Toyota pickup's weird electrical problem

The parking lights on my 96 Toyota T100 pickup (4cyl.,132K.)come on by themselves when truck is parked. The light switch is in off position- and turning it on/off will not turn lights off. If we are aware of it happening I disconnect battery to prevent total battery drain. When battery is reconnected sometime later (perhaps days later- we use truck only occaisionally) the lights are back in the off position. This happens about once a month or so- more frequently recently.(it happened once during a rain storm & other times in dry weather) This other problem may not be related but the ignition switch when turned on does nothing for several tries and then will start - maybe a bad ig. switch? Thanks.

Looking at some service data it shows that the lights are controlled through a taillight relay and a switched ground through the light switch. The switch may have an internal short so I would first see if disconnecting the light switch clears the trouble. If not, then it would seem there may be a intermittent short to ground on the wire to the relay coil. It is a red/blk wire. You could verify that by checking the voltage on the lead. There should be 12 volts on the lead while the lights are supposed to be off. The lead will have no voltage on it if there is a problem on that lead and the lights are on.

Sorry it took so long to reply- had the death-flu. Thanks for the help. It did it again yesterday. Came home from work & the truck(parked in my driveway) had park lights on. Tapped and jiggled switch but lights stayed on. Disconnected and reconnected pos. battery terminal and lights went off and did not come back on! Could this mean its relay and where do I locate that. Thankyou.

You’re welcome for the help.

The relay may be the cause of the trouble or there may be something wrong with the control lead to it. Perhaps something is backfeeding to the control line. Proper testing would tell the story on that. The relay may be located in the power panels under the hood or possibly the dash. If you are going to work on this yourself I highly recommend you at least get a factory service manual for the wiring. The investment in a manual can save you a lot of time and money and can pay for itself with the first job you use it on.

The problem with the ignition switch may be related to the light trouble. I would first verify that power is getting to the ignition switch. You need to see if the switch is the trouble or the wiring to it. If you don’t have a test light probe or voltmeter to check for voltage you should add that to the list of items to get.