Tow Vehicle Charge Circuit Fail
Last weekend, I pulled a float in a Christmas parade, and blew the fuse in my Nissan Titan that gives tail light power to the trailer connector. I was using a 7-pin to 4-pin (flat) adapter, so the only circuits used were tail, and left/right turn/brake. Getting to the fuse was the hard part, but once I did, replacement was easy.
Modern trucks use fuses, links, and relays to supply circuits to the trailer connector. They do that to isolate the vehicle. Remember when adding a trailer would cause turn signals to flash faster?
While checking everything out, I noticed the battery status didn't change much after I disconnected shore power, and plugged in the truck outlet. Verified with a voltmeter, it seems the relay that gives 12V+ to the trailer, to keep the trailer battery charged while driving, had died. I now have one on order. But here's the key point: When did it die? I don't know! The last several trips have been 100 miles away, about a two hour drive. The battery probably discharged some, but got charged back up when I plugged into the campsite and later, when I returned home.
But what if this was a long trip across several states? Where I depended on battery power for overnight stops?
I think I'm going to install a 12 volt voltmeter somewhere, where I can see battery voltage, which should rise when either the converter is on or tow vehicle is connected and running.