Dead Battery!

J

jbrubaker001

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Greetings Everyone,

I am a new owner of a 74 CS and have an issue w/ the battery charging. I do have several projects but overall the car is in great shape and I basically just want to drive the car for a while and just enjoy the new experience. Unfortunately, the battery will not keep a charge. The red "L" light indicator stays on when the car is turned off (at least until the battery dies). I can jump the car but the battery will not stay charged.

I've checked the connections and they appear to be in order. My first thought is that I need to replace the alternator. I will get this tested but wanted to see if there is any obvious things that I should review prior to taking the car in.

Thanks in advance for any/all help,

John
 
IIRC on '72's..You can test continuity of the Blu (exciter) lead to the regulator between terminals 2 (goes to fuse block #6) and 8 (to the reg) of the computer test plug. The blu lead goes to the Dash red light then to dimmer switch and to fuse #6...so dimmer switch could be a problem a lose back plate can disengage contacts.

What is Bat voltage Off and On and Running over 1800 rpm? could be dead cell??
Jon
 
Ok - completed limited tests.
1) Battery - 13.6v on, 12.9 off
2) Alt - red to ground - 13.9v

The terminology used below is a little confusing to me and the instructions per the link below are the same. The battery/system was dead when I started this process. I plugged up the charger, got the car running and ran my tests. When I hooked up the charger the regulator started buzzing pretty good but stopped after about 10 seconds.

I do have a question, even though the system won't hold the charge - what is draining the system of power while the car is turned off. I have made sure there are no lights on and the only thing I can think of draining the power would be the clock.

Thoughts?
 
The clock draw in negligible. The only unexpected current could be if either the interior lights in the trunk or glove box stay on. You can remove those bulbs or remove fuses to be sure. You can also measure the OFF current at the battery of course.
 
Unexpected electrical draw

Since the warning light comes on and you're charging there is a fault with the regulator. There is a diode called an excitor which turns off the light. It has some other switching function with the other diodes which could be causing a draw. Disconnect the red wire and see if the battery drains.

As Arde says- to check a draw- pull the fuses one at a time while measuring the battery to narrow down what else could be causing a draw.

The lighting circuit isn't generally fused though. So besides the switch make sure your turn signal isn't on and you didn't notice. ( Yep, I did it and even my new Porsche does it too but it beeps to hell and back.) In fact, go through everything on the dash and console to make sure everything is off since it's sometimes not so obvious especially to a new owner.
 
Your voltage seems reasonable at test time. So the ALT may be OK, regulators/rectifiers can have intermittent issues at the transistors/diodes; but they should not cause a drain.

You may have some drain/short in one of the circuits/busses (just like my MGB). To diagnose you will most likely need to do some exclusion type tests. You will need to hook a test light bulb (12v) at the Bat in series with ground (IIRC, but it could be at the Positive post). You will need to locate it such that you can see it from the cabin where you will do the tests. Once you have the light in series you take the fuses out one by one to see which one removed causes the light to go out. Then you look for the devices and connections on that circuit to find the problem.

I hope someone more articulate than I can post the method...I am reciting from a memory years ago. The method is common, we just need to verify it.
Jon
 
I'm going to complete the remaining tests today but thought of one other potential culprit? What about the radio? Do you have to actually turn the radio off regardless or is it automicatically when the key is in the "off" position?
 
I think radios can be wired either way as they were dealer or owner installed. Mine is off with the switch in the OFF position. But if the radio stays on you would notice...

The other obvious test is to disconnect the battery after recharge and see if it holds the charge while disconnected.
 
Fused

The radio is fused and operated by the ignition switch position. Seperate amps are usually run straight off the bat, but switched from the head unit ( radio on.) if by chance you have one.

The buzzing- that part contains the voltage cut out ( regulates charge load). If those contacts stay closed it will drain the battery back through the alternator overnight. It should be possible to see the drain through the wiring at that location when testing with the key off.

Older cars regulators were much larger and you could actually adjust this setting , clean the contacts, and see the problem. Bosch and the Dark Lord Lucas.
 
Make 100% sure the battery is good? I Had a bad battery that cause similar issues!

Guys you might be over thinking the problem!

Before I call an emergency meeting on myself I always start at simple solutions first!

1. Make sure the battery is good. (it might have a shorted cell). I had a weak battery that cause similar issues. The car started in the morning then sometimes after driving it would not start... Thought had to be charging system issue... Turned out to be a defective battery that was only 3 months old...

2. Simple test of the alternator/charging system... With the car running turn the headlights on and rev the engine to see if the lights get brighter...

If the battery is junk then you can stop there if the car is not charging then you can start to diagnose the problem with advise included herein...
 
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Ok - here are the latest tests I've run so far and the red "L" is still lighting up when car is "off"

1) Battery is not an issue - made sure it was full charge last night, disconnected from everything and checked again this morning - read 12.3v this AM. Also, had another good battery available and hooked this up w/ no changes.
2) Hooked up ohm meter in series w/ ground of battery and positive battery cable disconnected from bat - reads .93 ohms - in order, disconnected fuses. Only change was on #5 (hazard lamp, glove box light, trunk light) from .93 to 1.03 ohms. Verified all lights were out when car in off position.
3) Hooked voltmeter to term #2 and #8 on the test plug (ignition off) - reads 10.28v - don't know what this means. Disconnected the red wire to the alt - this went to 0.0v. Also, w/ iginition off, tested volts on the battery w/ the red wire to alt connected and disconnected and noted about a drop of 1v.

This is what I have for now - thoughts?

Again, thanks for everyone's help.
 
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Hi John,
I'm new to E9s' so you'll have to excuse my ignorance. You mention the red'L' light is staying on with the ignition off! What is this light?

When checking for current draw in the workshop we would use an amp meter in series and would normally expect to see approximately 0.05 amps with no excess current draw present.

Have you monitored the tell tale light with the alternator or other electrical devices disconnected?

Hope this is of some help.

Richard
 
Battery woes

I suggest you check out the regulator. On the e3/e9 they are not internal to the alternator.
If a diode starts to fail then a small back emf can discharge the battery.
A failing regulator can also fry a battery in fairly quick which will destroy its ability to hold a charge.
Also because of the way the system is designed, with a full electrical load, ie all headlights blower etc, the alternator warning light can glow very faintly (you will only notice in the dark with the internal instrument light turned down.)
 
Ok, I've ordered the regulator. Once it's in I will let everyone know what happened. I did note that the black lead wire going to the current reg looks pretty fried and there were several exposed areas before I cleaned up w/ some electrical tape. I will most likely replace this wire at some point but will worry about this once I've curred this issue. Any additional thoughts would be greatly appreciated.
 
I would replace that wire while you're at it, it is a common issue and can cause shorts against the other two wires or to ground near the battery tray.
 
Alright - picked up my OE Bosche regulator from my local NAPA today, installed and.....red "L" light is still on when key is in off position. I will check the drain tomorrow and see where I stand in the mornning.

For no good reason, I started tweaking around the alternator. I unplugged the three prong connector from the alt and red "L" light goes out. Does this tell us anything?
 
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