I went searching for voltage ratings on crimp terminals, I was surprised what I saw.
Same item rated for 600 volt in US was only rated for 32 volt in Canada.
Most crimp terminal splices like you have were rated for 300 volt or less, sometimes much less!
The thing that scares me is the insulation. 400 VDC is nothing to play with and when an arc starts it doesn't stop until the ionized air gap is large enough.
Me, I would have replaced the whole cable as one piece.
why couldn't you use the original harness from the car, why did you have to splice?