Hey guys, I went to do a yearly inspection on my truck to get it passed for next year, I failed on a few things...

The one that has got me concerned is, my brake lights work when pressed when no parkers on.. As soon as parkers are turned on the brake lights don't brighten, they just stay lit..

When brakes are pressed when headlights are on, the brake lights brighten..


I can't seem to understand whats going on, and I want to try and fix it myself as I have to buy a whole new windscreen, headers/exhaust system, spring shackles and install swivel hub bearings within the next 2 weeks, or else I will have to try to pass an EPA smog test with my old 22R

 

I'll take a guess first that a dual filament bulb is defective. If that all checks out well then I would lead you to a black box-the taillight converter.

Not an expert in any vehicles but particularly an Aussie one.

Do you have a 4 pin connector at the back hitch? Check the operation with an LED tester device. Those boxes just simply fail and cause a variety of odd electrical symptoms

 

Likely a missing or bad ground connection in back. Why? That is a dual filament (1157) bulb, as mentioned above. Wired with two filament connections on the bottom and a common connection on the side of the base. With the parking lights off, the brake light finds ground through the parking light filament and likewise, parking light finds ground through the brake light filament. So in both cases, both filaments would be lit and the brightness is less than normal since you have the two filaments in series and each only getting partial voltage. But turn on the parking lights and now that filament is at 12 volts (instead of ground) and hit the brakes, applying 12 volts to that filament and guess what, no difference in voltage across the bulb and thus no current and no light. I've had issues with the bulb socket ground connection being bad on my VW:
- http://www.4crawler.com/Diesel/Cheap...#SocketRepairs

But could also be a loose or corroded ground wire connection, which I assume is some place near the tail lights.

But yes, could also be a bad bulb (or two), maybe someone put in single filament (1156) bulb or something like that.