what gauge of wires?

I crimped the wires as hard as I could but useing parts house taiwan blue & yellow connectors which are cheap/poor quality. Today I went to solder them in addition to the crimping but my very small soldering iron could not get hot enough. I can get a larger iron or am I go to go as is?
Maybe but it won't guarentee a better connection. That's the weak link and my only guess as to why so many use them is its like a bowl of chips on the table in front of us. Its so easy to just grab a handful rather than, or in addition to getting that corned beef sandwich or BLT in the kitchen.
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Can be OK for a quick repair or in a non-critical location or with good wire support.

One problem is we just can't see the crimp.
Another problem is the wire insulation isn't connected.
This creates a stress point in the conductions just behind the crimp.
Adding solder may help the strength of the connection but moves the stress point further from whaterver support it got from the terminal.

You can buy terminals made for soldering. Support the wire so there is good stress relief and use heat shink. Some of the marine terminals shrink their insulation onto the wire.

Ever see those cheap terminals on a new car? a new boat? a new airplane?
There's a reason for that!
The Packard type terminals haven't been the standard even for automotive use in quite a while, but they are far better, when properly made, than the blind squeezed terminals. I'd consider an double winged open barrel terminal as the baseline. Getting stranded or starting a fire in the middle of a roundy round track can't be any less dangerous than loosing power out on the water.

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https://www.forabodiesonly.com/mopa...er-type-wire-terminals.418908/post-1973773745
https://www.forabodiesonly.com/mopar/threads/electrical-solderless-or-soldered-connectors.541024/
I cringe with every other post in the electrical section where someone has "improved" or "upgraded" their system and used garbage terminal connections. All is fine until current tries to flow through these porly made, or highly stressed high resistance connections. Only takes one bad one to mess things up.