Runs 15 minutes then dies and won't start

[davids2toys]

Originally Posted by rnkjr

Chat GPT: Most Probable Causes (ranked)
1. MSD 6AL box failing when hot
Why this fits perfectly:

Car runs normally until fully heat-soaked (15–20 minutes).

Engine dies instantly, as if key was turned off — classic MSD box shutdown symptom.

After cooling 20–45 minutes it restarts immediately.

Numerous coils tried → no change.

Pickup tests OK cold and hot.

Grounds check OK.

Ignition switch replaced with no improvement.

Important detail:

MSD boxes often fail only when hot, and about 70% of the time they still pass the "paper clip test" when tested immediately after failure, especially if they are in the shade or starting to cool.

Even when they pass the paper clip test, the internal capacitors or the switching transistor can break down under heat + load.

2. Magnetic pickup intermittent when hot (despite 674 Ω)

Even though resistance is correct (MSD wants 500–700 Ω), failing pickups often:

test perfect cold,

test perfect immediately after a shutdown,

but fail only under thermal expansion + vibration.

This can produce the “dies instantly at a stop sign” symptom.

Testing tip:
Check AC voltage output while cranking during a hot no-start. You should see 0.3–1.0 volts AC.
If it drops to 0–0.1, the pickup is dying even if resistance is normal.

3. Heat-soak failure of the coil trigger signal path

You already tried multiple coils — that strongly suggests the coil is not the problem, but the trigger path TO the coil might be intermittent.

This includes:

MSD box to coil wire (heavy red + heavy orange)

MSD box ground path

Small red wire (switched 12V) heat drop / intermittent open

Loose spade connectors at the box

A small-red-wire voltage drop is a known MSD shutdown cause.

Well the first part of this certainly sounds like my issue. The pickup was put in a few years ago but has had hardly any use. Also looks perfect. When I called MSD the assured me if it passed the paper clip test it is DEFINATELY not the box!
So how do I do this AC voltage test? Where am I doing this test? What is the voltage drop/ heat drop at the small red wire, I don't understand. So what am I looking for at all the other locations you listed. I only have one spade terminal (yellow wire), it is on tightly