1976 M500 440 Dodge won't charge

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1976 M500 440 Dodge won't charge

Home > Discussion Forum > Mechanic's Corner - Electrical

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All Messages in Thread	Author	Date
1976 M500 440 Dodge won't charge	Bill Caughey	7-8-02
New Altanator, new voltage regulator new battery, new wires, but still won't charge. I have taken out the alt. and had it checked and it works fine, changed the voltage reg. 4 times, and tested all wires. IT STILL WON"T CHARGE. Please help
Re: 1976 M500 440 Dodge won't charge	Sam Watson	7-8-02
Bill, do this: buy a 12 volt test light,the kind with the long wire with an alligator clip on it. Connect the clip to a good ground and touch the probe of the light to the LARGE stud on the alt., the one with the red wire on it. Light should come on brightly---this shows that the circuit between the batt. and alt is good---this circuit includes the ammeter, a source of a bad connection on the older Dodges. If that circuit is OK, then turn the key on and check with the light for power at the small terminal on the alt, the one with the green wire from the reg. on it. If I rember your wiring, there is only one wire from the reg to the alt. If so, the light will come on, but will be dim. If that checks out, then move the test light clip to a ground on the alt and again touch it to the large stud, light should come on brightly as before. Come back with what you find.
Re: 1976 M500 440 Dodge won't charge	Jim Rugg	11-10-02
Gentlemen: Your discussion mirrors my own recent experience with my old 400 V-8 on my father's Dodge 1/2 ton Explorer SE. This truck is an electrician's nightmare. The ammeter on the truck has nearly melted down on several occasions. This past weekend, Nov 2-4, I spent taking apart the dash cluster to inspect the ammeter guage which from heat nearly melted the back of the cluster box. The connections were so poor in the guage that current wasn't going through the guage and as a result, none of the truck's electrical components would work. I've cleaned the connections on the guage and installed a brand new battery. Still, I suspect that the battery is being discharged slowly as the needle on the guage always indicates to the left side of the marker line on the guage in much the same fashion as Bill's. There is never a healthy charge on the guage and it bothers me that I cannot be sure about the factory guage. I'm thinking of replacing it with another from a wrecked vehicle but must admit that going inside the instrument cluster and tinkering is not my favourite passtime. On the other hand, it seems that sentimentalism should have its rewards if I should be so lucky as to get the needle on the guage to indicate a healthy charge to the right. Sam, is there any use installing a temporary generic ammeter guage as a kind of test of the factory guage? As you mentioned, the ammeter can be a source of bad connection and I can attest to that. In fact the connection of the posts inside the guage seems to be deliberately poor by design and I am told by one mechanic that this is the nature of all such ammeters. Is this done to assist the performance of the guage? i.e. is it necessary to the performance of the guage that the connections be a bit on the loose side? Jim
Re: 1976 M500 440 Dodge won't charge	Bill	7-8-02
Sam everything checks out except the green wire from the voltage reg to alt. On this alt. there are two small wires and one heavier wire from the batt. The two samll wires are marked flo on the alt. the green one goes to the reg. and the other is connected to several other wires that are hot when the key is on, one of which is the blue wire from the reg. So, on the alt the heavy wire lights the light bright, the green wire is dead and the other lights the light Bill
Re: 1976 M500 440 Dodge won't charge	Sam Watson	7-9-02
Bill, you have the "isolated field" type alt. In this design the reg controls the field ground with full batt current being fed into the alt field via the key. Make sure the reg mounting is very well grounded, even to the extent of running a light gauge wire from one of the mounting screws to the ground post of the battery. I'm assuming you're not seeing any indication of charge on the ammeter? Come back with what you find
Re: 1976 M500 440 Dodge won't charge	Bill	7-9-02
Sam, this worked. It is now charging. I thank you for your help. Bill
Re: 1976 M500 440 Dodge won't charge	Sam Watson	7-9-02
Bill, you're welcome, glad to help.
Re: 1976 M500 440 Dodge won't charge again	Bill	7-10-02
Sam, it is back. It charges, but will stop and then starts chargig again. It doesn't slow in charging, it just stops charging. Sometimes it wiil start again.
Re: 1976 M500 440 Dodge won't charge again	Sam Watson	7-11-02
Bill, do this,: with engine off, turn on every electrical device in vehicle, including lights. Note where on the Discarge side of the ammeter the needle comes to rest. Start engine,run at around 1200 RPM, depending on how long you crank engine, ammeter needle will either swing over to "Charge" for some time, or just go over for a brief period of time. After needle has dropped back, continue to run engine at around 1200 RPM, (all electrical devices still on), and note where needle comes to rest. If ammeter shows at or near"0" on the "Charge" or "+" side, then everything is working fine, your battery is fully charged, the alt has replaced the charge lost on cranking and is now supplying just the current needed by the electrical devices. If the ammeter shows, at any time, a discharge when engine is running at 800+ RPM, then there is a problem. Come back with what you find.
Re: 1976 M500 440 Dodge won't charge again	BIll	7-12-02
Sam, the ammeter reads slightly discharge with the lights on, running or not. The needle does not move when it is started. With the lights off it is on the 0, running or not.
Re: 1976 M500 440 Dodge won't charge again	Sam Watson	7-12-02
OK Bill, do this. Scrape a bit of the insulation from the small green wire, start the engine and hold at around 1000 RPM, connect your 12 volt test light between a good ground and the bare section of the green wire, should show charge on ammeter. If it does, then replace the reg as it's bad. If no sign of charge, then "full field" the alt by connecting a jumper wire to the bare section of the green wire, again start motor and hold at 1000 RPM, touch other end of jumper wire to good ground, if no charge, alt is bad. Do you have a volt meter with a 0-15 volt DC scale?
Re: 1976 M500 440 Dodge won't charge again	Bill	7-12-02
Sam, this seems like the same thing, once with a test light, once with a jumper wire. Is the green wire you are talking about the negitave wire from the reg to the alt? I did both and the ammeter needle does not move in either case. Can an alt work sometimes and not at other times? once in a while this old beast will charge.
Re: 1976 M500 440 Dodge won't charge again	Sam Watson	7-12-02
Bill, not the same thing. Here's how, in brief, an alt works. The heavy stationary windings, (there's actually a set of three seperate windings), are where the current is generated. The rotating part, called the rotor, is actually a rotating electromagnet, the magnetic field being generated by passing a small current through the many turns of fine wire wound on the rotor underneath the heavy iron outer segments. The alt produces AC, which is rectified into DC by six diodes inside of and to the rear of the alt. There are three positive diodes and three negative diodes, this way, you get full AC wave rectification. In your alt, to control voltage output, thereby controlling current output, the amount of current supplied to the rotating electro-magnetic field is controlled by the voltage reg. Your particular design controls the grounding of the field circuit by cutting resistance in and out of the ground circuit in response to electrical load demands, wheather it be to charge the battery or operate the lights or accessories.All that said, the two tests are different in this respect. In using the test light connected to the green wire, (which is the ground wire of the field circuit), we're using the filament of the bulb in the test light as a resister. If you had gotten an indication of charge when doing this, then I'd suspect the reg as being bad. By directly grounding the green ground wire, we'd cause the alt to produce maximum voltage and therefore, maximum design amperage(current) which is stamped into the alt near one of the "ears" on front. Aside from bearing or rectier failure---it'll still charge with bad rectifiers, but the battery will discharge back through them when the engine is off---the only other thing that wears are the field brushes that ride on the rotor. These are small carbon brushes with a connecting wire embedded in them. These wires are of such a length that they "tether" the brush so that when the soft carbon eventually wears away, the end of the wire is prevented from coming into the soft copper surface of the rotor's comutator surface, damaging it. When the brushes wear down enough, contact to the commutater is lost, there is no magnetic field, and therefore, no alt output. These alts are easy to disassemble, check, clean, and install new brushes. If you didn't "peg" the ammeter when you grounded the green wire, then it's the alt that's bad, if all the rest of your wiring is OK. I'm no great fan of Dodge gauges, that's why I asked if you had a volt meter, the one sure and quick way of checking the alt.
Re: 1976 M500 440 Dodge won't charge again	Bill	7-13-02
Sam, thanks. I can get a volt meter from a friend or I will buy one. I took the alt off and had it tested on a machine at a parts store about a week ago. It tested ok. That is why I ask if they can work and then not work. I will also retest the alt with a ground wire from the battery to the alt. Your help is very much appreciated.