Alternator Wiring

[estoltman]

I'm working through some battery drain issues with my FJ40: parasitic drain, bad alternator, and wiring.

Specific to wiring - is the white wire with the blue on it from the alternator sufficient? Should there be a heavier gauge wire? For example, should I get a dedicated heavier gauge wire from the alternator to the battery? What are the other critical connections from the alternator that require proper/heavier gauge wire?

 

[Malleus]

Do you have a '78 EWD?

 

[cruiserkev]

I have heard the white/blue wire is fine as long as the alternator puts out less than 120 amps but have no real experience to back that up. I bet others here do. That said I am running a 100 Amp GM 1 wire alternator with an Odyssey battery currently and have zero issues with the wiring itself. Unfortunately I also have the parasitic draw that I can't seem to track down. I just use a quick battery disconnect on the negative post when I know I won't be driving the 40 often. Possibly a little EMP protection as well if SHTF and it's disconnected. Never know with the fools running the world these days....
2nd thought, I'm to close to a major military base and would probably be to BBQ'd to care!

 

[estoltman]

Do you have a '78 EWD?

Sorry, not familiar with the term EWD.

 

[73FJ40]

Sorry, not familiar with the term EWD.

Neither did I.

EWD	Electrical Wiring Diagram

Regarding your wire gauge question, what are you running for an alternator? (make, model, amperage).

If a stock alternator, the wire size should be fine; I would focus on cleaning up any corrosion, particularly grounds.

 

[estoltman]

World Power Systems. Model 20-1138-11-1. Serial # A 8D1. 12V, 105A

 

[Malleus]

I asked whether or not you had the 1978 (specifically) electrical wiring diagram because every year is different and you won't be able to quickly, or properly, solve your problems without one.

Here's where you can download one: 1978 FJ40 EWD

@73FJ40 is correct: without knowing the output of your alternator, no one can help you determine if the wiring sizing is correct.

There's no guesswork involved, it's a mathematical calculation based on rejected heat load from the current carried. There are several online lists/calculators for wire size, based on current draw. This one is really simple, and its output is wire gauge, not size, which is useful if you're one of the 350,000,000 people who don't live outside the US. I would use anything from 7.5 to 15 amps (depending on the circuit you want to check; those are the limits of the fuse block) for current input (you'll need the limit for the alternator, to size for that) and 10-ft for length (it won't be longer than that and it adds a safety factor that doesn't unduly increase wire size). Leave the defaults for the other inputs.

FWIW, it matters whether the wire is stranded or solid, and copper or aluminum. It's the volume of wire and metal that determine whether it can support the current, or will fail (melt). You really need to know these concepts if you're going to be working with electricity. It's not hard, and it keeps you and your truck from frying.

 

[Malleus]

I don't have the '78 spec handy, but the '76 OEM alternator was 50A, which makes yours much heavier. The OEM wire gauge should be #8 (I have to measure that to be certain), and for 105A you'd need #2, to ensure you wouldn't melt it. You'll also need to upgrade your fusible link.

 

[estoltman]

Yep, calculator said #2. This manufacturer says they are good to 115 AMPs with their #6.

2/0 Gauge (AWG) Black and Red Pure Copper Battery Cable Wire with Lug

WindyNation is one of the nation's largest manufacturers of assembled inverter cables in the USA. Our cables are precisely cut and stripped on an automated robotic cable processing machine. Pure copper tin-coated cable lugs are then attached using a 6-ton pneumatic crimper with custom dies...

www.windynation.com

What AMP fusible link would you go to?

Since this is routed through the voltage on the dash; assume I'd leave that alone and go direct from alternator to battery w/a new fusible link?

 

[Malleus]

So, it matters how long the run is. Those battery/inverter cables are 9" long, so they dissipate heat much better than a conductor from the front of your engine to your dash. That's why I used 10' in the calculator. Also, understand that any calculation is using ideal conditions. You can be sure that you're safe using these calculations, but you may be able to get away with a little less, depending on what loads you really have.

