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hbradbur 06-18-2012 02:01 PM

Battery not charging 0n 1987 Jeep Wrangler
Help Please! I have replaced the battery and then replaced the Alternator with a 78 amp output. I still cannot get the battery to charge and cannot make out heads/tails with the wiring diagrams in the manual. I understand from reading that the voltage regulator is internal to the alternator. When running I do read 14 V as output from the alternator.

This falls within the parameters specified in the manual.

This jeep is a 6 cylinder, no AC nothing fancy. I have installed new battery cables, and negative has good connection to engine. I do not have a seperate ground wire from (-) of battery to body (never had one).

This problem started about 6 months ago. I cannot determine if this year/model has a computer. It does have some relays next to the battery, but I cannot find any information on what they do. Fuses under the dash all tested good.

Is there a main fuse between the Alternator and Battery??

Any help would be appreciated - thanks in advance.

camarozz 06-18-2012 04:25 PM

Not really sure, I have not had problems with the charging system with mine, but I can look when I get home and let you know what I see.

In the mean time, you mention 14v at the alternator which is good; but you didnt mention if you tested it at the battery. I suspect it should be there at the battery, they are typically directly connected.

Do me a favor and tell us exactly what is happening, and what lead you to suspect there was an alternator problem. I havent had too many troubles with my jeeps before, but I have had other rigs that were really sensitive to some minor corrosion on terminals at the battery and the starter solenoid that made the system act like the battery was dead. That may be your problem, especially if your battery seems "wet" on top. That battery acid is horrible on connections and if that ends up being the case, there are some really good treatments to help keep the corrosion down; from those red and green felt buttons, to coatings. I bought some VERY expensive goo to coat my terminals and have not had a corrosion issue since. Small bottle and brush was $20, but that little bit goes a long way (about 12 batteries so far and I still have 99% of the bottle left). I will see if I can get the name and post it for you.

Oh, and yes... it does have a computer. Its up under the dash above the air box and behind the glove box (ish).

jeepjeep2011 06-20-2012 01:40 PM

Can you jump it off? I have an '89 that has an issue with starting. The battery seems dead. If it does start, when I stop at a red light or stop sign it will die. no spit / no sputter. I go to start back up and will not even turn over. After time checking under the hood, it will start.

hbradbur 06-26-2012 12:51 PM

Sorry for the delay. I had to travel to the jeep location. Still tracing wires through the harness.

What I found so far. There are two hot leads from the Alternator (Red wires). One comes off the back post (bolt on) of the Delco Alternator, the other comes from the top (clip on) of the atlernator. The top is a two wire connector (large red wire 10ga, one black/green 14 ga wire). Traced these two wires back to the starter solenoid. They are factory spliced together with a single wire connected to the battery side of the soloied (left had side). ALso found on the left side (battery side) of the starter solenoid are two green wires. Each green wire is facotry spliced to a "Y" connector - so green comes from solenoid they Y's to 2 red wres. These wire (so far) are running back to through the firewall.

Alternator wires were frayed and I replaced the "Y" connector but have not started the jeep yet because battery is dead.

Battery reads 10 volts right now, and have not test voltage with jeep running. I will attempt to jump start it this morning and see if the voltage is 12+ or better from alternator.

Other than that, I have today to try to fix before I leave town to go back home.


camarozz 06-26-2012 12:57 PM

Good luck, but if you can try and charge the battery as slowly as you can for a day or so. This will help top off the charge and hopefully limit the damage done to the cells.

hbradbur 06-26-2012 01:35 PM

Battery can be charged and then it will start fine, but if driving at night or with wipers on, once battery is drained it will die. If runnning without any other electrical devices, it will run longer but always shows discharge. Again, once battery runs down, it will die.

Heading over to sons house now to check into it more. Found some info online that if the Alt. does not see 12 volts at the battery, the alternator sensor will not put out a charge. There are three wires at the alternator - 2 red - 12 or 10 gauge and a black/green. I'm going to trace out where the black/green runs too.

hbradbur 06-27-2012 12:30 PM

Might be fixed? I cut off the factory end on the alternator side and put on a new crimp on lug, cutoff the facotry splice on the starter solanoid side and re-spliced the existing (2) red 10 ga wires from the alternator with a new tail (10 ga red), put a new crimped end on it.

Cleaned all connectors at the solanoid, both ends of the battery cables. Slow charged the battery - it was holding 12 volts.

Once connected, jeep started (as always) - But this time - while running the volt/ohm meter shows the battery at 14/15 volts. Turn on all lights - and it holds at 14/15 volts.

Before all this cleaning/retermination - volts at battery while running was 7/8 volts.

I think the problem is fixed, but my son let me know after coffee last night that in the past, if the jeep sat for 48 hours it would not start (dead battery). I will check it on Friday before returning to Utah. The differenct is it now shows the battery is being charged when running where in the past it was always in a discharge state.

