Not cranking

[dpain]

Hello
I'm new and need help.
I have a 2002 Duramax diesel/manual trans with 160,000 mi. Never any starting problems and has 2 good batteries. It will not crank from the key. You can crank and start/drive by shorting the solenoid to the starter and it runs fine. Or pop start on a hill. Turn the key and all lights light up turn the key to start and lights dim a bit no solenoid click. I have put in a new starter with no change. Any ideas

[rapidoxidationman]

My 6.5 had a starter circuit relay in the engine compartment fuse box. Not sure if the 6.6 does too, but maybe you've just got a bad relay?

[DmaxMaverick]

Welcome aboard!

Yes, there is a relay in the underhood fusebox for the starter. There are a few of the same relays, so swapping it with a known good relay should help with your diagnosis. The relay locations are marked on the fusebox lid.

[dpain]

I swapped 2 relays. Still no crank.

[DmaxMaverick]

That doesn't leave much. Check the clutch switch for correct operation (opens/closes with clutch use).

Then....

With a helper, turn the key to start, and check the relay for a click. If it doesn't click, suspect the ignition switch, or an open connection (poor or loose contact with a connector, or broken wire). If it does click, chase the harness back from the solenoid/start wire at the starter.

[dpain]

Now the trans is out and the starter fix is on the back burner.

[More Power]

Yes, it sounds like a clutch interlock switch... Jim

[dpain]

OOO yeahhh.
Sure is sweet when it goes together and works better than expected.
After 160,000 mi of progressive deterioration the clutch finally went out but for the last 40k the clutch has been marginal and shifting difficult. The flywheel was out of balance and the t/o bearing on the verge of failure so it made a racket in neutral and ran rough. Things still worked so why pull the trans. When the t/o bearing finally blew up I had no choice.
I replaced the clutch master cylinder and hydraulic hose. The dual mass flywheel, clutch and slave cylinder with throw out bearing and an oil change for the 6-speed.
The test drive was amazing.
The clutch engaged smoothly with no vibration. The new flywheel spun like it was supposed to with no low speed vibration. The transmission is so smooth I can shift easily.
Which brings me back to the purpose of this post. NO CRANK.
I could not crank the engine from the key switch. The new clutch master cylinder comes with a new interlock switch. When everything was replaced I ended up fixing the original problem that started almost 3 months ago.
After years of working on vehicles this is the best.
Thanks for all the suggestions along the way.
David