For example, it's the same with your house; you have a 200A service, but if you add the breaker capacities, there is way more than that in the panel. No one expects you to draw the limit on every circuit all at once. The capacities are the limit, not the service load.

Your alternator's "rated" output will usually be based on 6000-rpm driven speed. It's less than that at idle (which should also be on the nameplate, or at least available from the manufacturer; you could SWAG it at 70%). So, since your current draw at the alternator is only what the load connected to it demands, you'll never see 105A. FWIW, I think my ALT lead wire is 10ga, and the calculated load for a 50A draw would require #7. So Toyota obviously knew the safe load would be far lower than the 50A capacity of the alternator.

Yes, the fusible link has to go directly from the alternator to the battery.

These questions are why I asked if you had the EWD. You need to know what is directly connected to what (the wiring diagram) and what is logically connected to what (the circuit diagram). I've never attempted to replace the OEM alternator with a 105A unit, so I'd have to sit down and figure it out, from all the loads I'd expect to be connected to the alternator, in my truck. But now that you have all the tools, you can easily do that for your specific application.

Alternately, you might ask @Coolerman; he's built more of these harnesses than anyone else. Of course, he's only going to be able to give you what would be compatible with the OEM loads. Any aftermarket accessories/upgrades (like a big alternator) add additional requirements.

 

[ToyotaMatt]

I'm working through some battery drain issues with my FJ40: parasitic drain, bad alternator, and wiring.

Specific to wiring - is the white wire with the blue on it from the alternator sufficient? Should there be a heavier gauge wire? For example, should I get a dedicated heavier gauge wire from the alternator to the battery? What are the other critical connections from the alternator that require proper/heavier gauge wire?

so ..............

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- included NEW starter LUG OEM Special service SEMS HEX NUT .....

- OEM 2005 era japan spec. positive battery terminal

- the absolute non-usa heavy duty applications BEST B+ terminals rubber soft protection cover TOYOTA has ever made in any way covers up the possible wrench that could arc to ground if that happend and does indeed occur

- in short the meets all of the original and exceeds toyota's SNOW VERSION package spec's and requirements from long ago in the 1980's ..


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[Malleus]

So now you have all the theory, here's the simple answer to your alternator question: yes, the original wiring will be fine.

Provided: there are no other non-OEM changes to the wiring harness. The reason is the draw can only be what the load demands. If there are no non-OEM loads, the original wiring from the alternator is still sized for those loads, so it's OK. The alternator can't output more than the loads require, regardless of its theoretical capacity. However, if anything new has been added, that is not necessarily true anymore.

The reason I didn't give you that first was you say you have a non-OEM alternator - I assumed that, before you gave the nameplate data, because you asked if you should change the wiring.

You also said you have a parasitic drain problem. This is unlikely if there are no non-OEM additions to the wiring harness. Not impossible, but unlikely.

So, now you need to find that problem first, using the EWD, and take into account that additional load to get the new and improved wire size (if any).

It's also worth noting that old wiring lacks the current carrying capacity of new wiring, this includes the windings in motors, so the current draw will be a little higher than what you would calculate going through the EWD and adding up the loads, maybe as much as 10%. This is due to oxidation, which reduces the volume of wire. Less wire = more heat. Current creates heat, so 15A in a #20 wire is hotter than it is in a #10 wire.

 

[estoltman]

Thank you! Technically, the only non-OEM load I have are the new LED headlights, but they probably draw less than the OEM lights. I don't even have a radio, AC, etc. I do have a big winch. It's wired directly to the battery, but I guess that could increase the load when in use, but the vehicle is always idle when using the winch.

Someone posted a pic of the cable from the battery to the starter. I do that have that one right! The factory wires from alternator and the battery side do need new connectors, cleaning up, so will do that.

