Originally Posted by TDCoffee
I bought one of those old school compasses, and the whole jeep frame seems to be magnetized so that it always points NW. It has a suction cup for the window, but there is no place it is free from the effects of the magnetism of the jeep itself. Anyone else find a place to put a compass?
Every car has this issue including the jeep. Some of the finer compasses have compensation magnets and an adjustment procedure to help you to adjust them. Cheap compasses don't have the compensation magnets and those will not work in most vehicles. The main issue in any situation where a battery of significant size is used is that as current is being drawn from the battery, metal that is adjacent to the wires becomes magnetized. This is especially true of the starter circuit because of how much current it draws.
Even boats which have a lot of fibreglass on them have this issue. And among boats, even sail boats are included. Most compasses for boats have compensation magnets to cancel the effect of external magnetism.
You could try one of the compensating companses.