[RichardJ]

The typical Bosch type relay draws 50 milliamps.

The typical ford type relay draws 10Amps.

The Ford relay can be wired a number of different ways, but it stills adds an extra 10Amp load on the battery while cranking.

The Bosch relay can really be only wired one way and that is to reduce the load on the ignition switch from the Delco solenoid. The hold-in winding in the Delco solenoid draws 10Amps while cranking. The Bosch relay carries that 10Amps and only puts a 50milliamp load on the ignition switch.

If your starter draws 300Amps and the Delco Solenoid draws 10Amps, why would you add an additional 10Amp ford relay to the battery load.

Think of this as like using a Bosch relay to take the current load off the headlight switch with the very popular headlight conversions.

You could actually use the ford relays to do the headlight conversion but I'm sure that doesn't need an explanation.