I also need a new plug on the alternator. Someone commented on the Facebook I8Mud that it's NFG

 

[ToyotaMatt]

Thank you! Technically, the only non-OEM load I have are the new LED headlights, but they probably draw less than the OEM lights. I don't even have a radio, AC, etc. I do have a big winch. It's wired directly to the battery, but I guess that could increase the load when in use, but the vehicle is always idle when using the winch.

Someone posted a pic of the cable from the battery to the starter. I do that have that one right! The factory wires from alternator and the battery side do need new connectors, cleaning up, so will do that.

I also need a new plug on the alternator. Someone commented on the Facebook I8Mud that it's NFG

View attachment 3290141

ok ............?

this image above is a big

- that made in China Chinese Chairman MO grade alternator is your place to start here , and where i would personally home in on for sure ..

- the whole idea that somebody some how installed a 105A amps Rock-Auto unit like that on a 50A max possible SNOW VERSION cold-spec.
original set up , or the lower other 45A and 40A variants is deeply troubling here ?

- where did the other 55A amps that exceeded here in every way go and do when and if out of the box it actually did just that ?

- this should be jotted down for the overall matter at hand you are having here for sure ..

- i will assume it a internally regulated type that was jerry-rigged-wired to do the job of a correctly installed and wired up Genuine NipponDenso unit as toyota intended to there on that ...

- you need to come to understanding that is NOT the WAY here ...

- and if anyone suggests to you differently , you should dismiss that as incorrect FSM information
- below is a oem period correct usa-spec. 1978 2F engine externally regulated type alternator & the externally remotely mounted voltage regulator also TECH. examples of : THIS IS THE WAY

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[estoltman]

The alternator looks to be a Delco. So going to get a new plug for it tomorrow. I did replace some wiring connectors and cleaned some stuff, so will check and see how things are this week after driving. I did confirm that I do not have parasitic current drain. I didn't have a full function meter, but got an $11 today from Amazon that does everything - and I can use to replace my Klein AC live wire detector that I broke. $11. Amazing. Measure draw was 0.006 AMPs. By comparison, the interior light when on is 1.4 AMPs.

 

[45Dougal]

Your 110A alternator doesn't just make 110A. Not unless it has a load to go into, so unless you're running a power station out of your fuse box then nothing untoward will happen.
However.... when your battery is dead flat because you left your lights on, and you jumped it to get it started, your battery is now not a battery, its a dirty great load sucking everything it can get from your alternator.
Your wire is going to get warm, it's resistance will rise, and it might be OK without melting your harness for the few minutes before your battery voltage starts to recover.
It might not. I wouldn't worry about it myself. The old connections are probably bad enough to save your harness.
A 6mA drain is pretty small. One small LED or less. A dirty switch somewhere might do that - try cleaning your ignition switch inside?

 

[jcj_78FJ40]

The alternator looks to be a Delco. So going to get a new plug for it tomorrow. I did replace some wiring connectors and cleaned some stuff, so will check and see how things are this week after driving. I did confirm that I do not have parasitic current drain. I didn't have a full function meter, but got an $11 today from Amazon that does everything - and I can use to replace my Klein AC live wire detector that I broke. $11. Amazing. Measure draw was 0.006 AMPs. By comparison, the interior light when on is 1.4 AMPs.

If your alternator has two mounting ears it's probably a CS130 7973. There's a few threads on mud for this swap.

To work properly there needs to be a resistor or a lamp (4 watts, IIRC) involved.

Painless has a connector kit that includes the resistor and instructions.

Painless Wiring

Painless Performance Delco CS Style Ext. Fan GM Alternator Pigtail, Part Number 30707.

www.painlessperformance.com

When you checked for a drain, did you remove the positive battery cable and check for current between the cable and battery?

 

[estoltman]

Where does that resistor go? Assume the red wire w/the connector hooks to the center positive terminal on the alternator and the white wire connects into the Toyota harness. Like the pic I posted.

 

[estoltman]

Well curd - says the part is not available. I can get a connector and wire in a resistor.