The first question I have is it possible to get an electrical schematic for my 2004 silverado Duramax? At least the section pertaining to the CHMSL circuit. My research shows the CHMSL circuit runs the third brake light at the top of the cab and provides 12V to the trailer brakes at the bumper 7 pin connector. sporadically I blow the CHMSL 10A fuse and lose automatic function of my prodigy brake controller. The manual function still works the trailer brakes. I have proven that it is not the prodigy brake controller by removing it along with the factory pig tail that plugs in under the dash. When everything is disconnected I replace the 10A fuse and tap the brake pedal and POP! The fuse blows. I have removed all the lights and verified the wiring is not shorted out at the top of the cab and the third brake light. Then sometime in the future I can replace the fuse and all is OK. Plug in my fifth wheel and take a trip and all is OK. Unplug the trailer. Go on a day trip. Come back and hook up the trailer, touch the brake and somtimes it's fine sometimes it blows the CHMSL fuse. Remove everything I can think of and the fuse still blows. It's as if something like a relay is latched up and whatever it is latched up to , blowing the fuse. The relay or whatever relaxes and all is good for awhile. If I had a schematic I could break the circuit and isolate it to a section. Right now I'm on the road and can only control the trailer manually. Works but not the safest situation I can be in. I did put in a 15A fuse once and blew that. When the circuit is working fine I have put in a 3A fuse and not blown it. (Not with the trailer hooked up) Any ideas? I'm stumped.
Workerb
I would look at the plugs at the rear of the truck where all the lights connect, check for corrossion or bent pins. I would aso do this to the plug under the dash.The only way I know to get a wiring diagram is through the GM website, unless you can find someone with a gm repair manual.Hope this helps
Page D-155 here (select page 251) http://www.gmupfitter.com/publicat/2004_BB/2003_Beyond_LD_Electric_CK.pdf
And check to see if the Light Blue wire with a single, capped off plug, by the 7 pin trailer plug isn't damaged.
And check to see if the Light Blue wire with a single, capped off plug, by the 7 pin trailer plug isn't damaged.
I had brake lites blowing fuses on my 04 just before I traded it. The wiring harness to the rear runs along the outside on the frame and then up over the rear cab mount and back down along the frame. The wiring harness had rubbed and wore thru at the cab mount and was grounding. 3 or 4 wires were bare in that spot, one being the 12V trailer power ( it makes big sparks when it's bare).
Just slide under the driver's back corner of the cab and you will be able to tell if the harness has rubed thru. Just a thought hope it helps.
Just slide under the driver's back corner of the cab and you will be able to tell if the harness has rubed thru. Just a thought hope it helps.
First, thanks all for the suggestion s and heymccall for the wiring diagram. I was really looking for a schematic for the chmsl circuit. All connections are clean tight and well made. Didn't find bare wire between the cab and the bed. What does the small blue wire with the cap next to the trailer jack do? It's OK and just hanging there. Here is what I did. I ran a new 7 pin trailer jack left side forward of the wheel so I can also use the jack for my cabover camper. I used factory made 7 conductor cord. 12V red and Trailer blue are 10GA. The rest are 14GA. I used 3-M locks that pinch thru the insulation for contact using the correct connector for the gage of wire. Since I was having intermittent trouble I connected the trailer brakes blue wire using a yellow wire nut. That way the next time I had trouble I could open the wire nut and that would eliminate my trailer and my wiring to the jack as the problem. When it happened this time I opened the blue at the wire nut and I still blow the fuse. Tried a 15A and still blow the fuse. I was still on the road and I went under the dash left side where the prodigy controller plugs in and I found I could remove the whole block by depressing two ears. I pulled the block out as far as I could and didn't see anything wrong. BINGO trouble came clear. I hope this solved the problem but as in the past the trouble comes and goes and I don't know for sure what I did exactly to clear it. Back to the schematic. If I knew from the back of the block where the blue wire goes and where the junction is for the cab tail lite so I could open it there it would help so I could isolate to a section like between the block under the dash and where that junction is. Is there such a schematic that someone can share?
Regards,
John
Regards,
John
My CHMSL problem has been solved.
My 5th wheel harness rubbed through between the box and the fender.
My 5th wheel harness rubbed through between the box and the fender.
that small blue wire with the cap next to the trailer plug is a rear chmsl wire, you should also have one at the camper plug. if you have a camper or a cap with a top brake light , you use this wire or if you have a pull behind trailer with a top brake light you can use this wire. I think you should check your camper plug to make sure it is wired correctly. just my thoughts again===charlie
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