Automotive project...Transistors VS Relays

Hi. I'm working on a project for my car. The point is to completely replace the ignition switch with a Start/Stop button. Some of you may have heard of a "Smart Key" or "Keyless Access"? If you would like to read more, here is the link...

https://www.electro-tech-online.com/threads/help-building-keyless-access-for-automobile.87738/

Anyway, I am trying to design the hardware, and I am down to the last few components. I don't know if I should use automotive relays, or if there are transistors I can use instead. There are 5 wires that need to be controlled, so it will call for 5 relays/transistors. I attached a schematic so you can see what I am trying to do. I thought it would be a good idea to assume that each wire could see as much current as what the fuse is rated for. Also, I would prefer transistors over relays, since they are smaller and have no moving parts. Any suggestions? Thanks.

Kyle

Oops, here are the schematics...

The problem is that most of the car electric is wired the way that connection is done switching ground (chassis) to the consumer.

I would not recommend high side switching using transistors because of resistive losses. (P-channel MosFets generally have a higher RDS(ON) than N-channel types)

When switching low side you must remove all chassis connections and move them to the drain of an N-channel MosFet.

My suggestion: Stick to available good quality relays.

Boncuk

allrighty, relays it is! Thanks!