The answer supplied by SnoKing was VB related, but there were steps in that post to troubleshoot electrical vs VB issues in that post if you step thru that whole post again.
If you decide on a Mystery Switch IMO, if you jump over to mopar1973man.com you can sign up for a monthly membership for a few bucks, there are articles on how to build a mystery switch to control lock up. It's on here as well somewhere, their format is a little bit easier to find the "article" it's not a post.
You need to figure out if it's electrical or mechanical and go from there.
I have see posts about bad internal harnesses, so when I did mine it was recommended to swap the harness with the new parts, you should be able to check the harness.
Don't have a shop per say.. but if I was looking here is how I would find a shop...
Goerend is a very good supplier, they do not do builds anymore, but their installer list should be pretty solid shops, but I don't know about where these places are, it's a starting point if you need a shop.
https://goerend.com/installers/
Find one near you and see the reviews of those shops, you can also call Goerend and see if they are still a recommended installer in case there was an issue and they were removed but web site not updated.