My old legacy (2012 or so) 36v Terrova has lost spot lock, shows it has GPS on the remote but just has a long beep when anchor button is pushed. I have checked the basics, voltage, wiring plugs to all control boards, pairs with remotes. It will show and follow a heading. Any ideas where to go from here?

Have you tried to pair it? Sometimes it just looses paring.

No problem pairing with either remote.
I also have problems with controlling speed from remotes, which has made me resort to using the foot pedal most of the time.
I can verify the link to my Humminbird graph which indicates I-pilot link is working.
Does the I-pilot link in the head control spot lock?
Is there any information online to diagnose the control boards?

Sounds like the gps receiver is going out. That and the control board are no longer made. Sounds like time to update the motor.

Tested GPS is working fine, spot lock may work when first plugged in but if I turn it off I can't get it to work again.
Next i'm going to look at the electrical system from the motor to the batteries and verify everything is good before I spend big money on an upgrade.

Spot lock is working! After checking and updating the trolling motor plug and all the electrical which was sorely needed I disconnected the foot pedal and everything returned to normal. Spot lock and both remotes work as designed. I can just use it without a foot pedal but will take the pedal apart to see if I can find the problem anyway, for a spare.