1985 350 HEI dist. replacement

[hatzie]

The moolie that let the magic smoke out of whatever part should never be allowed to touch your truck again.

Supposedly the ESC distributor was only used on the LE9 305. If your truck started life with either of the 350 engines or the LF3 305 it wasn't equipped with ESC. Big Cap ESC is easy to distinguish from a regular Big Cap HEI. With the cap off you'll see two sets of wires exiting on opposite sides of a big cap ESC distributor body. Three wires out one side are attached to the cap, just like a regular big cap HEI, and an extra Weatherpack or Metripack connector (ESC harness) attached to a harness running through the firewall. The ESC engines also have a spark knock sensor screwed into a block water jacket drain plug hole just above the oil pan rail. And last but not least. The ESC ignition module under the rotor has 7 electrical terminals instead of 4.

It's not rocket science to replace the HEI control module. They're nowhere near the cost of a whole reman unit. Usually right around $15 for the AC Delco module. Don't get me started on the Chinese floor sweepings you'll end up with if you buy a brand new distributor.
The HEI module amplifies the magnetic pickup signal to drive a power transistor that switches the coil ground on and off. The distributor body is a heatsink for the transistor... this is why the new module will come with a tube of heatsink grease. Be sure to use it.
The only reason it might fry again is if the harness attaching it to the coil is loose either at the module or at the cap connection.
The original AC Delco modules and coil worked quite well up to some fairly obnoxious RPMs. Unless you intend to drive with the RPMs in the stratosphere for extended lengths of time the stock replacement AC Delco module is the best bang for your buck and the most reliable. The recovery time on the coil was the limiting factor. Modern coils are capable of 7500RPM plus with the stock module. You'll start to see mechanical problems at that speed so the coil is no longer the limiting factor.

As long as the shaft doesn't have a bunch of play side to side and the advance plate isn't flopping around like a wet noodle the distributor you have will work just fine with some inexpensive TLC.

You can replace the advance counterweights, plastic counterweight pivot bushings, and springs if they are too loose. If the distributor needs to be re-curved you'll be replacing them with a new weight and spring set anyway because that's part of how you re-curve the advance. The Vacuum can should be tested to make sure she doesn't leak... If you are keeping it... or just install the new can for your new advance curve.

Hot-Rod Car-Craft HEI Ignition Module Testing
Read this article as well...
Crankshaft Coalition Hot-Rodding_the_HEI_distributor

Rebuilding a big cap HEI