I just bought an 87T and am sorting through a number of electrical issues. The current one I am addressing is that when I put the key in, turn it to 'on' or 'ignition', I none of the electrical work- no lights, horn, wipers, digital dash, nothing. It will start and run. Nothing else works until I rev the engine and then the dash lights up and all the other systems mentioned now work and stay on, even when the engine goes back to idle.
I checked voltage at the battery (supposedly new) while car is off and am getting high 12s. When I start the engine and rev it, the voltage stays the same, maybe even dips with increasing rpm. So I know I have a week charging system (new alternator on order).
I put the battery on a charger overnight to make sure it's at full strength but it has not resolved the symptom. I am looking at the fsm electrical and looking for a relay that might be suspect. Fusible links are all good.
Anything else I should be looking at?
Thanks!

 

Update. I have installed a new alternator and it is still not charging. Now none of the dash comes on even whe n the engine revs. Voltage regulator?

 

Battery fusible link was the culprit. It did not appear to be blown but for whatever reason, it tested with zero continuity. I jumped it and the dash lights up as they should, accessories work and the alternator charges properly. Weird.

 

My first thought would have been cleaning the grounds but glad you got it sorted.