators. Quote Link to comment Share on other sites More sharing options...
5Toyota Posted August 22, 2014 Share Posted August 22, 2014 no 1978 was originally fitted with an internal regulator alternator. I have had three of that vintage Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 23, 2014 Share Posted August 23, 2014 Question what color was you plug in the back of the alt.? and was it round? I'm trying to get my head around this can't remember but I believe the external regulator had a round plug in and it was green. Quote Link to comment Share on other sites More sharing options...
5Toyota Posted August 23, 2014 Share Posted August 23, 2014 green yes I am thinking two wires or 3 not round the regulater plug is round I think and should be on the fender well a black box the org is mecincal viberater point type and you could buy a solid state type smaller and flatter . but I had better results with oem type used to use a bosch back then. the reg plug was green also but bigger. I think the regulater plug had as many as 6 wires Quote Link to comment Share on other sites More sharing options...
zero Posted August 23, 2014 Share Posted August 23, 2014 Came with 5 or 6 wire plugs at the regulator. The field terminal on the back of the alternator is marked "F." Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 23, 2014 Share Posted August 23, 2014 There were two types of external regulators one was electronic the other was a mechanical (internal relays) the solid state ones needed B+, ign, and field to do there thing pretty cut and dry if you had ign+ and B+ the field should also have power. The relay types needed stator voltage a long with the rest to work properly. They were a lot more of a pain to deal with. The field voltage is what controls the alt. output the greater the field voltage the higher the alternator output so if you have field voltage and no output the alternator is toes up. You can supply B+ to the field wire at the alternator (remove plug first) and it should charge full tilt like lots so turn stuff off like radio and lights and don't do it for long. Quote Link to comment Share on other sites More sharing options...
Vanman Posted August 24, 2014 Share Posted August 24, 2014 How high will the voltage go if you do that ??? john Quote Link to comment Share on other sites More sharing options...
5Toyota Posted August 24, 2014 Share Posted August 24, 2014 you could burn out stuff head lights I had a solid state go bad on a datson xternal type melted the fuse box I had to rework that . didn't lose anything else. am I right been a while there was a wire on the B termanl besides the three termanl plug. just rembered some of the reman alternaters had a little different plug bosch supllyed a adapter plug with short wires . Quote Link to comment Share on other sites More sharing options...
Vanman Posted August 24, 2014 Share Posted August 24, 2014 I have heard about 16-20 VDC with shorted diodes in the alternator. I have only had diodes go open in mine so reduced voltage.I miss the alternator/generator shop off market street, he had everything in stock and was so cheap I quit messing with 'em, just let him fix it. He had a dyno with a scope and could see diodes that were weak replacing them before they failed.john Quote Link to comment Share on other sites More sharing options...
zero Posted August 24, 2014 Share Posted August 24, 2014 An alternator on a car or truck can put out near 200 volts if wired right and run fast enough. Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 24, 2014 Share Posted August 24, 2014 Many years ago we had a Jag E type in the shop that had a regulator go bad it finally came to a stop after all the water was boiled out of the battery. We replaced the regulator and battery and thought all was well. Well it wasn't he was driving at night there was not a single bulb that was not burned out, the radio was toast and a couple of gauges so yes an unregulated alternator is capable of a lot of voltage.The battery can absorb a lot of voltage for awhile so checking the output is definitely a short term test only. GM's older internal regulated alt. had a small pin that you could short to ground through the case to do the same thing it allowed you to see if the regulator was bad or the alternator before you took it apart. Quote Link to comment Share on other sites More sharing options...
Maineah Posted August 24, 2014 Share Posted August 24, 2014 Yes stator voltage of 200+ volts AC is certainly obtainable and even something close to 40 volts DC before the diodes explode is possible also. Quote Link to comment Share on other sites More sharing options...
mobilehippo Posted August 24, 2014 Author Share Posted August 24, 2014 Just to update what was going on, apparently there was a bad wire that was causing the electricity to arch and overcharging the alternator. It blew a bunch of fuses and the regulator and I had to get the whole system replaced. Eugh, was very costly, but she is driving a lot better now... Quote Link to comment Share on other sites More sharing options...
DanAatTheCape Posted September 4, 2014 Share Posted September 4, 2014 pull into just about any auto parts store & have your alternator checked. Yes you can do it yourself with basic understanding of a multi-tester. most auto part places will do the test for free - the symptoms you describe all can be explained by a bad alternator. or you can keep driving - your battery will die soon. Quote Link to comment Share on other sites More sharing options...
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