No Alt. light after start up but battery not topping off .. Options

[Spoke]

..
What is the battery voltage at idle? Positive terminal to chassis ground.

What is the battery voltage from positive POST to the negative POST? ..

Idleing:
D+ double checked still showing at 13.6v
Bat. + to Chassis ground = 12.49v
Bat. + to Neg. bat. post = 12.49v

Battery should be around 13.25V or higher with D+ at 13.6V

Can you measure the battery voltage and D+ with the engine at a higher RPM? If you were getting 12.5V at the battery during operation the engine should run. You might need a helper to get the engine to 2.5-3k.

[Literati914]

I did the test - jumper wire between D+/DF (with VR removed) with the engine on and got 17.25v at the battery.

[Literati914]

..
Can you measure the battery voltage and D+ with the engine at a higher RPM? If you were getting 12.5V at the battery during operation the engine should run. You might need a helper to get the engine to 2.5-3k.

With the RPM's held at 3k, I'm getting 12.91v [up from 12.49v at idle] at the battery. D+ still showing 13.69v at the same time.

[Spoke]

..
Can you measure the battery voltage and D+ with the engine at a higher RPM? If you were getting 12.5V at the battery during operation the engine should run. You might need a helper to get the engine to 2.5-3k.

With the RPM's held at 3k, I'm getting 12.91v [up from 12.49v at idle] at the battery. D+ still showing 13.69v at the same time.

Great info. Good news is it seems the alternator is keeping the battery voltage above resting voltage of 12.6V but 12.91V is low especially if D+ is reading 13.7V.

@Superhawk996
@GregAmy
it would seem that with VBAT and D+ being 0.8V different that there is a diode not functioning in the alternator. Would like to get a second opinion on this assessment.

[GregAmy]

I tend to agree that it's a diode, which is a common failure on these. The alternator is capable of raw voltage but it's not getting to the battery...

Also, connecting +12 to the DF on mine results in something like 17V. From Tom's post, "this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes." So the alternator may be a bit weak, and/or the D+ diodes are bustificated.

I've had great luck having my alternators rebuilt locally by a crusty old guy in New Hampshire that has a shop in disarray (but he knows exactly where everything is). Dallas has GOTTA have some good rebuilder shops...

[Superhawk996]

I’ve been reluctant to chime in . . . . Cause I’m just going to preach the same ol’ same ol’

There is a voltage drop (~ 0.8 - 1.1v) going on somewhere between the alternator D+ and the battery.

Ground cable between chassis and engine trans is always the first suspect on 914’s.

Next on the hit parade would be the battery cables themselves (both positive and negative).

Don’t forget the B+ wire between alternator and the starter.

So four wires / cables / ground strap portions of wiring need to be checked.

Until I had verified all those with a DMM by measuring voltage drops I wouldn’t move forward. Note: per Greg’s comments above - I don’t think a diode can be ruled out but I’d verify voltage drops in wiring first before chasing a bad diode theory.

Edit:
Note: measuring resistance of the battery cables and ground strap CANNOT be done with a DMM by measuring ohms. You have to measure voltage drop while cranking the engine to gauge whether or not the cable has excess resistance

The above pertains more to starting issues.

Since the 0.8 - 1.1v voltage drop is occurring across wiring with the engine running - voltage drops could just be measured with the engine running and ought to be apparent. .

Here’s an intro (too long . . I know . . . but necessary to understand):
https://www.fenderbender.com/running-a-shop...ircuits-part-11
Plenty of YouTubz videos on checking voltage drops too if wall of text isn’t your thing.

Will try to assist if OP wants to go down this rabbit hole.

[GregAmy]

^^^ Good points.

[Lockwodo]

If the battery voltage, measured at the terminals with battery not connected to car, really dropped from 12.77 to 12.33 overnight, then the battery discharged by 50% with no load on it and is defective. I would replace the battery before troubleshooting the charging system.

I did this again just to verify (bat. not hooked to any cables) :
Last evening the battery was charged via a manual charger to 13.02V .. today, less than 24hrs we're at 12.78V, no cables, bat. sitting in the rear trunk outdoors in the heat, to be specific - does this certainly indicate a bad battery?

12.78 volts is fully charged, so that's good. I'm guessing the 13.02 volt reading you got was immediately after the charger was removed? The battery should then settle down to 12.7 volts as it did.

[Literati914]

Still dealing with the problem of alternator not charging the battery - but Gen. dash light NOT on when the engine is running.

I'm thinking of adding a separate ground from the chassis to the alternator - where on the alternator would it be installed? I'm seeing really small diameter bolts/nuts on the back ... then there is also the big bolts at the attachment ears of the alternator body.. or, maybe just piggy-back a negative wire off the input plug at the relay board and run it down to a chassis ground?

