Stumped by short to ground

[TRevs]

Since I got the YJ, the heater blower motor hasn’t worked. I don’t mind that much but it would be nice on a chilly day, and would increase the odds my wife will agree to ride in it.

I finally decided to try and figure it out. I have virtually no experience in automotive wiring, but like everything else I’ll try to learn.

I checked the fuse and sure enough it was popped. I replaced it and as soon as the ignition key went to ON the fuse popped again. I disconnected the battery, and used the mulitmeter to test for continuity from each of the fuse terminals to Ground. From the left terminal there was no circuit , but from the left terminal there was low resistance. I removed the heater controls and from my rudimentary understanding of the wiring diagram, found the dk green wire going to the heater on/off switch. I tested the end of that wire and also got continuity to ground.

I was feeling pretty smart at this point because I’d identified the damaged wire, so I removed all the gauges/bezels on the dash to inspect the course of the wire.

I’ve looked it over back and forth many times and can’t see any place where the external insulation or plastic loom is damaged.

Where else could the short be? Could it be inside the wire bundle itself without touching the chassis?

I don’t want to rip out the entire wiring harness and open it up unless I have to. It would seem easier to run a new wire and bypass the fault.

 

[TRevs]

 

[machoheadgames]

Many times the blower motor itself goes bad and shorts the system. You haven't replaced the blower motor, right?

If it were me, I'd depin the blower motor connector (on top of the lower heater box behind the glove box), then hook up some alligator clip leads to the wires going to the motor and then run those to a battery. Put a fuse on the positive so that you don't cause an unfused short and burn the Jeep down. See if the motor powers on, if it doesn't, it would have blown the fuse again, if it does then you still have a wiring problem hidden somewhere. It is quite a simple wiring diagram, so other than the power wires being tucked in the loom from the battery all the way to the bulkhead on the firewall, it shouldn't be that difficult to find the problem.

I've attached the blower motor wiring diagram just in case you aren't already referencing it.

 

[TRevs]

I haven’t done anything with the blower motor yet. I hadn’t even gone downstream from the controls (although I did inspect the resistor because it was so accessible) because I got continuity to ground from either end of the dk grn wire:

I figured if there is any problem downstream of that I’d tackle that later but if I fix this short I might be done. If I’m reading it correctly the short should be under the dash, before the heater control switch. So I wasn’t tracing anything from the battery / PDC to the firewall, although I did inspect all the cables a bit.

I guess I need to open the loom and trace the wire the whole way; does removing the entire dash make it easier to access? I’ve only removed the gauges and their bezels thus far.

 

[machoheadgames]

I read your post too fast. Based on your findings I don’t think the blower motor has any part of it. Especially if turning the key is killing the fuse even with the blower motor switch off.

To dig into the loom, removing the metal dash panel helps a lot, because of how the loom is routed over the steering column. Going to be hard to fish it out with the dash panel still in place. I can see the appeal to running your own bypass wire, though it may be difficult to do that cleanly, especially if you’re trying to hook it up to the back of the fuse box like stock.

 

[TRevs]

, removing the metal dash panel helps a lot, because of how the loom is routed over the steering column. Going to be hard to fish it out with the dash panel still in place.

I was afraid you were going to say that. I’ll probably put it off awhile since I won’t need a heater for 6+ months down here. I’m sure it isn’t too bad to remove the entire dash but I need to get the Jeep back in service for our nice spring weather.

 

[machoheadgames]

I was afraid you were going to say that. I’ll probably put it off awhile since I won’t need a heater for 6+ months down here. I’m sure it isn’t too bad to remove the entire dash but I need to get the Jeep back in service for our nice spring weather.

It’s not “hard” to remove the dash but definitely a pain. Hardtop has to be lifted if you have one, windshield goes down, lots of (different) screws, glove box comes off, dash pad comes off, steering wheel has to come off to get dash panel off.

None of it is difficult, but it’s all annoying and it is a lot of parts to keep up with. With summer coming up, I’d enjoy the weather and curb this project til Octoberish. In the meantime, put your HVAC on “VENT” and enjoy the koolbreeze drafting in.

 

[TRevs]

I’ve begun to track down this short again, and am still getting continuity to ground from the right terminal of the fuse, with the dark green wire. (Circled red on the diagram). Looking at the rear of the fuse box, that terminal has a bridge to an unused terminal just above it, represented by the black bar circled green on the diagram.

