Thank you for the info. It happens with the car running
I'll have to lay attention to the headlights.
Sent from my SM-G920V using Tapatalk
If it is happening with your engine running and the SWR is acceptable, then it's very likely a high resistance connection somewhere in your power feed.
Power for a mobile radio should be fed off the battery, not tying in anywhere else.
All your connections need to be tight and corrosion free. Could be you have a bad crimp connector somewhere. It doesn't hurt to put a touch of solder on those. Also, you have to pay close attention to the crimping. Some of the cheap hardware/auto part store "smash and pray" terminal crimpers do a poor job.
Check your fuse holder, too. Those can start to come apart.
All connections should be clean and shiny. If there is any corrosion, consider redoing the install, as if it's corroded in one place, it may be in others.
Grounding is important, too. Do not rely on just the negative power lead for your radio ground. I usually install all my radios with a dedicated ground connection direct from the radio chassis directly to body ground.