As a registered professional electical engineer with over 35 years industrial experience, I can assure you that the best approach to electrical connections that are designed and built correctly is to keep them clean, tight and dry! "Keep" implies a regular check of connections to clean, tighten, and dry them. When you do this properly, dielectric lube, axle grease, vaseline, et. al. is unnecessary. Leave it off - just MHO.
Earl and Bettye
2011 Cedar Creek Custom 36RE
2008 Ford F-350 CC Lariat 6.4L Diesel DRW 4x4