Voltage drop, what are the limits?

[ari]

Already posted earlier (79 Spider stalls on electrical load), still looking for voltage drop at positive terminal on coil when everything is on and motor is running. Without a load i'm at about 13 volts, with electric fan, brake lights and turn signals car stalls out at close to 12 volts. Should 1/2 - 3/4 volt drop be acceptable to create a stall? Also, my test light lights up at coil's negative terminal as well, what gives?

[azruss]

your volts are ok. may have a ground issue. are you measuring volts to chassis ground or across the coil.

[majicwrench]

Negative side of coil will show hot with test light if points are open or module is not grounding primary windings.

[ari]

@azruss volts are measured from +ve coil to ground.
@Majicwrench, there's no points, it's electr ignition with module but I lost you after the word not.

[spider2081]

The ignition control module that is mounted in the heat sink for the coil can do odd things. I would change that. Depending on vendor they cost about $20
Are you sure the engine stalls because of loss of spark??
I am not very familiar with the 79 Spider. I would think there are probably one or more electrically operated control valves in the emission system. Maybe one of them is sticky and needs more voltage to operate. If so the car could be stalling because of wrong fuel mixture.

[ari]

Stall is definetely electrical in nature. The coil is interrupted with the electrical load and most likely with the cooling fan being the #1 power burglar. I've already installed a new control module and rebuilt the alternator/voltage regulator.