Without the manual to check...I would say ..How much current is available from the alternator when both are on. Might not be a good idea to light both without knowing how much current your pulling from the alternator.
Also..keep in mind that on a rainy cold night when the heater and wipers are going and summer time your A/C comp clutch is locked on and your running fuel injectors and other stuff ..you are pulling mondo bits of current.
Remember.. The battery only starts your Rig...the alternator is what supplies 95 % of the Voltage and current to run everything.The other 5% is used to trickel charge the battery while your drive.
Fog's & Highs.......Could be a Recipe for a Smoken Hot Alternator.....Or..some red hotskie wiring.!!
So...yah gotta wonder why the engineers chose not to light the fog's and High's at the same time.
Sounds like and
F5 Question.....
