I used a diagram from an automotive electrical website for those pin numbers on my crude diagram. Left the grounds off for now because I wasn't sure what to ground them to.

In the box I could use some sort of bus bar for the incoming 30A and another for all of the #1 pins.
https://www.accessconnect.com/car_relays.htm

 

Here is my latest, learned a little more about how to sketch stuff up in this application. Still not quite done yet.

Latest work in progress 12-3-2020

 

I might have simplified this down to four relays. Bonus! Power going to the speed selector switch now!

 

Nice sketch. I assume the (-) of the motor is connecting to the power strip too? Otherwise a 10-gauge just to power the relays is a bit overkill. On the plus side, once you're done you'll have got solid power and ground strip locations if you ever want to add anything else under the dash. For example an always on USB jack.

 

I left the motor negative off because I'm not modifying anything there, far as I know. Not even sure where its actual ground is. But added a ground on its negative side in the diagram, guessing it grounds to the chassis. Took the ground off the grounding strip since I will be running a 10 AWG wire back to the battery.

The Chrysler wiring diagram has 12 AWG going to the switch and the resistor pack. Not going smaller, and I have 10 AWG laying around. Not switching the relays with 10 AWG, just using it for the 30A service from the battery.

Plan on using a dual bus bar I saw at West Marine, I think it was about $19 but it was about as reasonable price as I've seen, shy of getting some plumber's tape and super rednecking it together. And yes, thought of possibilities of running extra stuff out of there if the ideas arise.

 

I looked closer under the hood, the wire that is in there from the old fog lights is not marked where I can see it. My gauge says it's 12 AWG. Will pick up 6' ea. of 10 AWG red and black at West Marine, the good tinned well marked stuff. Website says $0.89/ft.
Latest version:

 

Nice diagram!

 

Thanks.
If I have anything ready to let the smoke out in there I hope someone notices and comments.

 

OK, still collecting parts for this. However, here is where the project is going now.

Unused fuse slot 4 under hood is labeled 40A on the lid. Going to add a terminal in the box and run a 10 AWG red (probably) wire from it into cabin to the new blower motor relay box. Black 10 AWG from the box back to either battery negative or body.

Weird socket (see picture of Relay Center, blue flasher module, weird socket to left of it) will be wired for a 30A fuse for the hot side of all of the blower relays. That middle size fuse fits there, jumbo fuses too big.

Since I only have 3 mini relay sockets, have to use on micro and those are hard to find in 12VDC 30A. BTW, if you are looking for a 12VDC 30A micro relay, NAPA has them for over $40, or look for TE Connectivity V23374-A1601-X003 but be careful. It gives a lot of returns but some places don't seem to actually match.

Tried to get a whole wiring harness from switch to resistor pack from Pull-A-Part but I gave up trying to dig around behind the dash, and that harness is taped to another that I didn't have much luck getting loose. So chopped off a couple of feet of the resistor end, as far as I could reach of it anyway. Will be using wire from this for splices up at the switch end to repair that burnt up mess and make more slack up there. Crimped connections with shrink tube and clear shrink tube over that. All this appears to be 12AWG.

Found a blower motor fan switch connector on eBay, new, for pretty cheap. Will be adding that with the correct 12 AWG color wires from the extra harness segment.

Going into the relay box, the input side of the triggers (pin 86) will be the stock 12AWG wires from the switch. The ground (85) will be daisy chained new black 12AWG marine wire to the body or maybe to the 10AWG ground wire. The power for the accessory side (pin 30) will be red 12AWG from fuse and daisy chained across all the relays, with wires from the resistor pack connected to the out legs (pin 87). (whew)

This thing is getting mounted someplace on the passenger side near the resistor pack. One of the screw hole mounting ears was broken off when I found it, so got to figure out a fix for that.

The face of the control was not illuminating since it was "fixed" many years ago. Another thread says that is a 74 bulb, will have one on hand and see if that's the problem. Otherwise will be tracking down what they did to fix that.

Guess if someone wanted to get all super skookum, they could wire this thing up to take the resistor pack plug on one end and have a resistor pack plug coming out the other end or something.

Anyway, got more parts on the way and might have everything by next week.

Or you could do it the awg way hand have it done last month already