For automatic transmissions, it's generally found on the side of the transmission case, near where the shift linkage connects. It's often a small switch with a single or two electrical connectors.
For manual transmissions, there is no neutral safety switch. The starter relies on the clutch pedal being fully depressed to prevent starting the truck in gear.
To be certain, you should:
1. Consult your owner's manual: This is the best source for your specific model.
2. Look at a wiring diagram: A wiring diagram for your truck's year, make, and model will show the location of the switch and its connections. You can often find these online (sometimes for a fee).
3. Use a Haynes or Chilton repair manual: These manuals typically include diagrams and instructions for locating and replacing the switch.
4. Search online forums: Searching for "1988 Dodge truck neutral safety switch location [transmission type]" on forums like DodgeTruck.org may yield helpful photos or descriptions from other owners.
Caution: Working on your vehicle's electrical system can be dangerous. If you are not comfortable working on your truck yourself, take it to a qualified mechanic.