Thanks guys for the advice.

I'm in Nova Scotia, Canada so it is subject to alot of salt over the winter. I'm gonna have a closer look at the connector and the wiring. I bet something has came apart or there is some serious corrosion.

 

http://cgi.ebay.com/ebaymotors/TRAIL...ltDomainQ5f100


http://www.ontheball.com/taillight_convert.htm


All newer vehicles with 3rd brake light and Dashboard 'bulb out' indicators need a "box" added in line to the normal Tail light harness. It converts the Three brake light system to a two light system for the trailer and it also converts a micro amp directional signal into a strong one for the trailer lights so you Bulb Out indicator on the dash will not turn on from the three to two brakelight conversion.

The Stock harness to your tail lights has a connector on it. When installing a Trailer Harness, you put this 'Box' in line with that harness. Disconnect the stock harness, plug one end into one side of this box then the other end into the other side of the box. Many SUV's has this harness on the drivers side where the Jack is. not sure about Blazer.
Even though this box is basically used to convert a three brakelight harness to a two light for the trailer, the Running lights also runs through this box. When my brothers went bad, he had many weird things happening. Not just Brake light issues.

 

It had worked fine for years without a "box" installed so I don't think that is the problem. Probably just something loose or corroded with the harness or wires, at least I hope it is.

 

Are you sure when you had the Harness and hitch done for you that they didn't add this?

 

sorry, not on these Blazer's. i had to run every wire for the 7 pin on my hook up, and havn't had any problems with it. also did the hitch & wiring install on one of my brother's '02 Astro, no plug-in from the factory on it either, and no issues with that one either.

let us know what you find in there Zyan.

 

I am working a friends trailor. He had no lights working. Got the blinkers working and that was all. I crossed a ground and blew my tester and got another today. Now no lights are working. I am guessing I blew a fuse under the hood. I didn't even think about that until I was reading here. Are these fuses covered? The reason I ask is that I don't want to have to go buy all the trailor fuses if not needed. So do I need to test them or is there a way to look and tell if one is blown. 2000 TrailblazerLT 5.3 4wd. To my knowledge there is no fuses between harness connector and harness like my old 87 ford truck had.

Thanks in advance.
Jerry

 

I have a little loopback plug that i plug into my vehicle harness and it has lights on it that gives you a visual reference to tell if your wiring is good on the vehicle. They only cost a few bucks but good for troubleshooting. With that you'll be able to isolate it to the vehicle or the trailer side. good luck!

 

Well all trailor fuses under the hood blew when I crossed that ground. DoH on my part. Replaced and all is working now.