Back in the 90s I  used to install  kits from Rostra and Audiovox, not sure how old your truck is but if you k ow the dealer that sold it they will probably  know who installed it. other options  are call or email Rostra and Audiovox
ETA
I did more research, I can't  post links but if you look  up "The cruise control store" they have an 800 343 1382 they should be able to help