Motorhome marker lights

2000 motorhome parking/clearance light issue. Recently purchased a 2000 motorhome (third owner) sitting on a Spartan diesel pusher chassis. Day one noticed the parking/marker lights did not turn off with the 90s Ford Ranger style dash pull switch sometimes, after a couple on/off with the knob they would go off. Checked and the relay for that circuit was warm... all the time. Assumed it was a switch problem, so pulled the knob turning on the light so it would release with the button, unplugged the switch... the lights stayed on without a switch. Pulled the relay and they went out. Checked for current feeding the relay next. in the block #85 was hot w/ 12v all the time, #86 was a ground, #30 was dead, # 87 was dead. Plugged in the dash switch, turned on the parking lights... they came on with the relay unplugged...??? Tested the circuits #85 was still 12v, #86 was ground, #87 was 12v, #30 was 12v. ??? This motorhome has a DOT switch to flash the marker lights, so I unplugged it.... no difference at the relay block or light function. As I understand 12v auto wiring.... 85 and 86 control the coil with a feed from the switch, either 30 or 87 should be 12v all the time to complete the circuit once the switch is activated by 85/86. This unit has 16 incad marker lights plus the 4 tailights and 2 parking lights... no way they would run that much draw thru Ford Ranger headlight switch. I am thinking there is a problem between the switch and the relay block that is powering 85 hot all the time, but that does not explain why 30 or 87 are not hot with 12v .. any thoughts???Fix one thing, and mess up 2 unrelated items in the process.

if 85 is hot and 86 is ground WITHOUT the switch then something is activating the relay that shouldnt be. the only thing you can do is trace the wire. I would start at the plug for the switch and just make sure its not damaged no frayed wires etc. the trace the wire back to the relay. somewhere along the way someone has tapped in to the wire for something or the wire is shorting to a hot wire of another circuit. if you have trouble tracing the wire you may be able to narrow down what circuit me be shorting or tapped in to it by pulling fuses one at a time and also activating and deactivating ALL 12v house/chassis switches. lights, water pump etc.Gary Sather

The main wiring harness from the dash area is the size of your arm, and the 2 other from the leveling jacks and other items in the front are larger than golf balls. Snaking around they are almost impossible to trace as they pass behind stationary panels and thru a bulkhead connector block, to another short harness, then thru another connector block into a box in front of the front wheel well. Have cleaned all the bulkhead connectors and applied dielectric grease, and traced the wires as best as I can... even had one of my old drivability techs that is a real pro on auto wiring harnesses spend an afternoon... he could find nothing. I have found if I leave the relay out.... the lights work fine thru the switch... and for now may leave it that way since I seldom drive at night.Fix one thing, and mess up 2 unrelated items in the process.

A power probe ext2000 is helpful for this. Helps trace shorts through large bundles and firewalls etc. Power probe Gary Sather