The indicator light does not illuminate when turning on cruise control.

No ABS light.

I have replaced brake switch, rear axle speed sensor, cruiser control switches and checked all vacuum and electrical connections.

Any places I should target for continuity testing?

1998 2500 5.9l 4x4 NV4500

Start by checking the fuse and for other non working electronics to find a common issue. Could be a bad circut due to corrosion. Activating the switch for a few times could loosen it up. There is a cruise control system check in a repair manual or fsm.

Cruise switches get a 5 volt signal from the PCM, and just modifies it, and sends it back. PCM does the rest. The buttons just route the signal voltage thru a selection of different resistors. Even if the brake light is on, the cruise light in the dash should still come on. See if you are actually getting signal voltage TO the switches.

Could be a bad switch

Check the vacuum hose. 95% of the time this is the issue. No vacuum, light will not come on. Move to the expensive stuff if the line is not cracked going to the servo that is under your battery tray.

PCM doesn't care if the cruise servo is getting vacuum or not. If you press the power button, cruise lite should come on. If it doesn't, there is an electrical problem.