I have a 2005 GT and the right low beam is out, left turn signal not working, brake lights not working and left tail light not working. Cruise control is also not working. I figured it was the passenger side interior smart junction box that was malfunctioning due to a water leak. Water leak fixed and SJB replaced and the problems are still there. Any suggestions on diagnosing this electrical problem. I've had 2 mechanics look at it and cannot figure it out either.
Thanks!
Matt

 

Electrical issues can be time consuming, tedious and a pain to identify. Most mechanics won’t take the time or don’t have the knowledge/patience to trace the problem. It’s not a knock on them but, like home repair people/companies, hvac, plumbing, carpenters, etc all have their specialties.

You should either try an auto-electric shop or try some of your own investigation. Auto electric shops specialize in....anything electrical in cars.

Depending on how bad and how long the sjb leak was present, the wires themselves could’ve become corroded under the plastic sheathing. At that point, simply replacing the sjb won’t fully fix the problems. You can visually inspect them for green crusty stuff (oxidation). You may have to have fix/replace some of the wires.

if the wires check out ok, now you have to do some electrical testing. An auto-electric shop can do that or you can test for yourself if you know the basics of using a volt-ohm meter (VOM).

a very basic, high level over view of what’s involved:

With the fuses left in their respective places, Use a volt/ohm meter to check that the respective fuses for parking lights and brake lights (if different) are getting power (12v). (+) of the meter goes to the fuse metal exposed, (-) of the meter goes to any metal point of the car like a Screw that is screwed into the body of the car (grounded). If you see voltage at the fuses the next thing you’ll want to do is check the power is reaching the rear brake lights.

For that, pull the taillight out and probe the bulb socket. With the power to the bulbs on, have someone press and hold the brake pedal. (+) of meter to the + of the bulb, (-) of the meter to ground (not negative) You should see 12 volts. If you do see 12v, now you need to check for continuity of your ground. The reason you don’t connect to negative is that if the negative (ground) wire is bad, you wouldn’t know so now you’re left thinking your positive wire is bad. By connecting the positive wire directly to ground, you are bypassing the negative wire.

To check for continuity of your negative set your meter to Ohm, doesn’t mater what ohm. Default is 1, open, which means infinite resistance= no continuity. Now, probe the negative wire of the bulb socket with one wire from the meter and ground the other wire from your meter. Doesn’t matter which wire from the meter you use for which connection. If the wire is good, the meter should drop to ‘0’ which means no resistance, the wire is good. If it remains at 1 you most likely have a bad ground wire so the bulb circuit is open.