If the car is totally dead (headlights will not come on at all), then the problem lies between the batttery and the in-harness splice.
Start by looking at:
1) the battery connections and the connections on the large lug on the starter relay
2) then the fusible link (can blow open and may be a sign that there is a developing short, which may be causing the 'headlights kill ignition' problem)
3) then move on to examine the firewall connector where the fusible link and its wire go through
4) then the ammeter and its connections
5) and then the harness splice in the dash.
BTW, why did you tow your little brother? Wouldn't it make more sense to tow the car? LOL...sorry...could not resist...