Solding on a car harness is a bad idea. Should use a good crimp with a joint covered by a dual wall shrink tube that will seal it off from the elements.
I should have updates my how to, I didn’t know better back then.
Solder can crack over time and is not friendly with heat cycling especially when the solder is so close to a heat source.
Would stronly suggest you crimp your ignition wire.
Notice they never have solder on oem harnesses or race cars anywhere, there is a reason for this.