Helix 9 power issue

Are they on the same battery? Is there an inline fuse somewhere?

Seems like a power source issue maybe.

Also, can you swap the power cords? Maybe it’s bad or nicked.

Same source, the multi meter gets the same voltage at the dash and bow, so it can’t be a fuse, there is power there

Bad cord then I would guess.

do you have a 3 amp inline fuse in the units cord as recommended?

If you have stuff networked you may be reading ghost voltage if there is a power or ground problem at that plug,this an issue with sensitive volt meters.
Apply a load like a test light to that circuit,most likely it wont light the bulb now that you have a real load on that circuit.

I assume you tested at the prongs? On the dash power cable try bending the 2 prongs a little. Likely not making contact when plugged in. Helix power cables suck.

If what Joe said doesn’t work, my guess would be what Matt said. You most likely have a bad wire that will show power until you put a load on it. Either the connections at the other end are not making good contact or the actual wire is broken inside! Good Luck!

If you have a friend with a helix take yours unplug his and plug yours in if it doesn’t work call Humminbird tell them and ship back a board might have gone bad . First thing there going to say thou check with a meter how much volts in the plug that goes into the unit. Good luck

Use a 1152 bulb with wires solder on it to test the power, that puts a 1amp load on the power source and that will show a bad ground or phantom power.

You can sometimes still have 12V on a voltage meter, but when you apply a load you don’t have enough amps pushing to the unit to get it to start. Typically it’s a bad, loose, or corroded connection. Assuming your battery is good.

Check the ground. A bad ground will cause all sorts of electrical issues. I had this last night with a minnkota heading sensor. I had 12.5 volts at the source, plugged it in and no dice. Ran the negative to a different ground fired right up .