Mercruiser Alarm Warning System does not come on when turning the key

Please help! My Mercruiser Alarm Warning buzzer does not come on when turning the key.
I have a 2006 Bayliner with a Mercruiser 5.0L (Serial # 0W622338)

Here's a few things I've tried:
1. I have replaced the buzzer and hooked it up to the battery and it works.
2. I used my multimeter to test the purple wire (power) and tan/blue wire (ground) that hook onto the buzzer and found out I was not getting enough voltage.
3. If I hook up the purple wire (power) and a different ground wire onto the buzzer it works which makes me think I have a problem with my tan/blue (ground) wire.
4. I tested the continuity on the tan/blue (ground) wire and it passed

Any ideas of what I could do next would be greatly appreciated? Thanks!

The buzzer has power with the key on the circuit is completed through the Tan/blue when the oil pressure or temp switch close and apply ground to the circuit.

Thank you! I understand what you are saying. Could it be that the oil pressure or temp switch are not working and that's why I'm not getting grounded?

If they are not grounding they are working. If you have everything hooked up correctly, after you turn the key on with the engine off, the alarm should sound after a short period of time due to no oil pressure.