Starter problems for 88 ford aerostar van 7 passenger. how do i know its the starter or bad connection?

Test your battery and starter by doing a voltage drop test. Put one test lead of your meter on the neg side of your battery, one on the positive. Check voltage. Make sure that you are actually connecting to the battery itself and not the terminal ends. Should read 12.8-13.2. Keeping the neg in the same location move the pos to the terminal end, engage starter, meter should read above 10 volts. Continue testing down the pos wire to the starter, checking voltage, until you find less than 10 volts. If the voltage is good at starter, have someone turn key to the start position, tap starter with a hammer. if starter engages , replace starter.