WST 4900FA turn signal problem

I got a 2012 western star 4900 FA, recently notice a problem that if the truck is running and headlight/ marker light it’s on, right side turn signal will not work, both front and back, and there’s a very dim turn signal light on the dash constantly.

Tested the voltage from the turn signal, between control wire and ground has constant 4.5 volt when turn signal is on, all voltage is normal if truck is off and headlight/marker light off.

Checked the ground is good, 2 ohm. The wiring near the front headlight and turn signal is good.

Anyone has similar problems or has ideas what is wrong?