I have a '95 GMC Suburban. It blew the 30 amp ignition control fuse. I swapped a 40 amp spare I had w/ same result. No idiot light in the instrument cluster show up until a new fuse is inserted. There was no warning of any pending trouble. It ran great. It has a new starter, alt, battery installed within 1 year. Tow ruck operator suggested wiring problems in steering column. Sounds pretty complicated. What troubleshooting can I do.

You put in a 40 amp fuse blew?
Idiot light lit up, and then blows?
When does fuse blow? When you turn on ignition? Idiot light lites and then blows?
Replace with 30 Amp.
Maybe remove fuses to ignition controlled items(smaller fuses)
Then add 1 by 1, until fuse blows.

I have a '95 GMC Suburban. It blew the 30 amp ignition control fuse. I swapped a 40 amp spare I had w/ same result. No idiot light in the instrument cluster show up until a new fuse is inserted. There was no warning of any pending trouble. It ran great. it has a new starter, alt, battery installed within 1 year. Tow ruck operator suggested wiring problems in steering column. Sounds pretty complicated. What troubleshooting can I do.
Change out the larger 40 amp fuse with a 30 amp circuit breaker, it will reset itself automatically. Give more details on exactly when you lose power. Is it right away or 10, 20,30 minutes later, or while turning the steering wheel, or doing some other function?

I will help all I can.
Arty

First, disconnect the negative battery cable and check out the starter motor. The armature winding may be shorting out. Second, remove and check out the ignition switch. Here's what it looks like:

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As I'm sure you know, it can cause big trouble substituting a larger fuse.