1989 Cadillac Fleetwood FWD 4.5LT

Attempting to start my car, when I turn on ignition to turn the engine over, starter clicks once, (All inside lights turn on, but dimmed out), so I bought a new battery and at the same time I personally took off my starter motor, took it in to Nearest Autozone for free testing and checked out fine, slapped the starter back on along with new battery hoping it might work, but still just clicks
Was told I have a bad connection somewhere justdont know where to start,
And I cannot tow my cadillac anywhere due to parking break is on and will kot come off unless car is on and switched in gear, even jump starting wont work.
What should I do?
Where should I start checking?
Do not want to be charged hundreds of dollars to find out its a 5$ relay or something small,
Thanks