Trolling motor wiring help

[Dramad1]

I took my kayak (nucanoe unlimited)out to.el cap today, its been a few months since taking it out. Day was slow but managed 3 dinks by the end of the day.
Day was going fine, hit all the usual places, decided I was going to explore the far back as I never travel that far nor have I seen many people go back back to the back. Turned the bend and started heading back, cranked the trolling motor up to full power (motorguide xi3).
10-15mins of travel i was about half way back. I started smelling a burning smell, I looked back and seen the negative side on my pig tail to the 12v 100amph battery smoking. I quickly cut the power and Inspected the wiring. Negative side plastic sheathing was melting, wire was hot. The positive side was normal and cool.
The motorguide xi3 connects to a marinco plug in the front of kayak, 6g marine grade wire runs through the boat to another marinco plug in the rear. About 12' of wire. The marinco plug in the rear is connected via pig tail (16")with 6g wire to a newport vessels battery box with built in fuse. The fuse is inline with the positive wire(red), it did not pop.
After I cut the power to the motor, I drifted for 15-20 mins. I inspected the terminals and wires at that time and let everything cool down. I pulled up the trolling motor and rudder and began to paddle. 10-15mins in, I maybe move 50-80', it was a losing battle with the wind and current and such a heavy kayak.
I decided I needed help and chanced the trolling motor, battery looked fine and was cool to.touch, power cable now cooled, I started the motor on its lowest speed setting and began paddling. Constantly checking the wiring on the pig tail. All seemed fine. Decided I wasn't moving fast enough and increase speed a bit more and continued to paddle and monitor pig tail, motor and wiring.
This continued for 30 more minutes, eventually getting the motor up to half speed. At this point I just wanted to get off the water before I got stuck out there trying to paddle my butt in from the far back. It was a mission but I managed my way back to the launch.
Loaded up and inspected wires, just the negative side on the pig tail. Motor fine, battery fine, fuse still intact, marinco terminals look normal. Headed home and decided on the way that I may need to rewire my kayak with maybe 4g wire?
Could running the trolling motor at full speed for 15mins straight cause excessive draw on the battery? I've never had issues before, I've been to most lakes around San Diego county front to back full speed, put a pretty hard load on the motor and battery. Never ran the battery empty yet, motor has never had any issues other than dead battery in the remote and try to maintain motor after each trip, clean, remove prop, remove any build up, oil the release bars etc.
Im still pretty new to being off the bank in my kayak, never had a boat let alone a trolling motor. This kayak and motor/battery has had about 80 trips out. I feel the trolling motor itself is not enough to power the kayak and or not intended to pull the kayak around like a actual motor. I have been thinking of adding a nk300 to the rear for traveling and use the trolling motor as a.trolling motor spot lock once at fishing location. Still undecided as the added weight, additional battery etc.
Long post, my apologies. I guess I'm looking for help, suggestions, thoughts and what could have caused this, recommendations. Should I rewire the kayak. Do I need a different battery, is this normal when under heavy load.
I'd really appreciate any help, ideas though, thanks everyone in advance.

[Bendo]

Nobody chimed in, I’m surprised. First thing I thought was you may of had some corrosion on the Negative Terminal or it wasn’t tight enough. Assuming you had 6g Wire coming off the Positive and it wasn’t Hot, there had to be some resistance to the Electricity returning to your Battery at the Negative Terminal. The other problem if all was good, is the Battery is wearing down and couldn’t handle full speed.i was told when I bought my 36 Volt set up to never run it all the way full and it would last a lot longer. So I never have. Hope this isn’t too late. Please let us know what you found out.

[Dramad1]

You nailed it, slight corrosion on negative terminal and loose wing nut at battery.
After some research and inspection, quick shout out to chatgpt, I've decided to rewire the kayak with a higher quality marine grade 6awg copper tinned wire. Chatgpt helped me source the internet w/ similar issues and gave me manufacturers specs on motor, fuse, wire, battery, length of wire etc. It was extremely helpful.
The wire actually just arrived today. After doing a side by side comparison (new wire vs current wire), the new wire looks to be a true 6awg size wire w/ proper insulated sheathing where my current wire looks closer to an 8g awg wire with thicker soft sheathing.
I've rewired the pig tail today, new hex crimped terminal connections, sleeve connectors at marinco plug. Plan to rerun wires through the kayak tomorrow, it was still a bit to wet out there today.
Thank you for replying, definitely appreciate it. For me its been a lesson full of useful knowledge from the experience and the trouble shooting.

[Gotfish?]

Also, not a bad idea to glop the connections with dielectric grease, especially if they could get exposed to salt water spray. Scuffing up the battery terminals and wire terminals with a wire brush gives a better connection. Getting a good, tight crimp is critical too. I personally prefer solder over crimp, especially if the crimp connector is nickel plated.

But most likely, your problem was solely due to the loose wing nut. If the problem was due to the wire, the positive side wire would have been hot too since it carries the same current as the negative.

[Bendo]

My experience came from running a full Electric Powered Bass Boat on Mission Viejo Lake. A 36 Volt Motor on the back with three 12 volt batteries in series, 1 deep cycle 12 volt battery running a 48x18 inch livewell under the middle seat plus the fuse box to the lights and radio. Then a 16 Volt deep cycle running the FF. Quite the wiring with 3 battery chargers. I chased World Record class Bass. I’ll never forget putting the net under a 16 pound Bass for my Dad. His eyes never got wider than that moment, then two years later, getting an 18.4 to beat his fish. Man I thought that was the 22 pound Bass I had fished for all that time. She was a true giant. Sadly, the Lake was afflicted with Golden Algae and every fish in the Lake died and nothing lives there to this day. What a special place that was.

[Dramad1]

Just finished running new wire.through the hull. Everything went smooth. Used the old wire to pull the new wire through. Noticed a bit of condensation built up from all the hot/cold days. Wiped.up what i could and then ran a leaf blower through the hull to dry things out completely.
Used new farills sleeves for marinco connections. Looks nice and new again. Noted on the die electric grease, gotta go grab some.
The new wire is so much more stiffer that what I had in there. You can definitely feel the difference in quality.
Thanks for the advise, tips and help, it is greatly appreciated.
Those bass are giant! Very nice

[Bendo]

Now, go get some Fish!