Quote Originally Posted by mpgmike View Post
Just a shot in the dark; when I design a power supply for my PICs, I isolate the 5v (or 3.3 or whatever) regulator with a 10 ohm resistor from 12v (or whatever) and place a 10 uF and 0.1 uF cap on the regulator input side. Then I put a 100 uF and 0.1 uF (and sometimes a 0.01 uF) parallel caps on the output side (5v side) of the regulator. In addition, there will be some distance between the regulator and the PIC. The VCC pin(s) get(s) an additional 0.1 uF cap to help filter any spikes. These larger electrolytic power supply caps add reserve when a brief power drain occurs, and the small disc caps filter noise.
totally agree and in an automotive enviro would make that 10 ohm R a RFC .
also for high current switched loads pcb layout and wiring design are crucially important


I have a suspicion about what the problem is, but I can't confirm it without knowing more detail. I'm not going to go out of my way on this just for the chance to learn later that that's not actually the problem and the goal posts have moved again.