Exhausting all options before new alternator

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66NCVW
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Exhausting all options before new alternator

Post by 66NCVW » Sat Jan 21, 2017 3:49 am

Hey all,

I have a 1966 bug that's been converted to 12v. It was already converted when I bought the car, and from the best I can tell its wired per this diagram with an AL82N alternator in place of the generator. In other words my alternator has two red power wires coming off of B+ as shown in this diagram. One wire goes to the starter. The other wire goes up to the front. I do not have a wire from B+ on my alternator to the battery directly. The starter has a wire that goes from the battery to the starter so it gets it's 12V there? Anyways I want to know if this is correct as I'm having some issues. My voltage is only what the battery has. The voltage at 2k RPM is whatever the battery has. It does not jump to 13.4+ Volts. Also my alternator light is on dimly, then gets brighter as you rev the engine. Before I buy and replace the alternator, I wanted to make sure this wiring is correct for a 12V alternator in place of the generator. Also my ground strap from the transaxle to the pan is in super rough shape and I'll be replacing that tomorrow.

EDIT: Sorry for rambling on, but its almost 4AM here and this thing is kicking my ass. :?


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Re: Exhausting all options before new alternator

Post by sideshow » Sat Jan 21, 2017 11:02 am

I bypass the dash lamp when I suspect a bad alternator. With the engine running and good battery voltage at the post fake that excite circuit.

All you need in the common 12 test lamp to touch between spade and B+ (clamp to B+ and pointy end to male .250)

Nothing more fancy than http://www.harborfreight.com/circuit-tester-30779.html , if you are really cheap the tail lamp/plate light will also work.
Yeah some may call it overkill, but you can't have too much overkill.

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66NCVW
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Re: Exhausting all options before new alternator

Post by 66NCVW » Sat Jan 21, 2017 1:31 pm

OK! Heres the latest. Jumped the exciter plug to 12V, and boom we have charging, alt light goes out. I also switched warning lights without jumping the exciter plug and the other light does the same thing rev the engine and gets brighter. Jump the exciter and boom all goes well again. So could I just run a new wire from the warning lamp to the exciter plug, or do you think the issue is in the lamp itself? Thanks for the help, I should've tried that before ( the simplest solution seemed like it couldn't be the problem? ) lol :mrgreen:

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Re: Exhausting all options before new alternator

Post by Marc » Sat Jan 21, 2017 2:37 pm

The warning light will illuminate whenever there's sufficient difference in potential across it...in EITHER DIRECTION (it's only a light bulb, it has no brains).
It compares what it sees from the D+ post on the alternator to what's getting to it from the alternator/battery, via the connections at the fusebox and/or lighting switch and through the contacts of the ignition switch.
If there's resistance in the longer path, it's to be expected that the warning lamp will glow with increased intensity as the alternator output increases...add to the load by turning on the lights/wipers and it'll be even more pronounced.

Check all connections in the current path (also look for "crispy" wires with melted insulation - those usually are where high resistance will be found) starting with that transaxle-mount ground strap that you already know is bad.

As for the "dual" B+ wires, that's a legit configuration (provided all the connections are good, and the one from alternator B+ to battery cable is of adequate size). On OE alternator-equipped cars the factory did it differently, bonding the battery positive to the wire going from alternator B+ to the front of the car, but electrically there's no difference assuming no significant resistance in the wiring.

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Re: Exhausting all options before new alternator

Post by 66NCVW » Mon Jan 23, 2017 4:22 pm

Ok, this is more than frustrating at this point. I ran a new wire from the Alt light to the alternator. Fired it up no charge. Jump it from the b+ post to the Alt light terminal on the alternator and boom 13.4+ volts. Also the alt light stays on still. I've cleaned all the contacts and ran a new wire? I can't believe something this simple is beating the crap out of me. :x 8)

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Re: Exhausting all options before new alternator

Post by Marc » Mon Jan 23, 2017 4:49 pm

Your approach defies logic. The problem's not on the D+ path, it's on the other side of the warning lamp - the basic integrity of the car's primary electrical system...something's causing the reference voltage on the ignition-switch side of the warning lamp to be too low, so the light comes on when it's receiving higher voltage from the D+ terminal when the alternator's putting out.

Make sure that the battery cables and ground straps are all in good shape with clean/tight connections at both ends.

Assuming that the ground path is good, you could confirm the diagnosis by attaching a temporary jumper cable from the battery positive post up to Term 30 of the ignition switch - that would bypass any problems which might exist in the wiring up to that point and the warning light should act normally.

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Re: Exhausting all options before new alternator

Post by 66NCVW » Tue Jan 24, 2017 1:49 pm

Ok, I went over the entire system last night. Here is what I've come up with. I cleaned up the connectors, checked all the grounds again. I've replaced the ground strap from the trans to frame. I checked the ground path by doing as you stated and jumping the term 30 to the battery. No change in the actions of the alternator light. I can't seem to find a draw on the system with the car off, but when I attach and detach my ground it sparks a little? :?: The alternator Like clockwork will start charging as soon as I jump the d+ and b+, though. I also switched the bulb around to rule that out as well. I did find out that one headlight wire was in the wrong spot though haha. :mrgreen: Could this be an issue with the connection from the regulator to the output in the alternator? Thanks in advance for your help!

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Re: Exhausting all options before new alternator

Post by Marc » Tue Jan 24, 2017 2:20 pm

You've definitely got something drawing current if you see a spark when detaching/attaching a battery cable - often it's just the dome light, make sure it's turned off. A radio with clock and/or station presets also draws a tiny current when off, although I wouldn't expect it to be enough to cause a visible spark. When tracing a current draw it's easiest to insert a light bulb between the battery cable and the battery post (easier to see it glow than to see a tiny spark).