Both dark green wires head up in the loom over the parking brake pedal and into the dash.

Why are there two wires bridged at the back of the fuse box? Both are labeled C1 on the fuse box diagram, but in the Heater circuit diagram, it shows only one Dk Grn wire leaving the fuse box.

So confusing…

 

[machoheadgames]

I’ve begun to track down this short again, and am still getting continuity to ground from the right terminal of the fuse, with the dark green wire. (Circled red on the diagram). Looking at the rear of the fuse box, that terminal has a bridge to an unused terminal just above it, represented by the black bar circled green on the diagram.

Both dark green wires head up in the loom over the parking brake pedal and into the dash.

Why are there two wires bridged at the back of the fuse box? Both are labeled C1 on the fuse box diagram, but in the Heater circuit diagram, it shows only one Dk Grn wire leaving the fuse box.

So confusing…

View attachment 122250

All of the black bars are jumpers. They go to unused open terminals so that if you ever needed to tap power, you could do so by inserting a spade terminal into the slot. So essentially the spot at the top of the green circle is just a slot for a spade that would receive RUN power when key is set to run. That circuit is powered by the black/orange wire that comes from the ignition switch.


When you were popping fuses, was the dark green wire hooked up to both sides of the heater switch on the control panel, and was the heater turned on?

 

[TRevs]

When you were popping fuses, was the dark green wire hooked up to both sides of the heater switch on the control panel, and was the heater turned on?

I stopped putting in fuses after I popped one new one. At that point everything was still connected. The dk green wire would have been connected to the heater switch, but I don’t know what position that switch was in at the time.

 

[machoheadgames]

I stopped putting in fuses after I popped one new one. At that point everything was still connected. The dk green wire would have been connected to the heater switch, but I don’t know what position that switch was in at the time.

Reason I ask is because determining when the fuse pops (switch set to on vs off) could help find where the short is that’s causing the problem. If switch was off, the short is likely between the control panel and the fuse panel….but since you said that harness looks pretty clean and untouched, that makes me think maybe the switch was flipped and you have a problem somewhere downstream of the switch. Which in that case the blower motor, blower motor resistor, or wiring between those parts and the control panel could be where the problem lies.

 

[TRevs]

Appreciate all the info and advice!

I disconnected the connectors from the back of the blower on/off switch, the fan speed switch, and to the blower motor itself. My son has a power supply for his electronics hobbies so I put 12v 12 amps onto the blower motor and it fired right up and ran normally (pretty exciting I thought at the time; it probably hasn't run in years).

Then I reconnected the negative battery terminal, left all the circuit connectors disconnected, put a new fuse in the block, and turned the key to ON. The fuse immediately popped.

So, I conclude there is a short to ground between the fuse block and the connector for the blower on/off switch.

 

[TRevs]

Last time I traced the wires from the control panel side a foot or so back to the left before they go over the steering column. I didn't open the loom much, but I didn't see anything that looked like damage.

This time I'll start from the fuse block side; there looks a lot of potential for wire damage up there above the parking brake.

 

[TRevs]

3: I have an external Power pack (bench supply DC) I use it on this path with cab fuse blower pulled. and power it up see the huge short, fan not connected
then I disconnect the all connectors in the path right to left. when the short ends, the bad section of wire is know known.

how do you set this up? One probe in the fuse terminal and the other to metal ground like the dash?

How many amps? Lowest possible?

 

[deadpool1]

C1 to C7 is 14AWG and fuses at 25amps
it can handle 10 amps all day long. even more really
to do the tests use a 1 to 10 amps power supply, F12 pulled.
I'd use 1amp or at the most a 5amp battery charger.

 

[deadpool1]

lots of ways to skin a cat, said grandpa. F12, 25amp fuse keeps blowing.
buy a whole new harness , oops none sold now, only used. and scalper prices. (nah)
fuse F12 cab blows, and but not with , 2 wire connector is disconnected at the blower it self . so is not the blower shorted.
steps to find it , ordered list, not wanting to blow a box full of fuses trying to find it, (a given?)
well use thermal breaker in F12 slot, a CB? sold in all auto stores it is. ATC size or do my list below.

