1980 300 6. Any idea what these wires are for? Two pigtails next to the brake booster and one in front of the ignition box?

 

I'm interested in what these are used for also. My 1981 300 has the exact same setup without an attachment in the area that I could find.

(I always assumed it was for features added to the higher end models but they used the same wiring harness??)

 

I believe the larger yellow wire is for an optional trailer towing package and perhaps the other one [if always hot] is for the optional under hood light.

 

That makes sense. I'll have to check the voltage. The yellow and grey one up above almost look like they were meant to be plugged in together.

 

Light green/yellow-stripe = always-on, fused accessory feed for the underhood lamp as David said.

The other one, hard to see your picture but if it's a thick, yellow wire (maybe with a blue plug) then yes, that was supplied with trailer towing/camper packages.