I'm still not convinced that your alternator is faulty but without being there to look first-hand I'm not going to stake my life on it. The jumper wire from B+ to Term 30 should have bypassed any resistance in the harness connections; if it made no difference my working theory is blown up. You did also clean/tighten the connection where the negative battery cable bolts to the pan, right?

Is your new AL82 a Brazilian-made model? Those have the regulator buried inside where you can't access it without removing & disassembling the alternator (on the German-built ones it was integral with the brushholder).

It's possible that the field brushes are not making good contact with the slip rings - that could explain why it's taking a full 12V "shot" to get the field flashed. It's not particularly difficult to remove the brushholder and inspect the brushes/springs & slip rings, but that might be considered "tampering" which could void your warranty.

On a `66, power from the alternator/battery first goes to the lighting switch, then to the fusepanel and finally to the ignition switch - the light switch and fusepanel have extra terminals so they can be used as junction points but they aren't active components in the current path to the ignition switch. When the headlamps are on the voltage is drawn down (due to resistance in the wiring to the light switch) but it should still be enough to flash the alternator through the warning lamp filament...if the warning lamp has been replaced with an LED a diode has to be installed across it.

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Re: Exhausting all options before new alternator

Post by 66NCVW » Tue Jan 24, 2017 3:45 pm

I ran the jumper from Battery positive side up to TERM30 on the ignition switch. Would it make a difference to do it from the B+ terminal on the alternator to the ignition switch ?

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Re: Exhausting all options before new alternator

Post by Marc » Tue Jan 24, 2017 4:10 pm

66NCVW wrote:I ran the jumper from Battery positive side up to TERM30 on the ignition switch. Would it make a difference to do it from the B+ terminal on the alternator to the ignition switch ?
Certainly couldn't hurt in the spirit of symptom elaboration, if you have different results it would help zero in on any problem with the wiring.

To be worth doing, the jumper wire should be as heavy-gauge as you can manage...I was thinking of using a jumper cable for most of the run, extended if necessary to reach the ignition switch with a piece of at least 12GA.

Remember, this only affects the positive side of the circuit so to be meaningful the grounds must be good - you say that's been addressed.

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Re: Exhausting all options before new alternator

Post by 66NCVW » Tue Jan 24, 2017 5:47 pm

Yep grounds have been addressed. They've been replaced, cleaned, and I added one. I have a new symptom. I decided to try bypassing the light, and exciting the alternator off a switched 12V source. Fired it up and it ran fine and charged. Well when I turned off the ignition the car wouldn't shut off until I disconnected the wire from the 12V source. I could turn the key to the off position and it kept right on running. Somewhere power is back feeding. I have two posts on my starter with wires. One goes to the battery post from the starter. The other has two wires. One goes to the alternator, the other one runs up to the front of the car to the panel. If these are both on the same post on the starter could that cause this? I didn't have this particular issue when I got the car, and I haven't changed the way it's wired up.

Thank you

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Re: Exhausting all options before new alternator

Post by Marc » Tue Jan 24, 2017 6:54 pm

66NCVW wrote:...Somewhere power is back feeding...
Yep, it would do that. In stock configuation without your "excitation switch" the resistance of the warning lamp filament is enough to reduce the voltage backfeeding to the coil from the alternator, so the engine will die even though the alternator's still making voltage at D+.

Some "high-performance" electronic ignition systems have a similar problem because they will still make a spark even with reduced supply voltage; on those it's necessary to add a blocking diode to prevent the D+ power backfeeding through the warning lamp getting to the coil...but that's not a solution in this case if you want to have a functional warning lamp.

If you leave the 12V applied to D+ after the alternator kicks in, you're bypassing the warning lamp so it will never come on, even if you toss a fanbelt. If you're planning to keep this "fix" in place, use a spring-return-to-off toggle or a pushbutton.

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Re: Exhausting all options before new alternator

Post by 66NCVW » Tue Jan 24, 2017 9:08 pm

Im Efi with megasquirt, so if I put a diode on the switch 12v wire to the alternator "exciter" that should stop the back feeding ? I want a functional warning lamp but I need it to charge in the meantime until I figure out what exactly is going on with my electrical system :cry:

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Re: Exhausting all options before new alternator

Post by Marc » Tue Jan 24, 2017 11:07 pm

EFI alone shouldn't make any difference; it's the ignition design that matters - with a stock-based setup using points or a Pertronix-type pickup run-on isn't a problem, where you run into this issue is with an MSD or similar setup which has a coil capable of producing a usable spark even when supplied with a low input voltage.
Another option would be to put a "kill" switch in the wire going back to the coil that you could use to open the circuit when shutting off. That'd also slow down most car thieves.

I'm thinking that what you're proposing would compromise the function of the warning light (since it'd still be bypassed in one direction of current flow by the diode), but you could try it and see. Sorry, but I'm three hours into cocktail hour and a little fuzzy ;)
Using a momentary switch for your "exciter" wire instead would have no downside that I can think of...

I've alluded to this before, but just to be doubly sure - your charging system warning lamp is an incandescent bulb and NOT an LED, right?

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Re: Exhausting all options before new alternator

Post by 66NCVW » Wed Jan 25, 2017 11:33 am

Correct it is NOT LED. It's a regular white incandescent. I tried switching it with the bulb from the oil warning light as well and it didn't make a difference. I haven't totally ruled out the bulb though, b/c I haven't seen if the bulb would act normally while jumping 12V to the alternator.

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