Let's say I'm flying a cross country flight and I wanted to land in a Class D or enter Class C towered airport, but I lost my two-way communications radio but have my transponder squawking 7600. Should I blindly continue in and receive light gun signals to land or should I steer out the Class C and D and divert to a non-towered airport? In worst case scenario, what if my transponder is also out?
should I blindly continue in
First, never do anything "blindly".
The FAR and the AIM address the Class D question, so this part is the most easily answerable:
FAR 91.129 (d) Communications failure. Each person who operates an aircraft in a Class D airspace area must maintain two-way radio communications with the ATC facility having jurisdiction over that area.
(1) If the aircraft radio fails in flight under IFR, the pilot must comply with §91.185 of the part.
(2) If the aircraft radio fails in flight under VFR, the pilot in command may operate that aircraft and land if—
(i) Weather conditions are at or above basic VFR weather minimums;
(ii) Visual contact with the tower is maintained; and
(iii) A clearance to land is received.
AIM 4-2-13 (3). Transmitter and receiver inoperative. Remain outside or above the Class D surface area until the direction and flow of traffic has been determined; then, join the airport traffic pattern and maintain visual contact with the tower to receive light signals. Acknowledge light signals as noted above.
After that, 6−4−1 addresses more two-way comms failure actions:
a. It is virtually impossible to provide regulations and procedures applicable to all possible situations associated with two-way radio communications failure. During two-way radio communications failure, when confronted by a situation not covered in the regulation, pilots are expected to exercise good judgment in whatever action they elect to take. Should the situation so dictate they should not be reluctant to use the emergency action contained in 14 CFR Section 91.3(b).
Since "best judgement" is very situational dependent, the rest of this is subjective: I would not enter Class C, if there was another alternative. If you're already in Class C, and there are Class D/E/G airports available, divert. If you're already in Class C,and there are no other options, continue with the utmost caution (following the advice of the Class D procedures if able), using your own light signals to attempt to alert the tower.
Some "armchair lawyers" might even say that lost-comms (VFR) operations in Class C and even Class B could be conducted in the same manner as Class D, because each section starts with: "each aircraft operation in Class B/C airspace must be conducted in compliance with this section and 91.129."
I'd personally avoid B and C like the plague if I was VFR lost comms.