91 XJ Battery Charging/Possible fuse box issues - JeepForum.com
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post #1 of 10 Old 02-02-2020, 05:49 PM Thread Starter
dirtbagjeeper
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1991 XJ Cherokee 
 
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91 XJ Battery Charging/Possible fuse box issues

(Yes! I've searched the forum for an answer to this mystifying issue!)

My 91 XJ started with an issue about 2 weeks ago of only running for 10 min or so then shutting off and refusing to start. Had already replaced crank sensor, o2 sensor, map sensor, throttle position sensor, manifold temp sensor. Cleaned all grounds. Cleaned fuse box with electrical cleaner.

Also has:
New fuel pump/filter
New starter
New battery

Installed new alternator and installed an external voltage regulator. We still can't get the battery to charge while running. Have disconnected radio and aftermarket temperature gauge just to rule out the odd parasitic draw. The highest the voltage will read on the battery while running is 11.80. When turned off battery goes back to 12.6.

Then we finally stumbled upon the possibility of the two alternator fuses being blown, tried to replace both since both were blown (I believe they are fuse 8 & 16). (All other fuses and relays are good )

The two alternator fuses instantly pop/blow when inserting them. Out of curiosity tested where fuse is inserted, and those two fuse blocks are both pushing out 12v. Had never heard about that being normal so went to my husband's 94 XJ and tested those alternator fuse blocks, and of course saw that they weren't pushing out anything so my 91 XJ is acting abnormally in that department.

I'm kind of at a loss to where to go from here. On the plus side the innards of my XJ will be at least half new when this is all said and done with...

I am so appreciative of any suggestions at this point.

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post #2 of 10 Old 02-03-2020, 04:56 AM
JWELK
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Welcome to the forum: A 91 and a 94 and never had to join. Amazing!!!
Never had a '91 so I haven't a book. If both fuses clear when inserted, you have a major short circuit somewhere after the fuse. Could even be the fuseholder(s) themselves. Pacific coast has great, easy to use manuals. They are downloadable. Go to the section on fuse locations to start. This will give you the wire colors and what circuits they supply. It is obvious it is in the charging circuit, as that is what is not working. Could be as simple as the wrong regulator. Some regulators are grounded and vary the positive current, others require the alternator field to be energized and vary the ground. Mine is the latter, don't know on yours. But that would most definitely clear both fuses instantly.
Put a charger on the battery, you don't want to add a new battery to the cost.
Let us know
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post #3 of 10 Old 02-03-2020, 07:36 AM
jtec
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GOOD NEWS = wiring is often easy for me.
BAD NEWS = this is the mickey mouse wiring diagram era.

There are 4 wires on ALT? could you tell us the colors... mainly the charging (big) wire
RED or BLK/WHT

Some of the 1991's have constant 12v on the alt circuits

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 10 Old 02-03-2020, 10:26 PM
rep-tile
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There is a fusible link inside the positive lead that goes from the alternator to the positive of the battery. Make sure there is continuity.

04 WJ 4.0 - Avital 4103, DB-ALL
91 XJ 4.0 - Avital 4103, Stage-2 aFe intake system, BBK high flow Throttle Body, Jones Exhaust A3518M-5
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post #5 of 10 Old 02-03-2020, 11:38 PM
2oldjeeps
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fuses blow? battery voltage goes thru fuses to alt. alt most be bad or wired wrong.
also if not charging its because the fuses are open!!
alt is the problem...


oh also, you put in an external regulator? that can also be the problem.
always look at the last place someone worked. go backwards...

99wj,143,000 miles
00xj,177,000 miles
10hummer3,74,000 miles
98xj,130,000 miles
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post #6 of 10 Old 02-04-2020, 04:39 AM
JWELK
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Quote:
Originally Posted by rep-tile View Post
There is a fusible link inside the positive lead that goes from the alternator to the positive of the battery. Make sure there is continuity.
While she may or may not have an original OEM fused cable, she has a major short circuit in the charging circuit causing two fuses to clear instantaneously.
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post #7 of 10 Old 02-04-2020, 12:59 PM Thread Starter
dirtbagjeeper
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Okay, disconnected external voltage regulator and tried to put fuses in... Instantly blown again. Oh and now the ignition fuse has blown as well.

This thing has gremlins living in it. I don't believe alternator is wired wrong, maybe it is a brand new bad one?

I'm at the point of accepting defeat and calling a mobile mechanic 🤑
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post #8 of 10 Old 02-04-2020, 03:26 PM
2oldjeeps
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repeat..
fuses blow? battery voltage goes thru fuses to alt. alt most be bad or wired wrong.
note, most =must !!

are you seeing?

99wj,143,000 miles
00xj,177,000 miles
10hummer3,74,000 miles
98xj,130,000 miles
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post #9 of 10 Old 02-04-2020, 10:53 PM
rep-tile
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Here we go. Black/gray wire is shorting to ground. Likely frayed wire.
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04 WJ 4.0 - Avital 4103, DB-ALL
91 XJ 4.0 - Avital 4103, Stage-2 aFe intake system, BBK high flow Throttle Body, Jones Exhaust A3518M-5
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post #10 of 10 Old 02-05-2020, 11:40 AM Thread Starter
dirtbagjeeper
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Thank you!!! Will check this tonight.
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