Charging system? HELP

[1980c10]

Just finished my h.o. swap. Drive the first 30 miles fine no problem nothin, stop and eat lunch. Come back out, and leave and my car is running off nothing but the battery. It dies in a few min. Jump it several times to get to autozone. They say its not charging so i buy a new alternator and have them fully charge and check the battery install everything still not charging.

Now to the question could the hot wire from the battery to the starter be grounding out causing it not to charge? Any ideas please help guys. thanks

[1987cp]

There are a few wiring snafus that could cause a properly-functioning alternator not to charge. I once embarrassed myself quite a bit by not realizing that this one wire needs to be hooked to a switched 12V source.

The positive battery cable is good if the car's electrical systems are operating, and if the car starts the starter cable is OK. However, there are a couple of fusible links in the stock charge wire that goes forward from the starter solenoid that will burn through if there's a major grounding fault, so that's one thing that's very easy to check for.

Just so we know what we're taking about, which model alternator are you using? If we know the model, we can dig up decent schematics pretty quickly.

[1980c10]

i dunno its a 91 grand marquis using stock style alt for it

[gadget73]

there are fuse links in the harness between the alternator and the battery. On a 91 I believe they are in the section between the alternator and the driver side fender. Possibly there is another one at the starter relay. Quick test for this, unplug the alternator plug, and stick a test light in there. You should see the light come on where the two large black/orange wires are, and on the smaller plug where the yellow wire is.

[1987cp]

Here's the charging schematic you'll need (2G alternator). Thankfully, externally-regulated 2G and 3G alternators make for simple charging circuits. The main charging wire is annoying because it goes across the front of the car and is bundled with the headlight wiring, and the switched wire's path does go through the headlight connector next to the coolant reservoir, but the circuit itself is still very simple.

As Gadget noted, if you unplug the two plugs on the alternator, you should see +12V at all times on the black wires and on the yellow wire. The green wire should see +12V only when the ignition is on, and of course there should be continuity between the two places the white wire connects. Any deviations from this schematic and you'll have a nonfunctional charging system.

[1980c10]

thanks for the help guys love this site get back with you tomorrow for update

[91waggin]

*coughcough3gupgradecoughcough*

[1980c10]

Fixed it the red and green hot in run wire was bad and autozone sold me a bad alternator. after a whole day of diagnosing. thanks for the help and the shcematic spell check? haha

[1987cp]

Good deal! Charging problems can be a major pain, but it's always nice once you get it fixed.

BTW, someone slap me for saying "externally regulated" in that post above. It might mislead someone. 1G is external, 2G and 3G are *internal*.