How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Mark Your Own Question

Mark
Mark, 22 Year Factory trained technician
Category: Jeep
Satisfied Customers: 11266
Experience:  Jeep factory training........25 years in the industry.
12104952
Type Your Jeep Question Here...
Mark is online now
A new question is answered every 9 seconds

I have a 1990 Jeep Wrangler YJ. The altenater is not charging

Customer Question

I have a 1990 Jeep Wrangler YJ. The altenater is not charging the battery. I just had the battery tested it is fine no dead cells. The alternater is putting out 12.7amps.When i start it and disconnect the battery it dies immediatly.This problem has been ongoing and i have a Hanes repair manual.I just cant understand wiring diagram.The voltage regulator is in the alternater and is ok.Is ther anything else in the components that can be changed or checked? Battery terminals have been changed also.
Submitted: 4 years ago.
Category: Jeep
Expert:  Mark replied 4 years ago.

Do you have a volt meter to check a couple of things?

Customer: replied 4 years ago.
yes sir a digital
Expert:  Mark replied 4 years ago.

Ok, The large battery wire at the alternator.....can you tell me the voltage reading on that wire.

 

Also, the 2 wire plug that goes into the alternator, can you tell me the voltage on each of those wires with the key in the on position.

Customer: replied 4 years ago.
Ok Mark lets see if i can explain. At alt plug red large wire is 15.8 the small gray or black wire at plug is 14.7 to 14.8 the bolt on back of alt is 15.8 .Now my battery cable has 2 leads large red goes to starter and small red goes to a terminal block on fire wall and is bolted at top of terminal. The 2 leads from alternator 1 from plug and the one from the bolt on back of alternator are twist tied together with a black changable 2 prong fuseable link and then bolts to that top bolt on the terminal on the fire wall. This concerns me that both alternator leads tie together this way. With jeep running meter test on battery is 12.2
Customer: replied 4 years ago.
Mark im sorry i did test to wrong. With key in on position at plug red large wire is (O.OO) the gray or black small wire is 8.9
Expert:  Mark replied 4 years ago.

Here is a pic of the charging circuit.

 

The brown wire at the alternator is only supposed to have 2 to 4 volts on it because they are using a resistor wire to lower the voltage.........unless this has been bypassed?? if you have 8.9, then we'll go with that.

 

Now if you do not have 12 volts on the other wire. then according to the diagram, you probably have a bad fusible link up near the starter relay

 

graphic

 

Also be sure and test all your fuses. There should be one or two fuses in the underhood fuse box that relate to the alternator.

 

 

Customer: replied 4 years ago.
Mark i do not locate a under hood fuse box or like a power ditribution box so im not sure where those would be located is it possible the starter relay is bad even thought the jeep will start when i charge the battery.
Expert:  Mark replied 4 years ago.

Ok, the power distribution box was brought into play in late 90 or early 91 so maybe you don't have that. The fusible link I'm referring to is a section of wire that is designed to burn or melt and according to the diagram it is between the alternator and starter relay on that wire with zero volts.

 

No, I'm not expecting to find a bad starter relay here.

Mark, 22 Year Factory trained technician
Category: Jeep
Satisfied Customers: 11266
Experience: Jeep factory training........25 years in the industry.
Mark and 9 other Jeep Specialists are ready to help you
Customer: replied 4 years ago.
Ok i will try these things and thanks for the diagram.
Expert:  Mark replied 4 years ago.
You're welcome.

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • Thank you so much for your answer. My initial estimate was $325; I got it done for $100 - part and labor. Lynn B. Ormond Beach, FL
< Last | Next >
  • Thank you so much for your answer. My initial estimate was $325; I got it done for $100 - part and labor. Lynn B. Ormond Beach, FL
  • I was skeptical at first but thought I'd give it a try. I was pleasantly surprised. Your site actually is a quality service that I would recommend to others in a heartbeat. Stan Sayre, PA
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
 
 
 

Meet The Experts:

 
 
 
  • Mark

    22 Year Factory trained technician

    Satisfied Customers:

    2548
    Jeep factory training........25 years in the industry.
< Last | Next >
  • http://ww2.justanswer.com/uploads/MO/MoparCertified/2012-6-7_4142_mechanic.64x64.jpg Mark's Avatar

    Mark

    22 Year Factory trained technician

    Satisfied Customers:

    2548
    Jeep factory training........25 years in the industry.
  • http://ww2.justanswer.com/uploads/jeep10000/2008-9-18_222938_192601.jpg Chris's Avatar

    Chris

    Shop Foreman

    Satisfied Customers:

    2265
    Jeep and ASE Certified Master Tech
  • http://ww2.justanswer.com/uploads/ke4ich/2009-08-12_212931_DSC02211.JPG moparfl's Avatar

    moparfl

    ASE Certified Technician

    Satisfied Customers:

    1128
    ASE Master Tech Chrysler Dodge Jeep Master Tech
  • http://ww2.justanswer.com/uploads/nvltgo/2010-10-18_211525_youranswers.jpg Dave's Avatar

    Dave

    Jeep Master Tech

    Satisfied Customers:

    1120
    Chrysler Triple Master, ASE master Tech AA degree in Auto.
  • http://ww2.justanswer.com/uploads/tsmodie/2009-6-10_144056_tim.jpg Tim Mohr's Avatar

    Tim Mohr

    ASE MASTER TECH

    Satisfied Customers:

    805
    30 YRS EXPERIENCE, FOREIGN AND DOMESTIC, GAS AND DEISEL
  • http://ww2.justanswer.com/uploads/CD/CDJMastertech/2012-6-9_201455_JustAnswerProfilelarger.64x64.JPG CDJMasterTech's Avatar

    CDJMasterTech

    Jeep MasterTech

    Satisfied Customers:

    576
    Factory trained and certified Jeep Master Technician, ASE Master Technician
  • http://ww2.justanswer.com/uploads/jeepmopar76/2009-3-18_2204_63998760.jpg jeepmopar76's Avatar

    jeepmopar76

    Jeep/Chrysler Triple Master Tech

    Satisfied Customers:

    572
    32yr ASE Master Tech, 9yr Chrysler Master Tech, 19 yr Jeep Dealership service including AMC/Eagle