This is on my old '96 1500 5.9L. Been messing around with this problem for almost a year, but now the 15A blue fuse blows almost every other day, so I need to get to the bottom of it since my teenager is driving the truck now. When replaced, it will work for a while before blowing. Sometimes the ABS/Brake light will come on too, but not every time so not sure if it is related. I've replaced the brake switch a few times. I'm not towing anything. Probably wire shorting to ground or something, but not sure where to look. Any ideas where to start?

 

uh u got a short, thats not going to be fun, do you have a multimeter

 

Yes, I have a multimeter, just need to know where to look first.

 

haha with a short you never know start at your taillights and work your way back

 

Would be easier to check if it was shorted all the time...the short is intermittent and only blows while driving due to vibration I assume. Anyone have a wiring diagram type thing that shows where the brake light wires are located as they travel down the chassis to the fuse box and ECM?

 

good point and sorry no i dont but hopefully someone does,

 

remove the brake lights and check bulbs and sockets. make sure there's no corrosion or water or gunk in the sockets. check the wires for damage insulation. check any trailer wiring. if you have a trailer connector, remove it and see if the problem goes away.

 

Try making a test light setup to take the place of the fuse that is blowing. Use the blades from a blown fuse and solder on 2 pieces of wire about 6 feet long to a bulb socket and bulb. Plug the tester into the fuse holder and put the bulb under the truck where you can see it. Then start wiggling the wire harness that runs to the rear bumper area. When the bulb lights you have found your problem location. Be patient, turn, twist and slide the harness every way you can since the problem is being caused by chafing during operation and the static harness will not show the problem. Be careful to check any area the harness goes inside the chassis rails as these are more prone to chaffing. You may need to have the ignition on if the brake lights don't go on with the ignition off. The bulb loghts because of current flow caused by the harness grounding which normally would blow the fuse. Since the light is in place of the fuse it lights due to the current flowing to ground.

 

APA228 is spot on !!........ you can buy a tester from harbor freight and tools, it is a circuit breaker that takes the place of the fuse , so instead of blowing fuses the breaker will open and cause a light to go on, the APA 228 method will work perfectly also, here are some places I have found shorts on that particular truck

#1 rear mounted stop light, the factory only put a hair of silicone to seal that , and usually it fills with water, I have seen them actually light up with water in them

#2 steering column with tilt steering , put in a fuse ,or wich ever method you like, the fuse one is really not good, but any way, tilt the wheel several times up and down see if it blows the fuse,

#3 as stated above so MANY bad trailer wirings, those inline "T" connectors, do this remove and try, good luck and let us know

 

Used some spare time over the holidays to try and isolate the problem. There was some moisture in the 3rd light, but it wasn't it. Then removed the rear lights and found that the wiring harness that was attached to the fender by a plastic fastener had come off and pulled a section of unprotected wire through the metal fender hole and wore the brake light wire to bare metal, thus shorting to ground when vibrating.

I wrapped the wire with electrical tape, and pulled the plastic harness wrap over the section that goes through the fender wall, reattached the fastener and have had no fuses blown in 2 weeks now.