I've checked the DC distribution panel, those fuses are all good. Switched grounds are a pain!
Old detector was a CCI Controls 7719. I have removed that valve when trying to get gas to the stove. New detector is a Pangaea PRG1000A.
The old detector had a yellow and 2 reds coming out of it.
Those were spliced yel to yel, red to red and red to gray going into the floor.
The red and gray may have touched. I didn't see a spark but may have missed it.
Red to gray measures 0.5v
Yes to red and yel to gray measure about 40mv.
To finish tracing the red/gray wires through the underside and forward I will need jack up the driver front tire and then maybe remove the wheel for better access, but I bet it disappears into wrapped bundle.
Thanks!