Alternator Not Putting Out

13.8 to 14.2 is normal output for an alt. What makes you think you have a problem?

I agree, 13.8 is normal output as far as voltage goes. It's the amperage output you may need to check. Also replace the Voltage regulator if it's still got the old type, they're famous for crapping out.

The true test is to measure the battery voltage with the key and everything off. Then to start the car, turn on the headlights and rev the engine up to 1200rpm. Your battery voltage should be at least 0.5V higher with the engine running. Idealy it will be 1.0V higher.

D.Hearne said:

I agree, 13.8 is normal output as far as voltage goes. It's the amperage output you may need to check. Also replace the Voltage regulator if it's still got the old type, they're famous for crapping out.

Click to expand...

Ok sorry it was low amperage. Had the VR changed out at the same time as the Alternator.

There is an "energizer circuit" in the ignition that shoots a signal to the alternator, switching it on when you start the car. Both my 67 Stang and a 69 Econoline van I had , had this circuit go out for some reason or another ( never figured out why) My 68 Merc has now done the same thing. Only thing you can do then, unless you're an electrical engineer, is to run a jumper wire with a switch to bypass this. On my 68 Merc I ran a wire from the solenoid switch to the alternator. I don't recall what terminals I ran them to & from. There's one on the solenoid that's hot just when you start the car and the alternator? I think I ran it to the Stator or Field terminal, probably the Field one.

ok, mech. put new alternator on. It puts out 16 volts with bench test, 12.9 volts when I turn key to on, will put out 13.9 volts when I driving. If I turn heater on, lights on and radio on it will drop to about 12.4 vots.
Is this normal, also got the alternator guage to work now, so now I know if alternator is charging.

wiring is bad

If you get a chance run your car with everything on, heater motor, headlights on high beams, radio. Then run the engine at about 1200 - 1500 rpm for a min or so. Then turn the motor off and carefully touch the 3 wire harness from the back of the alternator and see if its hot. I had a similar problem before with this same thing. There is a bad ground wire now allowing enough amperage through the small wire. The secondary ground is from the engine block itself from the passenger side head to the battery - terminal.
To check for a bad ground wire using a pair of jumper cables connect one black clamp to the alternator, somewhere that the fan and belt wont hit and then the other end to the - battery terminal. Start the car and turn on everything and see if the alternator starts to charge higher similar to the readings on the bench. If so to fix the problem take the - battery terminal off from the motors side and clean it with sandpaper or a wire wheel / brush. Then clean the block. Then go buy dielectric grease, same stuff used on spark plugs. It helps the connection between electrical parts. If the alternator works good on the bench and not in your car this is your problem. If there is something that is not clear to you, you can e mail me at compsystems@adelphia.net

D.Hearne said:

There is an "energizer circuit" in the ignition that shoots a signal to the alternator, switching it on when you start the car. Both my 67 Stang and a 69 Econoline van I had , had this circuit go out for some reason or another ( never figured out why) My 68 Merc has now done the same thing. Only thing you can do then, unless you're an electrical engineer, is to run a jumper wire with a switch to bypass this. On my 68 Merc I ran a wire from the solenoid switch to the alternator. I don't recall what terminals I ran them to & from. There's one on the solenoid that's hot just when you start the car and the alternator? I think I ran it to the Stator or Field terminal, probably the Field one.

Click to expand...

sounds like your charge light burnt out. on voltage gague and charge light setups. keyed power is sent to the light the other end of it is on the I terminal on the vr. so basically its grounded when not putting out juice when its starts theres power there so it goes out, thats also how the vr gets signal to turn on the field.

ashford said:

sounds like your charge light burnt out. on voltage gague and charge light setups. keyed power is sent to the light the other end of it is on the I terminal on the vr. so basically its grounded when not putting out juice when its starts theres power there so it goes out, thats also how the vr gets signal to turn on the field.

Click to expand...

No, the light's not burnt, it comes on. The VR is a newer electronic unit.