Okay, I need some help

Hey everyone.....
i have a problem with my 99 ford contour...
About 6 months ago we had the starter replaced and when we got the car back the battery wouldn't hold a charge.
I know that its either the the alternator or the alternator relay, because a friend tested the wattage and took the negative cable off of the battery while it was running and the car turned off.
How can I tell which one it is?
Can I replace the relay without replacing the WHOLE alternator?

Secondly.
We charge the battery in our home and it runs about an hour. We have 2 batteries that we alternate inside the car.
One day when we were switching out the batteries, we got in the car and the turn signals and the brake lights no longer worked.
We check the fuses under the steering wheel and the one for the brake lights was fine, (I replaced it just in case)
And still no turn signal or brake lights....
Anyone have any ideas Why these would go out all at once???

Thanks for any and all help from you guys here. !!!!
Chrissy

You might as well start with the easiest and cheapest possible fix which is the relay. Its only about $6-7. Not sure where its located on the I4, but on the V6 its located on the wiring harness behind the rear valve cover. Pop off the cover and you will see it.

How old is the battery? Are the connections good? Need to check both ends of the battery cables. Use a meter and measure the voltage. A fully charged battery should be about 12.5 volts.

Call your local chain autoparts stores and see which ones offer free testing. Have them test your charging system and battery.

Disconnecting a battery cable while the the motor is running can cause the alternator to fail.

Use a test light or a meter to make sure power is going through the fuse(s). Check the multifunction switch. Check the brake light switch.