1. Main battery NEG lug pulled and Isolated. (wrapped in say a clean rag)
2. F12 pulled
3. connect a DC power pack, power supply, or tiny battery charger to this F12 socket on the output side. (+12vdc power wire wire)
4. connect DC power pack (-) to ground to body ground.
5. turn on said DC power pack . (what does it do now?)
6. See it overload, even uses meter to read the voltage at F12 output.
7. pull connectors to from the right side , to the left 1 by 1 until the short is gone, (you see 12vdc so is not shorted now)
8. now you know what section of harness (UK LOOM) that is shorted. C1 or C1 or C7 wire. or the switch , or the resistor block is shorted.
9. done. ( examine the found bad harness section carefully, you will find it shorted)

Before starting, we test the power pack first (zillions of kinds made and sold)
tests first this:
short the power pack clips first to see what it does shorted. ( sorry they are not all the same)
some blow up now and are now dead, for ever (china $5 power packs?) even Lets the smoke out. bad.

or just goes to overload and its gauge pegs or lamp LED glows "overloaded" and or shorted. GOOD !
or like mine, I dial up 1amp 12vdc and if shorted it pushes 1full amp when shorted all day or week long. endless. and 100% NO HARM done !
this or any 12vdc pack that does not blow it self up, shorted, and a DMM set to Volts connected across the two 12vdc pack wire connections.

ignore the yellow jack, use + and - only , plus to fuse F12 and - minus to car body.

 

[deadpool1]

By the way 1:
Post #2
my harness looks nothing like yours, at all. mine is 95
has yours been hacked?
I can see my green wires here. going to the main harness. or is mine hacked?

 

[deadpool1]

93 YJ, but not once told i car has A/C option. why?
it does matter.
mine is heat only HVAC, and then I put A/C in mine (non OEM A/C)
what options on the car matters.
as does mods and hacks, someone run long bolt/screws behind and or above the PCM on the fire wall and short the fuse box out?
if the car had factory A/C day 1 this is the wring page that can short
AS you can see it has TWO, DG, dark green wires. at C1 lug of fuse.
and the connector, A to D below is there and if hacked or AC removed by cutting and hacking wires to that connector, it will short.
even if dash Hvac panel shows no a/C mode. it may have AC/ hacks done to the car.
the FSM covers all this and is free. and in the sticky. just 1 more possibility.

 

[TRevs]

Update:

I've solved the short, sort of. I traced the green wires that both use the lug at the back of the #12 fuse; the '95 4.0 L wiring diagram looks a bit different than the one above, but they start the same out the back of the fuse. The short is definitely on the A/C side of the circuit, probably Z1 after leaving the connector for the A/C blower.

My Jeep apparently did not have A/C from the factory ("Air Conditioning Bypass" is printed on the build sheet), but somewhere downstream is the short. Visually I don't see anything that looks like prior-owner hackery or cut looms, but rather than trace the end of a circuit I don't use, I cut the A/C C1 dkGrn wire a few inches behind the fuse, and the short in the heater blower circuit disappeared.

I may eventually put A/C in, so I'd presumably have to chase down the short completely at that time, but hopefully I can at least get heat going since winter has arrived. (And hopefully I haven't damaged anything else in the process of disassembly.)

 

[machoheadgames]

I forgot about that AC plug. It should be chilling unused up under the dash and probably zip tied to the steering column or somewhere in that vicinity. I talked about it on here ages ago. It has like 6 wires on it and shares blower motor power from the heater blower motor power. totally forgot about that.

And what I also forgot to mention is that that circuit goes to a diode that goes to ground, as shown in your clip of the diagram. I still don't understand the point of that but there was a guy who kept shorting that circuit a few years ago and his diode had gone bad. That is probably where your problem is. If not, then the green wire may be shorted to metal somewhere between the fuse panel and the AC connector.

For what it's worth, aftermarket AC will typically just hook up to the fuse panel with a power wire and then run its own wiring to the compressor. It won't go through all he factory wiring. So if you decide to add AC, you pretty much won't need that green wire anyways. The only downside to that is the factory method runs the AC activation through the PCM so it can bump the idle for smoother performance. If you do it the aftermarket way then it's sort of a drain on the electrical system and the PCM won't bump the idle or anything to smooth it out because it doesn't realize the AC is on.

All that to say the problem is definitely solved for now, and later you may or may not need the green wire depending on A) if you decide to actually add AC and B) if you hook it up the factory way vs aftermarket. I believe the only one selling a factory hookup style is Nostalgic Air Parts. JeepAir from what I have seen has you hook it up to the fuse box only.