When I tried to start it both batteries were dead.

QUESTION:

I needed to move my truck to another location so I could work on the speedometer problem. When I tried to start it both batteries were dead. A battery charger was connect but with reversed polarity. Before I could stop it the charger was tuned on. I immediately turned it off and disconnected it. I've charged the batteries but now the truck won't start. I found a 10 amp fuse burnt (in a panel in the engine compartment). When I changed the fuse some light on the dash panel came on - in a dim state- and stayed on, until I removed the fuse. The truck won't start although it will turn over. The ignitor light does not come on any more. This is a 1999 E-450 cube van with a Power Stroke Diesel. Can you shed some light as to what might have happened to the electronics of the truck My biggest fear is the computer.

ANSWER:

Because you hooked your charger up backwards it likely you blew one of the fuse links at the starter solenoid on the passenger side inner fender. I'm enclosing a schematic for the fuse links. Take a 12 volt test light and move down the harness where the fuse links are located and check for 12 volts. I suspect you have blown one or more.