Reply to "So, how bad is it going to be?"

Sissa,

If you have 13 volts at the battery, but only 5 volts at the starter, then there is a tremendous voltage drop somewhere, you should see almost the same voltage at the starter as you see at the battery. Five volts is not enough to crank the starter motor. Good troubleshooting.

Either one of the battery cable connections are dirty, or the contacts of the starter relay are more toasted than I am. There are 4 cable connections on a stock car; one at the battery, two at the starter relay and one at the starter. There must be a set of contacts in the circuit as well. A stock circuit employs the remote Ford starter relay, if your car has a newer mini starter, the contacts will be integral to the starter solenoid. However, the voltage drop is occuring prior to the solenoid.

Using your voltmeter, and the same technique you used to find the voltage drop at the starter, measure the voltage at each cable connection, one at a time, until you find where the voltage is dropping. At the battery, measure the voltage by touching the meter lead to the cable end clamp, not to the battery post.

You are close to having this problem solved.

Your friend on the DTBB, George