I will reply to this reply on friday if all is well.

camarozz 06-27-2012 09:19 PM

Sounds great, although I would be a little concerned with 15 volts with you saying the battery has a full charge. A typical "good" charge voltage should be between 13.8 and 14.3v, otherwise it is over charging and can also be a problem. I probably wouldnt worry if it was as high as 14.5 though.

Although Im not familiar with a higher output alternator and maybe that is a part of that so you can run some extra accessories. But if you are turning all your lights on and keeping 14/15 volts then that is definitely good that it does not seem to be loading it down.

Even though, Im not sure if you can do anything either if it is trying to charge at 15 volts, unless there is something wrong with that alternator.

Desert Scorpion 07-25-2012 02:50 AM

ok i'm having a very similar problem with my 89' jeep sahara. the battery stopped getting a charge from the alternator so i had the alt. tested and it passed then replaced the connections going to the alt. worked fine and was showing 14v going to the battery. 4 days later same problem happens i popped the hood looked at and touched the wires and there is no heat coming from the wires and no corrosion on the connections. then i put my hand on the alt. and it was so hot i had to back off immediately could this be a problem with the alt.? or a wire short out? i feel like the wires would have been hot if it was a short out. maybe im wrong. any help would be much appreciated.

shotgun123 07-25-2012 01:10 PM

I am also having troubles, battery not keeping charge, some things are my fault like not turning the switch in off position........Well, anyway Alt and battery tested, good, battery needed a boost.........I replaced all cables( hot /ground) leading to the whatever it was on the firewall, while inspecting that piece I noticed another hot going to the starter, it is there surpose to be two very small, 10 gauge wire on the two screw coming out of what ever is on the firewall? if so there is only one and where do I find the other little wire that goes on the other? And what is that piece called?

hbradbur 07-26-2012 09:37 AM

Update to battery not charging. It's going on the fouth week and all is well with the charging. The conole guage is always showing 14+ volts output even when lights and radio are on. A new high output Alternator had been installed and the NAPA battery was only a few months old.

I found in another post that the alternator will not attempt to charge the battery "if" the battery voltage is less than 10 volts (My son had confirmed that the console gauge always showed 8 volts). The second red wire (10 gauge) that connects to the side of the alternator (in plastic clip) is a senor wire to tell the alternator to "charge" when it senses the battery dropping below 12 volts. Apparently, if the battery gets too low, it never tells the alternator to charge. I always assumed a alternator just "outputs" regardless. Anyway - based on that post I did the following stuff.

I removed the red wire (10 gauge) from the back of the alternator and replaced the connector with a new crimp-on lug. I removed the wire harness (clip with two wires) from the side of the alternator and removed the grime, tarnish from these clips and re-inserted them into the plastic clip and re-connected them to the alternaor. One of these wires is also a large gauge red wire (10 gauge).
I removed the factory harness cover and traced both the red wires from the alternator back to the firewall. Both of these wires are spliced (factory) together near the solonoid and then terminate on the battery side of the solonoid. The factory spice was removed. I cut back both wires, cleaned the ends and spliced a new tail (10 gauge) red wire to both (Y connection) and connected to the battery side of the solonoid. Only one wire runs from the solonoid to the starter. The small green wire connections were cleaned and reconnected to the small posts of the solonoid.

The battery was removed and slow charged/verified it was 12 Volts and re-installed. All battery connections were cleaned. The battery ground cable to the engine block was cleaned/re-connected as well.

A (10 gauge) ground was run from the battery negative and connected to the firewall. Paint was removed from firewall to ensure a good connection.

Fan belt was verified it was tight.

I checked the red wire (10 gauge) on the side of the alternator with the engine off and verified it read 12 volts (wire connects to solonoid/battery side).

Once started, the gauge on the dash showed the system was charging at 14+ volts.

I did have issues with taillights, turnsignals and dash lights not working. :-) I tried to walk my son through the process (on the phone) of pulling fuses to isolate which circuit might be causing a short or drawing current when the jeep was turned off. I had asked him to remove fuses one at a time while looking for a drain on the battery. I guess I should have also told him that the fuses needed to go back into the same spot! Anyway, once I put the fuses where they belonged everything worked just fine.

The old jeep is humming along and I'm hopping it will last another 25 years!

I hope the above information helps others out. It was getting very frustrating trying to decode the electrical drawings from the Haynes Manual. Tearing into the wire harness was much easier for me. I'm going to assume it was a combination of bad electrical connections and the battery having drained down to a point that the alternator sensor did not see a battery at the other end of the wire?

camarozz 07-26-2012 12:06 PM

Very nice, glad it worked out.

Thats the thing about older vehicles, as the electrical ages all sorts of corrosion and breaks happen. I have a connection at my trailer plug that corroded through that I had to track down to fix.

Rjones3023 09-16-2013 11:37 AM

Hbradbur, I just wanted to say thank you for your write-up you posted a year ago. I had the same problem and followed your post and corrected my charging issue!


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