General Maintenance & Repairs - dash lights giving a light show

help I just installed a 525HP LS3 in my 2001 WS6 hooked power to it and the dash lights went crazzzzy,I don't know much about electrical stuff so I am stumped any help would be appreciated

Check the battery leads to the alternator and at the fuse box. If they are loose it will cause this.

i had a loose alternator ground in my aurora and it did the exact same thing. speedo and tach jumped like a bouncy ball too.