[Cobom]

Ok, This may be a basic electrical question, but it is for a 1999 Cobra - and I have found basic instructions for other Mustangs that did not work on my Cobra.

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. ??

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?

[helipilot]

your neg cable is bolted to your alt?

[Cobom]

No, The alternator is attached to +batt with a cable. I assume the alternator is grounded to engine block, and that the engine block is grounded to -batt.

Question is why do I have a voltage diff from across batt (12V) and from +batt to engine block (14V). I have driven this daily for 18 months - it is almost like the engine is not grounded?

[heavy metal]

i would recheck all grounds....and run ohms on the alt to bat hot wire....