TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > Electrical - non engine
  New Posts New Posts RSS Feed - Starts and completely dies
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

Starts and completely dies

 Post Reply Post Reply Page  <12
Author
Message
Hayes89 View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Oct/06/2017
Location: Long beach
Status: Offline
Points: 59
Post Options Post Options   Thanks (0) Thanks(0)   Quote Hayes89 Quote  Post ReplyReply Direct Link To This Post Posted: May/24/2022 at 3:51pm
Great information bud thank you I'm going to try all of that out as soon as I get back home. It sounds easy enough 😉
Back to Top
bigbad69 View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Jul/02/2007
Location: Ottawa, Ont.
Status: Offline
Points: 6614
Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2022 at 8:57am
If I read your first post correctly, the battery quickly discharges while the car is running. A shorted winding in the alternator could produce this symptom. A failed regulator wouldn't cause the battery to discharge that quickly, IMO.

A quick way to verify a failed alternator is to disconnect the alternator output wire (the heavy gauge cable) and tie it off so it doesn't contact the body of the car. With a fully charged battery, the car should run for some time. This assumes that the batteries you are using are in good condition. I would recommend getting at least one of them load tested just to be sure.
69 Javelin SST BBO 390 T10
Back to Top
Hayes89 View Drop Down
AMC Apprentice
AMC Apprentice


Joined: Oct/06/2017
Location: Long beach
Status: Offline
Points: 59
Post Options Post Options   Thanks (0) Thanks(0)   Quote Hayes89 Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2022 at 10:50am
So that would be the thick power cable coming from the starter solenoid to the alternator correct? So I have another red wire on it I think it's for the alternator bulb light
Back to Top
bigbad69 View Drop Down
Supporter of TheAMCForum
Supporter of TheAMCForum
Avatar

Joined: Jul/02/2007
Location: Ottawa, Ont.
Status: Offline
Points: 6614
Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2022 at 5:36pm
Yes, the battery + and alternator output go to the solenoid input. I don't have a wiring diagram for 72, so I don't know exactly what that third wire is for. Leave it connected as it is unlikely to be the cause of your problem.

I will quote myself:
Quote A failed regulator wouldn't cause the battery to discharge that quickly, IMO.
I suppose if the transistors in the regulator are completely fried, they could be causing a direct short to ground.

Does the battery discharge with the engine off? That is a clue.
69 Javelin SST BBO 390 T10
Back to Top
Regamble1969 View Drop Down
AMC Apprentice
AMC Apprentice
Avatar

Joined: Dec/01/2021
Location: Boise Idaho
Status: Offline
Points: 204
Post Options Post Options   Thanks (0) Thanks(0)   Quote Regamble1969 Quote  Post ReplyReply Direct Link To This Post Posted: May/25/2022 at 7:46pm
Originally posted by bigbad69 bigbad69 wrote:

I will quote myself:
Quote A failed regulator wouldn't cause the battery to discharge that quickly, IMO.
I suppose if the transistors in the regulator are completely fried, they could be causing a direct short to ground.

I pretty much agree with this. Like I said, one time 20+ years ago and I wasn't the tech on the car so my memory of that particular case is a bit foggy. And that's my understatement of the day.

What bigbad69 and I are pretty much getting at is to break it down in small diagnostic pieces.

1. Doe the battery drain in the car with the key off?
A. Yes - there is a huge drain on the non-switched side of the electrical system. This could still be the primary wire on the alternator. Disconnect it and check again.
B. No - move to next step.

2. Does the battery drain in the car with the key in the run position but not started?
A. Yes - there is a huge draw on the switched side of the electrical system. (Highly unlikely scenario but simple to test so do it anyway).
B. No - move to the next step.

3. Does the battery drain with the car running but the alternator disconnected?
A. Yes - something on the VR circuit. (Grossly and wildly unlikely... but not impossible)
B. No - the alternator likely has a shorted winding or metal contact somehow. Bad alternator.

These are the steps I would take and questions I would try to answer. Bigbad69 also mentioned getting a battery load tested, which would be a good idea if you can. It's always good to know what you're starting with.
Back to Top
 Post Reply Post Reply Page  <12
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.797 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or