1998 ranger brake lights come on with the key on, led swap

[WHTrunner]

Well it appears that old Uncle Gump was onto something after all.

Just a heads up... if it catches fire... the damage was already done.

Not sure exactly what is on fuse 13... but a safer way to correct your condition would be to put a blocker diode in the brake light circuit going to whatever module is on fuse 13. Probably zero chance of fire.

I think the top suspect for me would be the aftermarket cruise control module. Most all factory modules go through vigorous bench validation from the supplier and internally for these types of things. After production of modules... and vehicles were built they would be validated again... I know because vehicle validation was part of what I did in engineering for several years.

Theres multiple systems that draw power from fuse 13. The brake lights draw power from it, and I believe the abs system is on it as well. I think theres some other systems on it as well. My cruise control monitors it for voltage at either end of the brake switch, otherwise, it draws power from another circuit.

I agree on moving this thread. I havent found anyone with a similar issue and I did a lot of searching.

 

[tony7914]

So I think I pretty well got it figured out. The brake switch itself was not the culprit. Every component that was drawing power from fuse 13 was leaking voltage. So I start with 8 volts on the line, pull the socket for the brake switch, still 8 volts. Pull fuse 13, 2.5 volts. Turn off the switch for my aftermarket cruise control, 0.1v. Just a bunch of stuff leaking voltage. I tapped a tail brake light with a load resistor and dropped it down somewhere where it won't do too much damage if it catches fire, and that seems to have solved the problem. It doesn't even get hot while grounding the leaking voltage.

Interesting! I've got a 97 that's doing something similar after upgrading to LED lights, when you turn the key on not running, the third eye light and the drivers side brake light come on, it's been driving me nuts!
What resistor did you use and where do I buy one?
Thanks!