Urgent question regarding harness in car

[notarehearsal]

Due to leave for a long journey with one terrier tomorrow morning. I live rurally and won't have time to get to any shops. I can't find terrier's harness. So I have her ordinary collar ( and lead of course) and the seatbelt attachment. Is there a way I can improvise and make a harness so that the poor dog isn't strangled by the seatbelt attachment being attached to her collar? I did google this but was rather confused with the answers

Is she normally well behaved? Once ended up with dog on the gear stick having escaped her collar!

Buy a dog harness? Good luck!

Do you have a dog crate you could pop in boot?

I think you might have to stop at a shop on the way and buy a harness. I would be comfortable using a seat belt attachment onto a collar for a long journey.

I second getting a harness of crate.
If you have to brake sharply you could strangle your dog or even break her neck!

Yes think I need to stop on the way really! Have had such fun and games trying to follow a youtube vid showing how to turn dog lead into a harness! Poor dog thinks she's been just about to go for a walk for the past half and hour!