Changing Lanes with Cruise Control

[Singtoe]

Do you have a trailer hitch? If so, you tail light converter might be bleeding some voltage (bad diode but the flux capacitor might still be good) up past it to the cruise control box.

 

[1st Gen 4Runner]

Does this 4R have aftermarket taillights? If so, there could be a short somewhere. Applying the brake should shut off the CC... but if when turn signal is on and there is a short coming from the turn signal to brake light, this may be a very simple fix.

Again... just a hunch, offering my $.02