I agree that using 100k-ohm external pull-ups is PROBABLY safer than using =
1M-ohm pull-ups, that too is more speculation than anything in that my own =
tests have not been mass-produces and used in thousands of different cars. =
 Because no one has presented such hard evidence on why a given value of a =
pull-up resistor is bad in a car's noisy environment, the discussion then t=
urned to "well, why even use external pull-ups at all?"  I think that new q=
uestion is important, but I still am curious about the original question:  =
"HOW BIG IS TOO BIG when it comes to external pull-ups on modern PICs like =
the 16F1508 when used in 12-volt automobiles?"


You might be able to find some SAE guidelines on EMC that would tell you so=
mething concrete.
Car wiring tends to get conductive gunk on it and have leakages.=20
Ignition and motor noise, RF..
I once had a car whose rear wiper would kick off if I transmitted on the ha=
m VHF band at more than 10 watts.  Never did figure out why.=20
While the transmitter might not be in your car, you might be next to me in =
traffic.
Or a cop, ambulance, taxi, CB....

Can you do something other than dipswitches?  That seems to be the root of =
all evil here.=20
Maybe a second board with switches that you connect as needed through a SPI=
 interface or ?



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