My friend's car,
About a 2000 ford explorer with a built in plug for a trailer connector. Turn signal and park lights all work right. Wires from trailer connector, LT, RT, and park, show 12 to 14 volts and blink OK...until we hook up the trailer and place a load on them. Then they drop to about one volt or so. The trailer is a small one and is OK, works good on two other vehicles. Vehicle lights keep on working with no change. Found the fuse and it runs trailer and radio amp, and is OK. Radio runs OK when trailer has voltage dropped out. Is there some other fuse, circuit breaker of relay in between power and the trailer connector that is not in the regular tail light circuit?
Kenny