Wiring for a engine stand

you can either wire the starter button "hot" to the battery or through the power/ ignition switch. You might want to be able to bump the starter with ignition off, like setting timing or adjusting valves.

Some comments on Bosch relays. Be careful of the coil wiring. This is because most of them have a built in spike diode, and if you wire the coil backwards you will blow up that diode

Also there exists a couple of variations on some "high current" ones. Some have 87 and 87A as one contact, and (that is normally open, there is no normally closed on those) and so the two terminals handle the extra current of the heavy duty contacts

Still others have LARGER pins to accomodate the larger contacts and those type will not fit a standard socket

Here's a good read EXCEPT that some of the diagrams reverse the coil grounding on 86/85 so be aware

https://www.electricalrebuilders.org/techlib/tech_articles/four_uses_for_relays.pdf