Often the question of grounding arises when a rear light, particularly Service Stop Lamps, on a vehicle seem to be not bright enough.
The original method of grounding was simply a star washer between the Tail Lamp and the Vehicle Body. These washers were an Internal External Star Lock Washer as seen in the photos below.
The Star Washer is placed between the Tail Lamp body and the vehicle mounting bracket to achieve the best grounding, as the teeth of the Star Washer cuts into both the Tail Lamp and the mounting bracket.
Remember the battery ground (or negative) strap is attached to the frame always near the battery location, on a Jeep at the very front. The body is then attached to the frame by bolts and many vibration insulators which are to some extent also electrical insulators so at the back of the vehicle is where a Tail Lamp grounding problem can occur.
Various parts books call up different washers and it is not my intention to get into the social media frenzy about a simple washer but to tell you what works and what we know and have seen on Jeeps and other vehicles over the past 50 years.
The Willys TM-10-1186 calls up Part Number 53024 “Internal – External Lock Washer between the lamp and bracket for ground” for the MBT Trailer.
The same publication calls up 352760 for the same purpose on the MB Jeep but 352760 is an Internal Star Washer.
We should also consider the original paint on these older Military Vehicles was lead based paint, not necessarily a perfect conductor, however modern paints and primers are by comparison far better insulators so restorations using modern paints need all the grounding help they can get.
In summary put an Internal – External Star Washer over each Tail Lamp stud before fitting the Tail Lamp to the body and tighten firmly to achieve a good grounding.
Happy and safe Jeep restoring,