just cause you take the cable off the battery and it does not shut off it does not mean there is not a short in your Alt you car will keep running even if the Alt is only putten out 10.7+volts it might be going bad inside your alt.cause your battery light is only hook to the alt not the battery even if you have no ground wires it will not come on it only comes on if the alt is unpluged or is faulting...the only thing that will happen if your engine is not grounded it will heat up fast and then over heat

 

err wrong no engine ground no engine run. Go pull of the ground and watch it stumble and shut off. Engine has to be grounded to the chasis and the battry has to be grounded to the chasis to create the grounding surface. ECM is grounded to chasis if the battery is grounded the ECM isnt grounded everything shuts off. Battery unpluged means the alt is putting out just enogh to keep it idling. But your right on the alt could be going bad. Bad Grounds wont throe a battery light usually the Alt isnt putting out enough at higher loads.

 

TYpo ECM ISNT grounded to the chasis its grounded to the Block Block is grounded o the chasis they share the same ground pack.