2006 F350 6.0 Diesel - Engine lost electrical power while driving. All other power works. When ignition switch turned on dash lights up but glow plug indicator does not go off and engine does not crank at all. Would appreciate quick response (I'm sitting on the side of the road)

. Test all under hood and under dash fuses with a test light or multimeter:

https://www.askmehelpdesk.com/cars-t...tml#post252145

Be very thorough, since it will save a lot of time and money. Don't overlook the possibility of a "mega" fuse on the end of the under hood fuse box.

. Check for codes.

. Check ignition switch for wear, pitting, or melting.

. Remove and fully charge both batteries. Most auto parts stores will test and charge batteries for free. If the batteries are low, it may indicate a problem with the alternator.

. Check battery cables--review ground cable carefully. Clean battery terminals and cable connections.

In a situation like this, you need to start establishing a "known good baseline;" i.e. fuses, codes, battery, ignition switch.

Fuses and ignition switch seem to be OK. Are there any relays that might effect this such as Starter Relay or IDM High Current Relay?

This link may help to troubleshoot the starter motor:

https://www.askmehelpdesk.com/cars-t...tml#post235560

The starter solenoid is the starter relay.

The basic diesel engine troubleshooting link is below:

https://www.askmehelpdesk.com/cars-t...ml#post1415281

With ranchers, in Texas, I've encountered major problems with dirt and corrosion on under hood fuses on PSDs. At times, the problem has been so bad that current would not pass through three or four major circuits. Testing for power through the fuse with a test light or multimeter uncovers the problem. In these cases, I simply remove and clean the fuses with abrasive cloth. All it takes is one important fuse to be a problem.

If starter relay went bad would it kill engine while driving?

No.

I lean towards a problem with the ignition switch, alternator, battery, fuse, or wiring.