So I recently had my 1999 Disco 2 stall out while driving. Charged the batter up to 12.6 healthy and did a reading while car was running expecting something above 12.6 from the alternator but it when down to 12.2. Clearly the alternator was doing nothing to charge things so I check connections and belt and all was good so I proceeded to replacing with a new bosch alternator to find out the same behavior, no additional charge above 12.6. Any thoughts? Ground...How do I test that correctly? Will be very grateful for ideas on where to start. Thanks guys!

 

Have you verified the battery doesn't have a problem? Like a dead cell? Check all your grounds, and your main alternator cable. With a meter you should have 13.4 or higher at the alternator itself. If the main wire still shows low voltage = alternator isn't good. If you have 13.4 or higher at the alternator itself and only 12.2/12.6v at the battery then your cable from the alternator to battery is INOP. Make sure all terminals are clean and tight and verify grounds are clean as well.

 

Battery seems good at 12.6 but drops when car is on. Can’t get a reading of much at the alternator on both the old and new alternator hence why It certainly could be the D- ground but wondering what the test for that would be. Just continuity test to the battery negative terminal?

 

You are over thinking, start at the alternator.

Positive to the positive out and negative to the negative out you should be at 13.9 to 14.2 with nothing on but the engine
Positive to positive on the alternator and Negative to any ground should be the same
At the battery engine running with less than at 13.6 to 14.1 you have a wiring problem, my bet is either the primary ground or primary positive cable are damaged

 

on my 04 there is 2 ground wires that come off the negative, one bigger one goes to engine block and other smaller wire goes to the body 12 inches from battery, mine was lose causing high amps and that wire burned, i replaced it with a new wire, when thus was happening the ultraguage and my meter were showing under 13 volts, make sure your ground wires are tight and not corroded, also have your battery tested,

 

Sometimes this can be an issue:

Tech Tip: Flash the Field

If you’ve installed an alternator and it won’t charge, don’t remove it just yet. Here’s why: most Delco Remy alternators have "Auto Start" capability that doesn’t require a separate wire to excite the alternator to charge. During the manufacturing or remanufacturing process—when each alternator is tested for performance—a residual magnetism is generated in the alternator, so it begins charging as soon as the vehicle starts.

On rare occasions, the alternator can become demagnetized when it’s been on the shelf for a prolonged period of time. When that happens, the voltmeter indicates battery voltage instead of the typical alternator charging voltage.

Before you remove the alternator, first try to determine if a loss of residual magnetism is causing the loss of voltage. You can do this by flashing the field:

1. With the vehicle ignition in the “off ” position, remove the rubber boot from the alternator battery terminal and the rubber grommet from the small “R” terminal.
2. Take a small piece of wire and touch one end of it to the battery alternator terminal. Then touch the other end to the small "R" terminal. (Note: This may create a small spark, which is normal.)
3. Remove the wire and start the vehicle. The voltmeter should now increase its voltage reading to around 14 volts.
4. If the alternator isn’t charging, then re-check all connections and belt tension before removing the alternator.
5. Put the rubber boot and the rubber grommet back on.

Tech Tip: Flash the Field | Delco Remy

 

Remove ground cable at alternator bracket, clean and reinstall.

 

Continuity test between negative on alternator and battery and it failed. Ran a new ground and it passes continuity but still does not work. Literally zero reading from old and new alternator.

 

looks like you have a issue and its not the alternator, fun times with discos, i would check all the grounds and battery cables and battery

 

Ok so, turns out it was a combination of problems. The 150A fuse was blown and the alternator needed replaced. All was good for a day and then my daughter went over a speed bump and the dash indicator lights went on….then off…then the battery light came on and now the alternator is not putting out. Fuse is still good. So, I suspect a ground now. Where are they all located? Any other suggestions before I give up and take to a pro