Christian, First question are you changing from points distributor to a HEI Type distributor,if so then you have relief coming,i.e....Look under the dash to the fuse block,put your glasses on and bright small flashlight..You will be looking for a place labeled IGN fused or unfused that will have two flat pins you can slide on a spade with #12 -14 gauge wire (preferably red) and find a hole to run this wire through the firewall,which should be long enough to reach the HEI distributor ('75-"80 OEM Chevy dist.) and install a spade on the end and slide it onto the + side of the HEI dist. and also your TACH.
There is NO power at the IGN spades until you turn key to run/start position.
Now if you stay with the points system then you have what you have,however YELLOW wire is to the R on solenoid,terminal close to the exhaust and the PURPLE wire to S terminal closest to the block( GM did not want it to easy for you to connect this wire ... Have fun and a Great day.....Sal C nosal1