Mux/t Tow Fuse Circuit Causing Drain

[Country Pop]

My father has a 1995 Jeep grand Cherokee that drains the battery every few days. I draw tested the battery and it is fine. The alternator is charging fine. During a check of the circuits for battery drain, I found that the MUX/T Tow 50 amp fuse is draining the battery at a rate of about 1.5 amps or more. The manual I have does not list the fuse so the following questions come to mind.

1. What circuits are on this fuse?
2. Can the truck be safely operated without this circuit?
3. What further can you do to detect the trouble?

Some answers I came up with after a little more checking.
1. The gage cluster does not work when the fuse is removed, it must be on this fuse. None of the cluster system lights come on when this fuse is out. The cluster illumination lights work ok.
2. All external lights work without the fuse in except stop lights.
3. All other functions are working without the fuse in.
4. No the truck cannot be safely operated. See answer #1and 2 above
5. Found online that a check of any trouble codes might determine touble.
6. No codes were found. But i ddid have the battery cables off before this was checked. He is going to drive it home and back on Sat so I can recheck the codes.
7. Many replys to other posts here on this site refer to the MUX as a "multiplexer"

More questions
1. What the heck is a multiplexer?
2. What relay controls the cluster? Or is this done directly by the ECM.

I do have a good background in electrical and electronic circuits of many types, mostly radio and computer, but also including automotive. So feel free to beat me up if I am overlooking the obvious. I just feell like I am beating my head against the wall here.
AND this is what it feels like (thought that was real cute)
Any help or ideas I have not persued would be greatly appreciated.
Thanks in advance.
73 de Country PoP

[quarkdude]

Originally Posted by Country Pop

My father has a 1995 Jeep grand Cherokee that drains the battery every few days. I draw tested the battery and it is fine. The alternator is charging fine. During a check of the circuits for battery drain, I found that the MUX/T Tow 50 amp fuse is draining the battery at a rate of about 1.5 amps or more. The manual I have does not list the fuse so the following questions come to mind.

1. What circuits are on this fuse?
2. Can the truck be safely operated without this circuit?
3. What further can you do to detect the trouble?

Some answers I came up with after a little more checking.
1. The gage cluster does not work when the fuse is removed, it must be on this fuse. None of the cluster system lights come on when this fuse is out. The cluster illumination lights work ok.
2. All external lights work without the fuse in except stop lights.
3. All other functions are working without the fuse in.
4. No the truck cannot be safely operated. See answer #1and 2 above
5. Found online that a check of any trouble codes might determine touble.
6. No codes were found. But i ddid have the battery cables off before this was checked. He is going to drive it home and back on Sat so I can recheck the codes.
7. Many replys to other posts here on this site refer to the MUX as a "multiplexer"

More questions
1. What the heck is a multiplexer?
2. What relay controls the cluster? Or is this done directly by the ECM.

I do have a good background in electrical and electronic circuits of many types, mostly radio and computer, but also including automotive. So feel free to beat me up if I am overlooking the obvious. I just feell like I am beating my head against the wall here.
AND this is what it feels like (thought that was real cute)
Any help or ideas I have not persued would be greatly appreciated.
Thanks in advance.
73 de Country PoP

Hello Country Pop,
I too am having the same exact problem with my 1998 Jeep Grand Cherokee Laredo, 4x2, 6 cylinder. I pulled the 50 amp Mux/T tow fuse and got the same results ( from the fuse box in the engine compartment ). I also found that if you pull fuse #7 (cluster fuse ) from the fuse box in the passenger area under the glove box and to the right ( passenger kick panel ) the current draw goes to zero, but your instrument cluster wont work either. I took everything out of the dash hoping that when the item causing the short was pulled the current draw would go away. I pulled the insturment cluster, the headlight switch box, the O/D and defroster switch box, the radio, the cigarette lighter connector and the accessory power connector and still the current draw is there. I havent found the answer yet, if anyone is out there that knows how to fix this, could you share what the fix it? I also changed to Alternator which didn't fix the problem. I also unplugged all 3 computer connectors ( computer is located on the passenger side firewall in the engine area ) still the current draw was there, so the computer isn't causing it.
...........HELP!!!! Quarkdude

[cturnbull802]

Originally Posted by quarkdude

Hello Country Pop,
I too am having the same exact problem with my 1998 Jeep Grand Cherokee Laredo, 4x2, 6 cylinder. I pulled the 50 amp Mux/T tow fuse and got the same results ( from the fuse box in the engine compartment ). I also found that if you pull fuse #7 (cluster fuse ) from the fuse box in the passenger area under the glove box and to the right ( passenger kick panel ) the current draw goes to zero, but your instrument cluster wont work either. I took everything out of the dash hoping that when the item causing the short was pulled the current draw would go away. I pulled the insturment cluster, the headlight switch box, the O/D and defroster switch box, the radio, the cigarette lighter connector and the accessory power connector and still the current draw is there. I havent found the answer yet, if anyone is out there that knows how to fix this, could you share what the fix it? I also changed to Alternator which didn't fix the problem. I also unplugged all 3 computer connectors ( computer is located on the passenger side firewall in the engine area ) still the current draw was there, so the computer isn't causing it.
...........HELP!!!! Quarkdude

same problem x3.... 5.9 limited.

anyone have a fix? its obviously worth posting with 3 ZJ's with the same problem!

