1990 Plymouth colt, new alternator, still won't charge. What tells alternator to charge battery?

1 may be alternator amp is low and load is high
2 alternator main +B to battery wire resistance to high

CHECK WIRING THIS UNIT WILL CONTORT THE FIELD IN THE COMPUTER. THE FIELD CONTROL IS WHAT MAKES IT CHARGE.

You would have checked the charging system before replacing the alternator, so I will assume the charging system is good.
If the battery is being discharged overnight or over a few days, you would need to disconnect it and check every circuit on the truck to find the drain.

Last time my van did that it was the alternator failing to recharge the battery.

your battery is probably junk. remove it and take it to your auto parts store and have it tested.

Thanks for choosing FixYa and welcome. Is the alternator new? If so, you need to check the connections and wires. Test them with a voltage meter to find out which one is not getting power. You could have a bad wire or loose connection/bad connection. It may be the alternator itself. If it is old, it will need changed. Make sure the battery post are cleaned and the wires have a good connection. Make sure the battery is fully charged. It won't charge up until you run the engine.

check ur starter if the car does not crank then thats what it is.

Hello and welcome to FixYa!

If the battery light is on, I strongly suggest that you have the battery charged. It can be an indication of a weak battery or a faulty alternator. If the battery light still on after charging then the problem will surely be on the alternator itself. If that's the case the alternator should be replaced to resolve the problem.

If the battery won't hold charge even on a new alternator then the problem will be on the battery itself. It surely is in the end of it's service life and replacement will be necessary.

You may try to reset it to by removing the positive battery connector, letting it sit for at least 5mins. then reconnect it again. This will reset the system and can get the battery light off.

Hope this helps and thank you for using FixYa! Have a good one!

Hello and welcome to FixYa!

If the battery light is on, I strongly suggest that you have the battery charged. It can be an indication of a weak battery or a faulty alternator. If the battery light still on after charging then the problem will surely be on the alternator itself. If that's the case the alternator should be replaced to resolve the problem.

If the battery won't hold charge even on a new alternator then the problem will be on the battery itself. It surely is in the end of it's service life and replacement will be necessary.

You may try to reset it to by removing the positive battery connector, letting it sit for at least 5mins. then reconnect it again. This will reset the system and can get the battery light off.

Hope this helps and thank you for using FixYa! Have a good one!

it could be a bad battery or you could have gotten a bad alternator.but if the battery is no good it d=wont charge the alternator.