[Cobom]

My battery has been dying. I checked the battery voltage before and during engine running - 12.5V approx. Should be 14V so I replaced alternator. Same problem. I do get 14V if I measure from positive batt to a engine nut.

I metered the + batt cable to alternator lug - 0.00 ohms. Negative batt to engine nut - 0.00 ohms. ??

The batt light in the dash comes on with key at ignition, goes off when started, there is a 5A fuse between light, gauge, green/red wire to alternator - it is good. I believe that is the exciter circuit - troubleshooting steps point to that - but then why do I get 14V at alternator?

With engine running I connected a jumper from negative batt to engine nut - sparked, engine noise changed pitch, voltage across batt increased to almost 14V.

Pitch in anytime and call me an idiot - but I thought the engine was grounded to battery - not the case? Should there be a voltage drop between neg battery and engine block?

[5.0rocket]

12.75 is a full charge for a battery, and yes you sould be putting out at least 14v, but you have to put the engine under a load. Turn everything in the car on,lights, wipers,radio,ac,EVERYTHING! touch your meter to the battery and get some help to run the rpm's up to 2grand and hold it there for 45sec to a minute. BY doing this your voltage under a load should not go below 10.25-10.50.

[snake 42]

Originally Posted by Cobom

My battery has been dying. I checked the battery voltage before and during engine running - 12.5V approx. Should be 14V so I replaced alternator. Same problem. I do get 14V if I measure from positive batt to a engine nut.

I metered the + batt cable to alternator lug - 0.00 ohms. Negative batt to engine nut - 0.00 ohms. ??

The batt light in the dash comes on with key at ignition, goes off when started, there is a 5A fuse between light, gauge, green/red wire to alternator - it is good. I believe that is the exciter circuit - troubleshooting steps point to that - but then why do I get 14V at alternator?

With engine running I connected a jumper from negative batt to engine nut - sparked, engine noise changed pitch, voltage across batt increased to almost 14V.

Pitch in anytime and call me an idiot - but I thought the engine was grounded to battery - not the case? Should there be a voltage drop between neg battery and engine block?

The normal output of your alternator should be 14 to 14.5 volts and there should not be a voltage drop between the ground lug on the battery and the engine lock. Sounds like you've got a bad ground connection somewhere. The fact that the engine pitch changed and the voltage increased points that way. Good Luck.