Charging system not working

[tigernut]

Car will jumpstart and run fine but will not restart on it's own after I shut her off.

I removed the horn relay for repair the other day. Must it be connected for the charging system to work?

When running, the battery shows 11.5v and the Alternator shows about 11.5v as well.

Any ideas on where to look?

Thanks.
Doug

 

[Verle]

Doug,

Depending on the year of the car, yes the horn relay in an integral part of the charging system. It is a central connection for a number of wires from the starter, generator/alternator and igintion system.

Verle

Car will jumpstart and run fine but will not restart on it's own after I shut her off.

I removed the horn relay for repair the other day. Must it be connected for the charging system to work?

When running, the battery shows 11.5v and the Alternator shows about 11.5v as well.

Any ideas on where to look?

Thanks.
Doug

 

[tigernut]

Thanks Verle. According to my wiring diagram it looks as if removing the relay would cause this and that is the last thing I can remember doing, before it started not charging.

I guess I will buy a cheap replacement while I'm rebuilding my original one and give that a shot.

Doug

 

[JohnZ]

The two screw terminals on the horn relay are on a common bus, and are the main power junction/distribution point for the whole car; if they aren't in place, nothing in the charging system will work - you need a horn relay there.

 

[tigernut]

Ok, I put the horn relay back in and jump started the car and drove for 30 minutes. When I got home, shut her down and tried to restart her, the starter wouldn't even click.

I pulled the battery and it reads about 11.7 volts, but I guess it doesn't have enough cranking power to turn the starter over.

I'm guessing the battery is shot. I'll take it to the store and have it tested.

At least my horn works now, thanks to the new relay.

Doug

 

[JohnZ]

You should see 14.0-14.5 volts at the alternator output terminal and across the battery when its running, 1500-2000 rpm, if it's charging; a typical fully-charged battery by itself (engine off) will show 12.2-12.6 volts.

 

[Tempus_Fugit]

charging system

Here are some charging system tips:

1) System (battery) voltage should be higher when it is running than when it is shut off, indicating the alternator is working.

2) A quick and dirty way to check the alternator is to see if a steel oject will "stick" to the back of the alternator, car running (be careful), this will indicate the the alternator is creating a magnetic field.

3) You can bypass the regulator and "full field" it by removing the regulator connector and jumping from red to blue, please consult shop manual first. This should cause the alternator to "sing" and charge at its max output. If alternator is ok it is probably regulator or decayed wiring.

4) Most of the time on old GM's it is the regulator. This is a mechanical device with 3 relays. The failure of any one can cause problems. Replacement units sometimes lack OE quality.

John

You should see 14.0-14.5 volts at the alternator output terminal and across the battery when its running, 1500-2000 rpm, if it's charging; a typical fully-charged battery by itself (engine off) will show 12.2-12.6 volts.

 

[wallyknoch]

Car will jumpstart and run fine but will not restart on it's own after I shut her off.

I removed the horn relay for repair the other day. Must it be connected for the charging system to work?

When running, the battery shows 11.5v and the Alternator shows about 11.5v as well.

Any ideas on where to look?

Thanks.
Doug

The alternator is not charging the battery. Nothing to do with the horn relay. One of two possibilities, a bad wire from the alternator or in the plug, or two, the alternator is dead! A correctly charging system should read 13.6-14.4 volts when running. Static battery voltage without the car running will also be over 12 volts.

 

[tigernut]

Thanks to everyone's suggestions I'm getting closer...

Took the alternator in to have it tested and it was bad. Got a new one, put it in, and it fixed somethings but still doesn't seem right.

Before the alternator install, I got no reading on my dash meter, and measured about 12.5 on the back of the alternator (across big red wire and ground).

After installing alternator, I got a negative jump on my dash meter, which jumped even more negative after I turned on the lights, and measured about 12.5 on the back of the alternator.

So I've replaced the alternator, horn relay, battery tested good and holds a recharge well, so the only thing left is the regulator, correct? (maybe why I'm still only seeing 12.5 output on the alternator? At least the dash gauge is reading something now.

I need to try John's suggestion of bypassing the regulator next.

BTW, Is removing the battery connection when running a valid test of the charging system? If I do so, the car immediately dies, which seems to tell me the charging system isn't working, as I've already found out.

Thanks to all!

 

[attret00]

I'm having the same type of problem as tigernut. My question is if you replace the regulator do you have to adjust it or is it pre-set. Also, where is a good place to buy a regulator. Tempus_Fugit says "Replacement units sometimes lack OE quality." Tigernut...when I pull my plus cable off the battery the engine keeps running.

 

[tigernut]

So I jumpered the regulator as described below and the alternator started outputting the correct 12-14volts when idle was increased.

Once I removed the jumper the system continued to charge. When I turned off the key and started again the system no longer charged.

So it appears something is wrong with my regulator as well.

That would be a horn relay, alternator and regulator that were all bad and needed replacement, but looks like I'm finally there.

Thank you to everyone for all your help.

Doug