I'm currently having trouble diagnosing a brake light issue. Neither of my brake lights are working. I was having an issue with the left rear turn signal. The turn signal would blink fast indicating an issue and occasionally blink at the normal speed. Now the turn signal has switched and is blinking normally, with the occasional fast blink. The bulbs were good, so I'm not sure of the issue there. I also have noticed the cruise control is not working which I believe is tied to the brake light issue. I have checked the fuses and I cannot get the 15 amp VEH STOP to get my automotive circuit tester to light up/make sound. I pulled the fuse and checked continuity on my multi-meter and it showed continuity, so it does not appear to be a fuse problem. I ordered a driver side tail harness (needed this regardless because of some shoddy rear camera install work on my part, trying to correct the shoddiness). Received the wrong one and will have to wait a few days to get the new one via Amazon. Regardless, I don't believe this is the issue, but was wanting some more expertise than I have. Any help would be appreciated on where to start.

My truck is a 2005 Suburban 1500 LT, 4x4, with power adjustable pedals. I know there are different brake light switches for adjustable/non-adjustable brake light switches so thought I would include this detail.

 

the instrument panel fuse box 15amp vehicle stop fuse is powered from the underhood electrical center stop lamp fuse 25 amp. check the 25 amp fuse; it should be powered at all times.

 

I just checked the 25 amp fuse and it was good.

 

pull both fuses...find the pin that is not powered at the hood fuse box....check for open with an ohmmeter to the pin in the ip fuse box. if its open...the problem is either an open wire or bad connection in the under hood fuse box....from the fuse to the connector underneath.

remove the connector in the underhood fuse box and recheck the wiring with an ohmmeter...if its ok...the fuse box is the problem.

 

Tech2, first of all I wanted to thank you for your help. I did the above and my ohmmeter does show the circuit being open. When I press the brake pedal, the circuit closes and I get continuity at that point. I'm assuming this is how the circuit should operate to power the brake lights at the application of the brake pedal.

 

Tech2, I found the schematic and I think I need to check from the ip veh stop fuse to the rear junction block. Does this sound right? Also, since the second step you recommended sounds like it was ok, does that mean the brake light switch is good?

 

post the diagram you have.
you don't have power to the ip fuse...that is what you must figure out. everything after the fuse is irrelevant at this point.

 

Here is a link to the diagram. It is the very last diagram in the bunch.

https://www.autozone.com/repairguide...96b43f80cb1cbf

The underhood fuse box shows open to the ip fuse box until brake is pressed. I removed the rear junction block and cleaned the wire harness plugs. Lots of dirt. I checked the continuity of the junction block to the corresponding tabs. Everything looked good. I plugged everything back in to the block. Prior to cleaning the block, I didn't have voltage to the brake light portion of the harness at the light lens itself. After cleaning it, they worked! I'm a relative newbie to auto repair, but I'm an electrician, so I was hoping I could figure it out with a little help. Once I checked what you said and found the schematic, it seemed to fall into place. I was worried I wasn't going to get voltage from the ip fuse panel and the junction block and would then have to replace that whole wiring harness, which may have been a little above my auto repair knowledge. Thank you so much, Tech2. I wouldn't have been able to fix this without your guidance.

 

the diagram I had didn't show the brake switch between the 2 fuses. good find and fix