Not A-body, but....

Be nice if you were a bit more clear. But as mentioned you probably have a ground issue. Every trailer I have had never had a ground wire, they are grounded thru the ball. A bit of corrosion, perhaps with some oil mixed in and you have goofy *** troubles. Run a ground thru the trailer pig tail on your truck. Ad this wire to the pig tail on the trailer. And then make sure that the wires you just added are connected to bare metal. White is ground on most trailer harness's. For some reason most manufactures don't bother hooking it up.