[xj31]

If you have a trailer hitch,look at the connector for the trailer wiring.I have seen some with a bunch of corrosion and they caused some weird electrical problems.

[cturnbull802]

Originally Posted by xj31

If you have a trailer hitch,look at the connector for the trailer wiring.I have seen some with a bunch of corrosion and they caused some weird electrical problems.

by the fuse lable you would think that would be it.... but its not
its the ZJ mystory short.

i read somewhere (i think cnet) to pull the gauge cluster and inspect the traces on it for any burn marks. i havent pulled mine out to look yet.

[quarkdude]

Originally Posted by cturnbull802

by the fuse lable you would think that would be it.... but its not
its the ZJ mystory short.

i read somewhere (i think cnet) to pull the gauge cluster and inspect the traces on it for any burn marks. i havent pulled mine out to look yet.

Hello cturnbull802,

My ZJ is still shorting out somewhere. Since I cant seem to find the short, I am going to Harbor Freight to purchase a $15.00 solar panel that plugs into the cigarette lighter and see if that will keep the Jeep alive for starting for more than 2 days of sitting there. Hopefully the current output of the solar panel is greater than the current draw of the short, if so, it should keep the voltage at a point where it should be without a short.
............quarkdude

[quarkdude]

Originally Posted by xj31

If you have a trailer hitch,look at the connector for the trailer wiring.I have seen some with a bunch of corrosion and they caused some weird electrical problems.

Hello xj31,
I checked the hitch connections - though the hitch that is on my ZJ is a uhaul after market one. The original wiring was pretty bad, so I changed the wiring harness with a new one. Checked ground to ground continuity and it is good. Checked power to ground for shorts - none seen. Ohh well, I'll keep trying new ideas as I keep going thru the vehicle electical areas.
............Thanks, quarkdude

[cturnbull802]

i went out today and bought a 5 post relay. my plan is to wire it so the mux/t tow curcuit is open when the key is out



untill i can figure out what is drawing down the battery

[quarkdude]

hello all,

I could not find the short anywhere. I did have a Walmart Battery that had a warranty and I replaced it twice in a 6 month period and still had the same problem. Finally I threw my hands up and broke down and bought a real battery - an OPTIMA battery from Costco. Cost $120.00 which was a good deal on a red top Optima. Seems to be that the short is gone now. Have let is sit for more than 2 days and it starts now. Maybe the Walmart batteries I had before had on internal short inside them that was very hard to find. All I can say is it works now with no battery drain.
Maybe this will help some of you out there that have this issue.
........Thanks, quarkdude

[cturnbull802]

Originally Posted by quarkdude

hello all,

I could not find the short anywhere. I did have a Walmart Battery that had a warranty and I replaced it twice in a 6 month period and still had the same problem. Finally I threw my hands up and broke down and bought a real battery - an OPTIMA battery from Costco. Cost $120.00 which was a good deal on a red top Optima. Seems to be that the short is gone now. Have let is sit for more than 2 days and it starts now. Maybe the Walmart batteries I had before had on internal short inside them that was very hard to find. All I can say is it works now with no battery drain.
Maybe this will help some of you out there that have this issue.
........Thanks, quarkdude

bad news for you... i am on my 2nd optima and my jeep keeps dieing

[mspan90]

There is a 20amp fuse inside jeep on passenger kick panel. First one closest to firewall. Pull that and If the drain goes away you have a bad BCM I THINK. I wired a switch in line between that fuse and the BCM and I cut the switch off when i cut off the key and all is well so far. I wasnt willing to spend$300 on a new BCM.

[Erikconsersave]

Ok guys this is a very old post but I'm still having this problem in 2016. The mux/t tow fuse can be traced to passenger kick panel fuse #7. It then goes to the BCM. The BCM controls the windows, ins cluster and the rear latch and window latch. Unplug wiring harness' from the BCM until the voltage drop goes away. Most drains have been traced from the bcm to the rear latches, the driver and passenger door modules (window switches) and the overhead console. Try unplugging wire connectors from the rear lock, rear window lock, the driver and passenger doors and the overhead console. Unplug these 1 at a time while u monitor the voltage drop with test light/multimeter in line between the negative terminal and negative battery post. When the voltage drop goes away u have located the bad part and u can replace it or leave it unplugged. Hope this helps