battery charging issues & 50A MUX/T Tow Circuit - JeepForum.com
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post #1 of 11 Old 03-15-2020, 03:46 PM Thread Starter
Rick1955
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battery charging issues & 50A MUX/T Tow Circuit

1997 jeep Grand Cherokee.
Symptoms: 1) Battery not at a full charge rate. 2) Current drop of 3.5A on 50A MUX/T Tow fuse circuit. Are these two related?

Here is what happens: Starts fine. Voltage indicator on dash shows 14V, immediately drops to 11.5V, then after a couple of minutes it flat lines to zero volts, then eventually pops back to 11.5V & repeats this cycle from 0 to 11.5V.

Battery: Fairly new, new post clamps. Multimeter shows 12.3V when battery is disconnected. 11.8V when cables are connected. 11.75V when engine is running.

Alternator: New. Then re-tested at Schucks & Autozone...they said it is good. Schucks said they will not replace if they test it good. Voltage drop on neg side is zero volts. Voltage drop on pos side to B+ is 1.5V

Replaced my PCM also. ouch$$$

Is my new alternator really bad or could my 50A MUX/T Tow circuit be affecting the charge? I like to figure things out myself before taking to an expert mechanic, but, perhaps it is time to take it in. Any suggestions? p.s. thank you in advance! You guys have already been a lot of help!

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post #2 of 11 Old 03-15-2020, 03:58 PM
GOLDWING
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Quote:
Originally Posted by Rick1955 View Post
1997 jeep Grand Cherokee.
Symptoms: 1) Battery not at a full charge rate. 2) Current drop of 3.5A on 50A MUX/T Tow fuse circuit. Are these two related?

Here is what happens: Starts fine. Voltage indicator on dash shows 14V, immediately drops to 11.5V, then after a couple of minutes it flat lines to zero volts, then eventually pops back to 11.5V & repeats this cycle from 0 to 11.5V.

Battery: Fairly new, new post clamps. Multimeter shows 12.3V when battery is disconnected. 11.8V when cables are connected. 11.75V when engine is running.

Alternator: New. Then re-tested at Schucks & Autozone...they said it is good. Schucks said they will not replace if they test it good. Voltage drop on neg side is zero volts. Voltage drop on pos side to B+ is 1.5V

Replaced my PCM also. ouch$$$

Is my new alternator really bad or could my 50A MUX/T Tow circuit be affecting the charge? I like to figure things out myself before taking to an expert mechanic, but, perhaps it is time to take it in. Any suggestions? p.s. thank you in advance! You guys have already been a lot of help!
If your "new post clamps" have the cable pinched between a piece of tin and the actual clamp, get rid of them. If you have crappy cables and dirty corroded ground points on the engine and body/chassis then take care of them. After that you may find that the new PCM was not needed.

GW

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post #3 of 11 Old 03-15-2020, 04:21 PM Thread Starter
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Thank you GW. I do have the tin clamps, will fix this. Cables & grounds are ok.
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post #4 of 11 Old 03-15-2020, 07:21 PM
StPaul59
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Quote:
Originally Posted by GOLDWING View Post
If your "new post clamps" have the cable pinched between a piece of tin and the actual clamp, get rid of them. If you have crappy cables and dirty corroded ground points on the engine and body/chassis then take care of them. After that you may find that the new PCM was not needed.

GW

Good God I hate those clamps with a burning passion!
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post #5 of 11 Old 03-15-2020, 07:47 PM
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Good God I hate those clamps with a burning passion!
I think that they are maybe good enough to get you home if you somehow have a problem on the trail. Beyond that, they allow lots of mechanics to earn easy money since they can cause symptoms that mimic all manner of expensive issues.

GW

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post #6 of 11 Old 03-17-2020, 06:37 PM
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Quote:
Originally Posted by GOLDWING View Post
If your "new post clamps" have the cable pinched between a piece of tin and the actual clamp, get rid of them. If you have crappy cables and dirty corroded ground points on the engine and body/chassis then take care of them. After that you may find that the new PCM was not needed.

GW
Could you clarify this clamps story? I have some issues with my battery charging and I use clamps like this: could they be the problem?
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post #7 of 11 Old 03-17-2020, 06:43 PM
StPaul59
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Could you clarify this clamps story? I have some issues with my battery charging and I use clamps like this: could they be the problem?


These absolutely suck. You can't ever get them to stay tight..
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post #8 of 11 Old 03-17-2020, 06:46 PM
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These absolutely suck. You can't ever get them to stay tight..
What should i get then?
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post #9 of 11 Old 03-17-2020, 06:52 PM
GOLDWING
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Could you clarify this clamps story? I have some issues with my battery charging and I use clamps like this: could they be the problem?
The ones in your pic are just a nicer version of a poor design. Crushing a stranded wire cable would not be so bad if oxygen couldn't get into the connection and cause corrosion. The cable works best with a soldered connection to a terminal lug which is bolted to a marine or military style battery terminal.

GW

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post #10 of 11 Old 03-17-2020, 06:58 PM
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Originally Posted by GOLDWING View Post
The ones in your pic are just a nicer version of a poor design. Crushing a stranded wire cable would not be so bad if oxygen couldn't get into the connection and cause corrosion. The cable works best with a soldered connection to a terminal lug which is bolted to a marine or military style battery terminal.

GW
Get it now Thanks for the clarification!
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post #11 of 11 Old 03-17-2020, 10:20 PM
StPaul59
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I just bought new 4ga precut wires of appropriate length from the battery section (any auto store) and cut the silver lugs off and replaced them with copper lugs. You could keep what's on there but the copper is flatter and easier to work with. The lug going to the alt will most likely have to be trimmed with a dremel to fit. I just reused the starter wire and put a lug on It, it still starts fine.
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