Major Short

[Jeide]

Hello All,
I’ve got a 2000 Ranger with the 3.0 flex fuel option. It’s been running great for quite a while now. I ran it for a quick trip to the store yesterday. It made it there and back just fine. About 5 hours later, I got in to start it and nothing. Less than nothing, no dash lights, no clicks, no buzz from the fuel pump. I got out and metered the battery and it measured less than a volt. I took both leads off of the battery posts and metered across the leads and read a short. I’m okay with a meter and the principals of troubleshooting a circuit but have no idea where to begin here. I checked all of my fuses inside the cabin. I haven’t checked the fuses under the hood yet, but will do that next. I would think that a short of this nature would have left melted wires and a smell behind or something. I would also have expected it to blow a fuse leaving behind no measurable short between the battery leads. Any help would be appreciated.

 

[RonD]

Always check the fuses in the engine bay fuse box first, they feed power(12v) to the cab fuse box fuses

In the diagrams below:
Battery Junction box is in engine bay
Central Junction box is in the cab

The larger AMP engine bay fuses feed power to several cab fuses, so if you pull a 50amp fuse and no short, then you know the issue is on that circuit

From your description you know this drain in NOT on a Key on circuit, it must be on a full time power circuit for battery to drain when vehicle was sitting with key off

There are very few full time power circuits so focus on those
But pretty much ALL the the engine bay fuses have full time power, so check them all, as one of their wires could be shorted

If battery was under 8volts it's toast, will never hold a charge for very long again, and will be self draining even when unhooked
Check the Alternator wires

 

[Jeide]

Thank you RonD. I got around to the fuses under the hood and found the 10 fuse blown which it shows is the horn. I believe that the speed control also uses this fuse. At this point I have no voltage to measure current. I can’t even light a test light. I’m just metering resistance.

 

[Jeide]

Another update: I’m getting closer. So I pulled the fuses under the hood a row at a time until the meter no longer read a short. At that point I had 4 fuses out. I plugged them back one at a time until I got a short. Turns out the short went away with both fuses 11 and 12 pulled. What those have in common is the main light switch. Is that the head light switch on the lower dash to the left of the steering wheel?

 

[RonD]

With fuse 10(15amp) out one terminal should read 12v with battery connected, or whatever battery volts are left

This voltage goes to the Horn Relay(#7), pull it out
Put new 15amp fuse in and see if it blows
It Shouldn't
If it does then short is inside the engine fuse box

Test Horn relay with OHM meter

Might be this type of relay: https://www.gtsparkplugs.com/images/micro-automotive-relay-wiring.jpg

Ford uses numbers 1 to 5 instead of the original Relay numbering
1 = 85
2 = 86
3 = 87
4 = 87A(not use on most relays)
5 = 30

So key off slots 1 and 5 should read battery volts with fuse 10 in place
Confirm this because Ford often reverses 1 and 2 and 3 and 5, since it doesn't matter to operation but WILL matter for testing

Relay pins 1 and 2 should show 50-200ohms, just a coil of wire inside
3 and 5 should show No Connection

Test slot 1(relay base) should be battery volts if so then slot 2 goes to the Horn button on steering wheel
Horn button GROUNDS slot 2 to activate the Horn Relay
Test if that happens

 

[Jeide]

Thank you. You are right. In my case both 1 & 2 are swapped and 3 & 5 are swapped. I’m metering continuity to positive lead instead of voltage due to condition of battery but should get correct results. Pins 1 and 2 have 81.2 ohms across them 3 and 5 have no connection. In my case slot 1 goes to horn switch. Slot 1 to ground shows no connection unless horn button is pushed, it then shows a short. Good so far.

 

[Jeide]

Sorry for the delay, I’ve been meaning to update this thread. I did finally figure it out. After I confirmed the horn circuit was good I still had a short and it seemed to only go away with the main light switch and muti-purpose switch fuses removed.(?) They both have a common lead so I figured it must be that. I tried to trace the wires behind the dash but gave up and decided that I would just replace that wiring. Well shortly after starting that process, I metered the battery leads again expecting the short to be gone since those circuits were cut short at the dash. Well it was still there. Well not there but back on the horn circuit. It seemed to be jumping around. I began to suspect the junction box. I should mention that a couple months ago, while chasing a different problem, I had broken the plastic tab on the junction box that holds the mega fuse because I didn’t know how it came apart. This time, when I got the junction box apart I found that the plastic tab was attached to the metal plate inside the box that feeds power to most, if not all of the fuses. That tab being gone let the plate move around a little inside and I think that it finally moved enough with vibration and temperature and whatnot that the plate started touching stuff that it shouldn’t. I ordered a replacement and installed it and it started right up and has been running great ever since. I hope that this experience helps someone.