Intermittent short Grrrrrr

[Dihrdbowti]

I have an intermittent short that just showed up. When I put the truck in reverse it pops. It's fuse 16 and handles both the turn signals and reverse lights. When it first popped I was on a two week camping trip with my son and I was on my way back home. All I had was a 25 amp so I put that in in place of the 20. Yeah I know bad Phil. Anyway I got home got a box of 20 amp fuses and started tracing the lines. It only pops when I put it in reverse. so I worked on the wires on the opposite side of the neutral safety/backup switch. I found a short close to the rear of the truck that I fixed but it still pops the fuse again only when it goes into reverse. The only thing I can think is that the neutral safety/backup switch is the culprit. With the fuse removed I measure about 7K ohms to ground at the fuse when in reverse. Just an FYI when the fuse has popped I still have emergency flashers but not turn signals. For the past couple of days what I have been doing is pull the fuse to back out of a spot then open the door and put it back so I can have my signals. I occasionally leave the fuse in and might get a few hours of running around before it pops and sometimes it pops every time. Any ideas or troubleshooting hints? Oh just for the hell of it I replaced the reverse lights. the lights in there (and have been since I bought the truck 2 1/5 years ago) were the same as the turnsignal/brake running lamp.

[a5150nut]

Have you got reverse lites wired thru a trailer connector? Maybe moisture inside of receiver? Just a first thpought...........

[JohnC]

Get a bulb like a 1073 and solder 2 wires to it, or get a bulb from U-haul with pigtails already on it. Plug the two wires in in place of the fuse. Put it in reverse and start fussing with the wiring. When the bulb gets full bright you've hit the short...

7K ohms too ground is nothing. you're looking for more like .07 ohms... It has to be less than 0.6 ohms to overdraw a 20 amp circuit at 12 volts.

[stingthieves]

Get a bulb like a 1073 and solder 2 wires to it, or get a bulb from U-haul with pigtails already on it. Plug the two wires in in place of the fuse. Put it in reverse and start fussing with the wiring. When the bulb gets full bright you've hit the short...

Guess I have been living under a rock all these years!
Thanks John

[Dihrdbowti]

Have you got reverse lites wired thru a trailer connector? Maybe moisture inside of receiver? Just a first thpought...........
No I don't have reverse lights wired. I saw that in the schematics though and suppose I need to try and trace that wire as well.



Get a bulb like a 1073 and solder 2 wires to it, or get a bulb from U-haul with pigtails already on it. Plug the two wires in in place of the fuse. Put it in reverse and start fussing with the wiring. When the bulb gets full bright you've hit the short...

7K ohms too ground is nothing. you're looking for more like .07 ohms... It has to be less than 0.6 ohms to overdraw a 20 amp circuit at 12 volts.

Great troubleshooting tip. I completely forgot about that.. looks like I will be doing that tonight..

My thoughts as well. Which is why I thought I found it in the wiring close to the light bulb itself (measuring .02 to ground). Just before leaving for work this morning I hooked up my DVM to check the current. I set it up to capture and got 51.3 amps when the fuse blew. Holy frijoles... And of course when I replaced the fuse it was working fine. Grrrrrrr... ok tonight I should have time to get into the wiring..

Thanks for the tips and suggestions

[tommac95]

sounds like you're on track.

somebodies found wires deteriorating by movement of steering columb tilt, maybe check that area and shifter movement....

[Dihrdbowti]

Well I think I have the area. I took one of the turn signal, brake, running lights and ran it across the open fuse. I put it in reverse and it came on real bright. I started messing with wires all the way from the back through the neutral/backup switch then to the main harness connector at the firewall. As soon as I grabbed the wire loom the light went out. I'll be damned if I can't get the short to come back. It's not blowing fuses but now I don't have my backup lights... Arrrgggg... well it gives me something to do.. Guess I need to try and figure out how to take that connector apart and trace the lines. Anyone ever take one apart?? :)