Red cable a Ground??

[Richrsd14]

So, I had to install a new transmission in my 1983 Wauquiez 38, and when the installers were done, the 12V side of my AC/DC panel was dead & there was a loose red cable in the engine compartment near the transmission. So I happened to touch the red cable to an engine mounting bolt for the solenoid & the lights powered up from the panel. The installers had no clue about anything but I actually found a before picture I had taken of the old tranny & it shows that red cable attached to a mounting bolt along with a BLACK ground cable. It SEEMS the red is actually a ground running from the DC panel to the engine block. Does this make any sense? Might the Red cable be an mis-colored DC ground? A red AC ground? I’m attaching the pic. It kind of freaks me out to see a red & black cable connected to the same bolt on the engine! Before I just rehook them up that way, I thought I’d run it by you guys.
Thanks,
Rich
S/V Kayode

[SailingHarmonie]

It makes no sense, but dyi electrics on boats is frequently… to be polite.. a bit sloppy.

Trace the wire see where it goes, make a connection diagram. Hopefully then it makes sense. If it is a ground wire, swap it out for black!

[Bowdrie]

Trace it and the black wire back to the other end.
I've worked on boats where a DC ground wire was a different color other than black, but they usually had a few inches of black tape on them at the terminal ends.

[Avionics_Joe]

Sometimes you make do with what you have in an emergency, but you don't leave it like that!

[wyb2]

Originally Posted by Bowdrie

Trace it and the black wire back to the other end.
I've worked on boats where a DC ground wire was a different color other than black, but they usually had a few inches of black tape on them at the terminal ends.

Replacing it is great, but above is what I would actually do on an 80’s boat that I wasn’t preparing to sell. Tape or heat shrink on the wire, not the terminal, so it’s clear it’s not there for insulation.

[NorthCoastJoe]

The electrons don't care what color the wire is. Common practice is to wrap the last 6 inches of each end in the proper color. So then everyone knows it is ground.

When teaching shop I always stated don't ever go by colors go by where it's connected. I have seen plenty of red negative wires and both + & - of any color on batteries.