Car died during driving

I have done my share of circuit chasing,this would be an easy one. For example,if the heater is one that quits with everything else then turn on key,turn on heater and carefully start wiggling and pulling wires. This is the most effective way to trace a fault. If heater isnt affected then may need to use the lights and watch carefully. The basic circuit depicted above totals about 30 feet of wire unlike the vehicles of today with hundreds of feet of fragile wire and 18 computer modules. Looking for electrical trouble in a 70's car is a treat for me.

Unlike today, pulling heads off a ford 5.4. Gonna be a bad day.