I have used a Megger on engine loops, but I'm not a fan of using one.

A Systron loop is pressure filled, so a Megger shouldn't hurt it. The Kidde???? I would stay away from a Megger.

With this problem, after we used the decade box for substitution, the loop read 30MΩ (that was just from removing the one terminal lug).

We smacked the white doughnut pretty hard and the 4.5KΩ returned. It didn't fail after the beating.

I use a regular VOM on most engines loops. A LCR Meter can also be used.

A LCR Meter should "always" be used on body and wing overheat loops.
  
     
 

Mark did you try to test the loop with a megger once removed? I remember it being a way to find intermittent loop failures but blurb in the manual that the loop must be clean prior to using the megger.

767 with a hard fail on the left engine EEC (Electronic Engine Control).

Engines with a EEC have a mechanical fuel control. FADEC (Full Authority Digital Control) engines have a HMU (Hydromechanical Unit) to control fuel.

Either way, the EEC or FADEC require external inputs to assure proper engine functions.
  
     

With this problem, the EEC's were swapped between engines. The problem didn't follow.

We put a meter to all external inputs and measured the torque coils and feedback wires to the fuel control.

We found the T1.2 temperature sensor reading open. We verified the wires to the sensor plug were good. Resistance readings directly at the probe still had the open.

After a replacement sensor was obtained, we checked resistance. It read 220Ω.
  
     
  
After the replacement and engine run..... all EEC functions checked normal.
  
     

Interesting problem today. The right engine loop 1 was showing as failed on EICAS. The system installed was a Systron-Donner.

We disconnected the pylon plug and checked the total loop resistance 1.5KΩ, this is a good reading.

Moving to the...

After a Auto-Throttle clutch pack replacement in the nose compartment, we had a "Left FCC A/P Disconnect Switch" fault during MCDP (return to service tests).

This doesn't mean the left switch is the bad one because either switch could be the issue. The right and center FCC's can throw the same message.
  
  
     

The FCC's want to see a ground on pin "F15" of the "B" plug during system tests. Unless either yoke disconnect switch is depressed, the ground should always be present.

The signal path goes through the F/O's yoke, then the Capt's yoke in series.
  
     
  
We were open to ground from the Left FCC rack. I put a tone on the wire with the "Fox and Hound".
  
     
  
I had good tone under the F/O's yoke, but it died when making my way over the the Capt's yoke terminal block.
  
     
  
Backtracking to the area above the clutch pack we found this shit.....
  
     
  
One broken wire (ours) and another jewel of a wiring repair right along with it.

Regular butt splices hooked up to bastardized environmental splices on two sets of wires with about 8 inches between each of the splices on each wire. The environmental splices didn't have the sleeve shrunk down and a crimp on one of the barrels done with flat faced Knipex pliers.

We repaired the wires properly but seriously..... WTF??