For the most part, the system wiring and connections are the same. The only wiring change needed pertains to the HSI unit. The KI-525 contained a Power flag instead of the standard Heading (HDG) flag as with the KI-525A. Therefore, pin P must be added to the existing KI-525 harness for the HDG flag in the KI-525A.
If the HSI is being upgraded to the -07 version of the KI-525A, then there is another pin that must be jumpered. Please see the KI-525A FAQ for more information on this matter.
The original KCS-55 system contained the KA-51A slaving accessory. This still can be utilized in the KCS-55A however it is recommended to upgrade to the KA-51B due to the age and lack of availability of service parts for the KA-51A. If the KA-51B is added, then a connector change would be required.