My 78 J20 burnt a wire from my alternator to my amp gauge, now disconnected, the battery won't charge. I'm in the process of running a new wire will that fix the problem? I'm also wondering what could cause the wire to burn because I really don't want to go through this again. Napa bench tested the alt. and said its good.
AK J20
It will not charge without that connected. It only has to rub on something metal enough to expose the insulation to cause it to short out, so you must be careful where the wire is routed.
Full current amp gauges are very rare in newer vehicles, and I thought they were out of use completely by 1978. Running full alternator current to and from the dash is a fire hazard due to the possibility of a short within the passenger area.
Just run a charge wire with a fuse or fusible link directly from the BAT terminal on the alternator to the battery positive. Size the wire based on alternator max output (for example a 63 amp alternator would use a 10 gauge wire and 14 gauge fusible link). Ground the battery negative to the alternator bracket and to the frame.
Then replace the amp gauge with a voltmeter that is connected to an ignition-on terminal in the fuse box.
Bruce
Just run a charge wire with a fuse or fusible link directly from the BAT terminal on the alternator to the battery positive. Size the wire based on alternator max output (for example a 63 amp alternator would use a 10 gauge wire and 14 gauge fusible link). Ground the battery negative to the alternator bracket and to the frame.
Then replace the amp gauge with a voltmeter that is connected to an ignition-on terminal in the fuse box.
Bruce
That type of gauge is just a fire waiting to happen. Sounds like you either had a short or the main battery connection was bad so that wire may have been trying to carry starting current. You are lucky the vehicle didnt burn. Just run a wire from the alt to main stud on the starter or the positive battery terminal and eliminate the AMP meter. As others mentioned a volt meter is a better option.
MADelectrical advises;_
AMP gauges at the dash are troublesome.
They should be by-passed, and then install a VOLT gauge.
AMP gauges at the dash are troublesome.
They should be by-passed, and then install a VOLT gauge.
Most newer cars have a fusible link or other protection to the fuse panel. If your older car doesn't have some protection you will be doing yourself a BIG favor by adding a fusible link or maxi-fuse.
Heres a picture of the Maxi-fuse on my '55 Ranchwagon.
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And once again that is just my 1¢ worth...
Heres a picture of the Maxi-fuse on my '55 Ranchwagon.
And once again that is just my 1¢ worth...
ammeters
1- The ammeter measures the current for entire vehicle except the starter.
2- If the current is flowing to the battery the ammeter indicates a + measurement. If the current is flowing from the battery the ammeter indicates a - measurement.
3- When the generator (alternator) is supplying the same amount of current that the vehicle loads require the ammeter will measure 0 .
4- An ammeter that carries the entire vehicle load will have an internal shunt resistor. This resistor will create some heating and cooling as the vehicle loads vary. This heating and cooling, over time, can produce terminal connection problems and then loose connections which then produce more heat and eventual burning and failure of the connection.
5- The meter is the problem.
6- Not all ammeters have internal shunts. GM, for example used the main accessory wire as a shunt.
See attached.
vicrod
1- The ammeter measures the current for entire vehicle except the starter.
2- If the current is flowing to the battery the ammeter indicates a + measurement. If the current is flowing from the battery the ammeter indicates a - measurement.
3- When the generator (alternator) is supplying the same amount of current that the vehicle loads require the ammeter will measure 0 .
4- An ammeter that carries the entire vehicle load will have an internal shunt resistor. This resistor will create some heating and cooling as the vehicle loads vary. This heating and cooling, over time, can produce terminal connection problems and then loose connections which then produce more heat and eventual burning and failure of the connection.
5- The meter is the problem.
6- Not all ammeters have internal shunts. GM, for example used the main accessory wire as a shunt.
See attached.
vicrod
Amp gauges
Ive personally never heard of a car burning up from a bad amp gauge. If wired right there should be no problem. To small a wire or to much altanater for the amp gauges might be the problem. Routing the wire away from heat sources and through the firewall with grommets is a must. I ran one with no problems for years.
Ive personally never heard of a car burning up from a bad amp gauge. If wired right there should be no problem. To small a wire or to much altanater for the amp gauges might be the problem. Routing the wire away from heat sources and through the firewall with grommets is a must. I ran one with no problems for years.
I don't know about Chrysler, but GM has used the wiring under the good as a shunt for the ammeter for many years. The GM ammeter is connected to the underhood wiring at two points and the ammeter is actually reading the small voltage drop between those two points. That drop in voltage is used to determine what to display on the ammeter. As protection there is also a 5 amp inline fuse where each wire connects the ammeter to the wiring, so very little current actually flows through the ammeter.
FYI - I also have an old VOM (voltage-ohm-milliammeter) that has its own shunt on the end of the leads. Its just a small metal bar with a hole on each end, and the ammeter leads connect right next to each hole. If you connect the metal bar inline with the lead from the alternator it is supposed to measure the amps flowing through line.
Bruce
FYI - I also have an old VOM (voltage-ohm-milliammeter) that has its own shunt on the end of the leads. Its just a small metal bar with a hole on each end, and the ammeter leads connect right next to each hole. If you connect the metal bar inline with the lead from the alternator it is supposed to measure the amps flowing through line.
Bruce
Amp gauge
From the different Chrysler sites I checked cars prior to 75 had two problems, the firewall connector and to small gauge of wire for the amp meter. The connected corroded a lot and created connection problems(heat buildup). Some cars of the 60s thru early 70s had inadequate wirering to and from the amp gauge. Combine that with high output alts of the time and you have problems.
To solve that they put a resister in line that significantly reduce current in the lines. They also went with a shunt type amp gauge. This basically turned the amp meter into a volt meter. After 75 or so they went with volt meters. It was said the amp meter was basically a good unit. That being said the whole system was to blame. Is a volt meter better? It's up to the individual to decide. Me ide go with either. Wire both right and both will work, but I gained a little knowledge and that's a good thing.
From the different Chrysler sites I checked cars prior to 75 had two problems, the firewall connector and to small gauge of wire for the amp meter. The connected corroded a lot and created connection problems(heat buildup). Some cars of the 60s thru early 70s had inadequate wirering to and from the amp gauge. Combine that with high output alts of the time and you have problems.
To solve that they put a resister in line that significantly reduce current in the lines. They also went with a shunt type amp gauge. This basically turned the amp meter into a volt meter. After 75 or so they went with volt meters. It was said the amp meter was basically a good unit. That being said the whole system was to blame. Is a volt meter better? It's up to the individual to decide. Me ide go with either. Wire both right and both will work, but I gained a little knowledge and that's a good thing.
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