I don't remember if it was "A" or "B" loop, both loop readings should match.
Hard #3 engine fire loop fault in CFDS. No loop section was identified, only the whole loop system.
First things first, down to the detector unit. Two plugs, each wired the same, one for each loop.
Power, ground, and loop resistance. Power 28VDC - pin"A", Ground - pin"B", Loops - pins "J" and "K".
I found good power and ground. I read the readings below for each loop.
Which one is right? Grab a plug from another engine, 1.4KOhms.
I've got a hard open. I'm reading one (of four) loops which just so happens to have a resistance of 6.8K all by its lonesome.
Pop the cowls. Turn on a flashlight. "It" was found pretty quickly.
Snapped loop, just below insulator. I don't recall seeing one snap in half like this, usually it's a wire harness or a loop faults internally.
ATA 26-11-00 Fire Detection
ASM and AMM 26-11-00