There isn't an ignition switch out there that will handle a starter directly, that is why they use relay's. The only type of switches you could use directly to a starter is the push-button type which has to be rated for very high amperage. Then you have to run primary battery cables to it. An ignition switch by design is only rated for around 15amps at most, this is one reason you should be running a relay. Starter relays are rated for around 100-150amps. The other and primary reason to run a relay for a starter to keep the primary battery cable as short as possible. Most vehicles have the starter relays located as close to the starter as possible, when you increase the length of your primary starter cables you are more likely to have high voltage drops. Those old direct starter switches were notorious for causing voltage drops to starters because they do not engage as good as a relay.
Just something to keep in mind.........

Mark D.

1968 W200 Sweptline
1969 D100 Utiline
1971 D100 SE Sweptline
1993 D250 Club Cab Sweptline
1986 W250 Cab & Chassis
1978 D300 Sweptline

E. Brookfield, Massachusetts