2003 2500HD won't turn over...any ideas?

[VDZdmax]

I have been having erratic starts out of my 2500HD. Lights come on like normal and when you turn key after glow plugs go out nothing happens:confused:. No bump, no grind, nothing. All the dash lights go out like the batteries are dead, but let up on the key and everything comes back. Try it later, or again and it may start!? I have changed out the neutral safety switch, had a repair shop tell me it was the starter( it wasn't), and now they are stumped. I am wondering about the ignition switch, but don't like swapping parts just to "try" a fix. $$$ Batteries are fine. I thought I had seen a thread on this very problem, but can't seem to locate it. Was hoping someone a little more savvy on the searches could point me in the right direction...
Thanks

[DmaxMaverick]

Welcome aboard!

It could be a number of things. The most common is a poor connection at the batteries, starter or grounds. There's also a starter relay in the underhood fuse box (over the driver side wheel well). The ignition switch is a possibility, just less common.

[Hound]

Have you had your batteries load tested?