How about a big-ish wire attached under the nut at the pivot bolt on the bottom?

[emerygt350]

I have really enjoyed my negative terminal to the fan shroud extra negative. I have brand new clean grounds in the stock locations, but that extra one between the neg and the shroud made all the difference for me.

Notice that stock coil and dizzy. So strange...

[Literati914]

I've already installed something similar - top of shroud to the neg stud on the body (battery has been relocated to the trunk). I know it’s red, but was all I had ..

[Literati914]

Also, I just found the following break in the wire casing of the brown wire at the relay plug! - think that’s enough to cause my charging issues?

[emerygt350]

Might be, however I wouldn't rely on the 50 year old body of the car too much. You may want to snake a devoted ground from the battery to the motor if the crack isn't the problem. Shouldn't be difficult if it's in the trunk.

[VaccaRabite]

It does not take much of a voltage drop to discharge your battery.
I had about a 1.5v drop between the alternator and the battery due to the ground path going through a powdercoated doghouse. They had taped off the bolt holes, but there was still enough resistance to cause an issue.

I ran a stout wire from the body of the alternator to the ground lug on the driver side of the chassis where the relay board grounds. Problem solved.

When I changed engines I kept the extra ground - easy enough to do though I admit its a belt and suspenders option while everyhting is working.

Point being, if the you have paint or corrosion around your doghouse (which is the ground path for your alternator) then you are going to have that voltage drop. It takes 10 minutes to add a ground to the alternator housing up though the tin to the ground lug behind the relay board.

Good luck!
Zach

[Literati914]

OK then, the plan is to run a wire off the lower pivot bolt of the alternator (easy to access from under the car) to a ground. The only problem is my ground over by the relay board has extra items on it already and I don't want to crowd it. I'll need to look around for another grounding spot. Any suggestions? Maybe under one of the engine bar mount bolts (IMG:style_emoticons/default/idea.gif) Anyway, I'll report back later.

[KELTY360]

Beware adding two fixes at once. The added ground is a great idea, but I’d suggest fixing that suspect wire first and testing it to know if that created the problem. Then you can add the ground as insurance.

[Superhawk996]

Also, I just found the following break in the wire casing of the brown wire at the relay plug! - think that’s enough to cause my charging issues?

Yeah!

The color of the copper underneath doesn’t look healthy. That wire (D-) brings ground up from the alternator to the voltage regulator. Without a good ground reference the voltage regulator cannot operate properly.

There is no guarantee this is your only problem. Per previous posts you also had 0.8v or more drop between D+ and the battery positive post.

Kelty360 has it right - address root cause(s) of voltage drops rather than adding grounds everywhere hoping for a fix.

If you want to measure the voltage drop in that cracked wire:

Use meter (milli-volts scale).

Engine running - voltage regulator plugged in. That alternator connected - plugged into the relay board.

Meter ground lead to alternator case. Where the lead is placed matters. Measuring to the pivot bolt or fan should will not give an accurate measurement.

Meter positive lead to the spade connector on the cracked wire, of that 3 pin alternator connector. You have to back probe that connector while it’s plugged into the relay board.

Reading should be 0.0v

Anything higher than that indicates corrosion in the wiring and a voltage drop across that wire.

[Literati914]

If you want to measure the voltage drop in that cracked wire:

Use meter (milli-volts scale).

Engine running - voltage regulator plugged in. That alternator connected - plugged into the relay board.

Meter ground lead to alternator case. Where the lead is placed matters. Measuring to the pivot bolt or fan should will not give an accurate measurement.

Meter positive lead to the spade connector on the cracked wire, of that 3 pin alternator connector. You have to back probe that connector while it’s plugged into the relay board.

Reading should be 0.0v

Anything higher than that indicates corrosion in the wiring and a voltage drop across that wire.

I went out meaning to do this test yesterday evening - immediately noticed the battery needed charging, so I slapped the charger on and just went ahead and repaired the broken wire (it had to be fixed regardless). Then it started raining, so I called it a day on the car.

-An interesting observation when charging the battery though .. with the car's battery cables still attached to the battery, I hooked up the positive side of the charger as usual, then I added the charger's neg lead to the top of the brass negative cable fitting which gave the tiniest of sparks as normal, but when I readjusted the allegator clip it would aggressively spark when touching the steel bolt of the clamp. I'd never noticed that before was kind of surprised by it. Probably normal (IMG:style_emoticons/default/confused24.gif) but would that be an indication of anything in particular? (like a parasitic draw?, bad battery ground?)