Percolator Coffee- Need Some Advice!

Recently I was at an estate sale in Fort Dodge.  It was the last day of the sale, and everything was half price.  I spotted a Corningware Cornflower 6-cup coffee percolator in almost new condition, so I bought it - for $2.50!

Today was my first experiment in percolator coffee, and I'm maybe doing something wrong, because the coffee was VERY bitter.  Maybe I'm adding too much coffee?  I used 5 heaping spoons of coffee for 5 cups of coffee, which was what the innernets had advised me to do.  Then I plugged in the pot, and was a little worried that the indicator light wasn't working.  Later I realized that the light  turns on when the coffee is DONE, not when you start the pot perking!

If you know how these vintage percolators work, please send some advice my way.  Thanks!