99 silhouette electrical problem

Been having an electrical issue with my van this last week. My wife drove through some water last week during a storm and that is when it stared. When driving the battery goes dead and the van quits running. Tested the alt. it was good. Tested the battery, it was abou 5 yrs old, replaced it. Went to napa to check the volts comimg out of the alt and battery and their testing machine said check neg battery cable. checked to see if it was tight and both ends are tight. tested the starter as well and i checked out ok. Seems like a short but trying to eliminate all the major things first. Anyhting else that might get shorted out if you ran through some deeper water? Any help would great. Thanks!

Are there any trouble codes?

If NAPA's tester said to check the neg cable, then maybe it is corroded inside and there is excessive resistance. I don't know how much resistance it should have, but you could check the ohms of the neg cable as compared to the pos cable. If the neg is substantially higher that could be your culprit. Otherwise there is the pass through plug for the fuel pump. It is underneath the van, just behind the drivers seat. There are 2 connectors, it is the larger of the 2 (8 or 10 wires, don't remember for sure).

Ended up being the alt. after all. went to an actual garage and they tested the alt. in the car. thanks for info.