truck does not turn over on 1990 Ford E-350

engine was cranking, voltage shows 14 plus volts, then it faded to nothing - smell of plastic, now no crank

Asked by for the 1990 Ford E-350
With the smell, I will say get the battery tested it may have blown a cell.
1 more answer
You need to replace both batteries and check all battery cables and connections. don't replace the batteries with cheap batteries.