Instrument cluster panel problem on 82 MB 300D Turbo

We recently had a shop replace our ignition switch and the backup light switch somewhere on the rear end. We got the car back and as soon as we went down the road and turned on the turn signals, wipers,
or headlights the whole dash went crazy. The fuel gauge jumped up, and the seat belt buzzer kept buzzing.
We took it back, he said he'd fix it for free (because he screwed it up) and stuck another used panel in. Then on our way home it did the same thing. We called him and he said bring it back. We told him we couldn't get there for three weeks due to business (and he's 62 miles from our rural home), and the owner said that was fine.
WELL, three weeks later we go in and he looks it up on his computer and says he has no record of an instrument panel repair. We reminded him of the "freebee" and he innocently explains that he cannot warranty "something I did for no charge."
Cute, huh?
Does anybody have any idea what may be the problem so I can attempt to repair it myself ?I had a similar problem with an old BMW 2002 years back, but can't recall how I fixed it.
Thanks
Jim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sounds like a bad ground. Check the multipin connector on the back of the dash (maybe he let it fall apart and the wires were not reinstalled correctly). Bill Ditmire Ditmire Motorworks,Inc. 425 White Horse Pike Absecon,NJ 08201 http://www.ditmire.com 609-641-3392
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.