Starter replacement?

Check battery earth and pos terminal clean & tight, I would still check or at least clean starter and check solenoid contacts, bench testing is not always fool proof.

This guide will help walk you through the steps

https://www.2carpros.com/articles/how-to-replace-a-starter-motor

Mark (mhpautos)

First if you have another key try that as the chip may be bad in your key then switch relay with a like relay to see if it's actually the relay or not.

Here is guide to help

https://www.2carpros.com/articles/starter-not-working-repair

and

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Check out the diagrams (Below). Please let us know what happens.

There is no ground wire for the starter.

And the small wire (probably purple) is not supposed to have power after you let go of the key

That would do it.

I don't have any experience with resetting the security on a GM.

You should post a new questions describing what the car is doing and that the security light is flashing.

In the mean time, i'll do some snooping for an answer too.

I've got some more info

General instructions on pass-lock relearn:

So the engine cranks but it wont start? IS the security light flashing? If so try this
GM PASS LOCK RELEARN- Ignition to "run" position, try to start and let key return to "run" position
Approx ten minutes security light will go off
Turn key "off" and wait 5 seconds
Repeat 2 more times for a total of 3 relearns.
Turn key off, then start it

Starter is mounted on the engine/tranny mid of car in front
it looks similar to that
it mount on by two bolts
make sure you
Disconnect the battery negative before any work
starter wired straight to the battery
and series damage can be caused to you or the system if wires touch ground or tools that is grounded

Disconnect negative battery cable.
Raise and support vehicle. As required, remove nuts from A/C compressor, exhaust system and/or engine braces, adjacent to starter.
Remove other items that may interfere with removal of starter.
If necessary, remove nut from engine cross brace. Using pry bar between upper engine mount and engine, pry rearward and support engine.
If necessary, remove oil filter, air induction tube and cooling fan.
Disconnect wiring at starter, and note position.
Remove starter mounting bolts and any shims.
Remove starter.

Installation

Before installation, ensure pinion-to-flywheel clearance is.020" (0.5 mm).
Add or subtract shims as necessary.
To complete installation, reverse removal procedure.
Tighten mounting bolts

Some of those shields have a small 10mm bolt opposite of the starter on the front of the trans. You will have to look up betweent the trans and engine to see it.

Not for something like that. There is another one facing forward (radiator)on the trans, above the starter bolt

If you lie down under the engine, you will see it towards the front of the engine, just a few inches off of the radiator. You will need to remove a flywheel cover (2 bolts) and then you can remove 2 mounting bolts for the starter. Keep in mind that you have two bolts on the starter body that need to come out as well.