The "ground" you stand on

[HingsingM37]

Tuesday I learned yet another valuable lesson from Charles about these old trucks. That having a ground in the circuit does not always mean it is "enough ground". Case in point we have this M37 that is no looker but is getting rewired. It is getting a set of civilian tail lamps mounted under the bed. Upon grinding away some scale and mounting them with star washers I checked for a ground from the lamp to the frame. It appeared good. Testing the wiring we had turn signals and stop lamps but no running lights. I was befuddled as to how this could be? There was power in the tail light circuit.
Charles suggested I buff a spot on the frame and run a separate ground to the frame rail to the lamp body. Bingo, all lights working properly. Those electrical gremlins can be something else

[T. Highway]

David,

Very good advice.

I also learned years ago to use an item made by Thomas & Betts called "KOPR Shield" to help keep corrosion at bay and help with conductivity. I've worked on many snow plow and salt trucks chasing down bad grounds that would drive you crazy.

Bert

[ZGjethro]

I spent a little while chasing down a band ground on a buddies snowmobile trailer. It seemed inconceivable that the metal to metal, bolt to nut connection was not giving a good ground to a tail light. finally I pulled it apart, hit the frame around the hole with a ribbon sander, and presto, lights. It doesn't take much resistance for a 12v circuit not to work

[Cal_Gary]

When I re-installed my front clip I had a dim right headlight, so I took off the front bender brace, ground it shiny where the mount hits the frame and where the top contacts the fender then re-installed the brace-problem solved.
Gary