I like to use a "Micro Switch" brand DPDT switch with a roller contact arm. It's much more rugged than some of the other switches people try to use. You still need the relay, but it also needs to follow the OEM wiring diagram to function properly. The kickdown switch and the relay just replace the OEM parts that are scarce and expensive with more modern components. I use 60 amp Bosch-type relays, mostly because the wires in the connector plug are heavier and the connector is less likely to get damaged. One function of the kickdown switch is that it kills the ignition circuit momentarily to get a quick unload on the driveline, at least during the downshift part of the engage/disengage cycle. The driveline needs to be completely unloaded at least momentarily to allow the solenoid to engage/disengage, sort of like shifting a 2-speed rear end.
Jerry
