Hi, welcome to JustAnswer!. This is Ed.
Check the crimp connections at both the positive and negative battery cable clamps for voltage drop.
The factory joined several cables together with nothing more than a heavy squeeze when they spliced cables from the positive side together, connecting the alternator output, starter, output to the PDC and battery into a neat little bundle that has no chemical fusion to one another. Given time, the individual cables may lose continuity to the others, sometimes connecting and sometimes not. When they don't connect together well, you'll get flickering in lighting systems and in the dash. Other vehicle owners may report tendency for the engine to stall, especially at idle.
While I've seen this situation mostly relegated to the positive clamp (see included picture), within the last couple of weeks I saw the exact same effect on a negative cable clamp crimp, which was my first. While this sort of thing can happen on either side of the battery, up until now it's always been on the positive crimp, so don't let your guard down.
My solution is simple if the cables are in good shape. Clean them physically and then solder the crimps to join them positively together. Remove the cable ends (they're bolted to the cables) to reduce heat sink, then heat and solder the crimps with a propane torch and rosin core solder. Flush the joint well with solder as it flows through the joint and drips out below to be sure you've reached all the copper that will accept the solder repair.