Doesn't look like anyone has mentioned it but a bad ground can cause a lot to not work. Grounds are at the device end of things and if not making contact properly, they just won't work well. Later cars have both firewall AND core support grounds as well as the engine ground. That's no accident.
The little ground jumper on steering column handles horn and shift indicator lamp. I agree those other grounds at core support and firewall to block do need to be present.
