Wireless Access

First time setting up a master/local redundancy, local controller needs the Master switch MAC address? How do I find that or which MAC do I use? I figured "show inventory" but that lists more than one MAC i.e. HW MAC Addr : 00:1b:1d:01:a4:f8 to 00:1b:1d:01:a4:100

What type of redundancy are you trying to setup ?
For redundancy you can use the following :
- HA fast failover (Best option)
https://arubanetworkskb.secure.force.com/pkb/articles/HowTo/How-to-configure-AP-Fast-Failover
- LMS IP / BACKUP LMS
https://arubanetworkskb.secure.force.com/pkb/articles/HowTo/R-137
If you are trying tie the local to the master controller all you need is the IP address of the master and the IPSec key
On local :
Masterip <master IP address > IPSec <key>

On master:
Localip <local IP address> IPSec <key>

We currently have I believe a active/standby or active/backup both being masters with a VRRP between them. I'm labing up fast failover which has been successful but both were setup as master/master. Doing some research looked like master/local w/ fast failover seemed best as if im correct w/ master/local setup we wouldnt have to do config changes on two controllers just the master. Just wasnt sure how to setup the local as it asks for the masters mac address.

I see , follow the instructions I posted earlier to tie the master/local controllers

I just noticed that when the controller is fresh out of the box it during the startup dialog if you select the role of "local" controller it will ask you for the Master switch , I usually set it up initially as a master and then I point it to the real master 

To obtain the mac address you can run the show switchinfo: