The volt meter on my Ram will only show about 10 or 11 and after a mile will fall to the far left side of the gauge(8).After cleaning all connections failed to change anything I removed the alternator for testing. The stud broke off so I bought a new Bosch unit. It worked well for a day ( about 20 miles) then did the same thing all over again. This whole thing also affects the shifting as the transmission only stays in drive, and will not downshift or go into overdrive.

What year Ram?

I ran into a similar situation on my '93,

It's a 2000 4X4.

Any chance the crank sensor is intermittent??? With no crank sensor, the system will NOT charge,the tach won't work, and you'll have no OD either. What bothers me is you say that the volt guage goes down to 8 volts.....Have you tried another battery/batteries??? Usually if a crank sensor goes, it will loose voltage slowly.....not drop dramatically.

I'd be checking charging output with a dvom at the back of the alt. The JTEC controller provides power to the alt field (blue), and a duty cycled ground (green). pretty cut n dried.

I replaced the crank position sensor a few years back, but that was because it would skip frequently at idle, but nothing else was wrong. After replacing it the problem disappeared.

Well...it's like J Body says...the PCM needs to see the "engine running" signal from the sensor to power the field circuit....You have some testing to do.

had an earlier 12 valve that the connector on the crank sensor rotted out, causing the exact problems you describe. hope this helps.

Old 12 valve totally different animal. Crank sense on those was soley to let the SBEC controller know the engine was running. 2000 VP equipped truck has two controllers. The JTEC controller on the firewall is the brainchild for the charging system. Cam and crank are present and engine starts is all done throught the ECM on the engine block.

When I had a problem with mine I believe I saw something about using an added voltage regulator. It's controlled by the computer otherwise. My net is really slow right now or else I'd find a link.

Is the grid heater staying on? I know on other equipment a bad grid heater relay will keep the heater on. The heater uses a lot of power and will exceed the output of the alternator and drain the batteries.