Am I right in concluding that I need to add pullup resistors to the high-side switch inputs so the switches will conduct adequate current to prevent contact oxidation? How much current is adequate to remove oxidation? I want to use the minimum necessary current because this will waste power and produce significant amounts of heat.

Hallo Lee,

yes, you always need a minimum current and voltage to make reliable contact. But, it's not only neccessary for preventing oxidation, but also for allowing to make contact, when there's dirt and moisture (!) on your contatcs. And even if contact is absolutely new, a minimum current and voltage is needed for making contact. It sounds absurd, but nevertheless it's true. It's interesting to note, that physics of metal contact is not well understood even today. When two metalls are contacting each other with not enough contact force, very strange things are happening at the interface. For reliably switching it's important to have enough contact force. But on the other hand, with too much contact force, contacts are heavily eroded by abrasion. So, certain compromises have to be done when fabricating a switching contact.

150mA gives a switching power of 12V x 150mA = 1.8W. That's a lot, of course. I would recommend you the following procedure: Have a look at the relais in your target car, and find that one showing the biggest coil resistance. As all switches which drive a relais are mostly of same contact material, you could use the biggest relais coil resistance found as pull-up.

Good luck,
Kai