Mopar Muscle Association UK

Nope! I am just a colour blind bloke that can read a circuit diagram!

Dont know if this helps cos Im not in the same league as you and Dave, but on the Chally that I owned (71 318), the relay on the right was a delay for ignition light (an option) and delay for the aircon system which was meant to run on for a little bit after ignition was turned off.
My 'key in ignition' relay was plugged into the main fuse box/firewall block near the steering colum. I removed mine as it made a ghastly noice when the door was open, however the car failed the MoT because I hadnt realised the horn wont work with that relay removed!
And, wasnt SteveB right?!

The delay relay for the air con system is just to the right of the resistors for the air con blower motor. The only relay I can see on the diagram with anything like the wire colour codes that Pete supplied is the key-in buzzer which, on the Dart at least, is just under the dash near the glove box.

'Scuse my ignorance here, how does the air con "run on" when the compressor stops with the engine

I know this is a wind up, your an aircon guy right?
According to my Dodge manuals and wiring diagrams (just double checked) for 68 Charger the aircon blower fan (this dosent operate with ignition off) needs to run on for abit when the engine is turned off.
I wont pretend to know why, and both my cars had the air con removed. Also I dont know if this is applicable to a 70 Dodge.
Will try and scan relevent parts of diagrams, and check 71 Challenger manuals.

And I just discovered last night that our Jeep has a headlight delay! If you turn the ignition off before the headlights they stay on for a couple of mins. That had me confused for a moment in the pub car park last night I can tell you.

My Challenger had Air Con same as Petes but it does not have a delay relay for the blower motor.

Yeah I cant say my Dodges fans have run on. Heres a scan of 68 wiring diagran showing AC delay unit. Just checked 71 wiring manual which also has AC delay unit (of different design!) but I cant scan it at mo. Will try again if interested enough! Wonder if delay also might operate the receiver drier switch.
My Rover 820 had that headlamp delay, they said it was so it illuminate your way to the front door. I think it was because Lucas supplied the electrics!

And it was YOUR suggestion that made me wonder if that was what this was so thanks for that. I did think it was just a very good guess though.

But with it being close to the blower motor (and not the ignition) and the wiring (not circuit) diagram only showing an AC delay relay in that area that kind of led me down the wrong path for a bit.

That was why I asked what colour the wires were because then that nailed it down for sure.