Want 2nd opinion on electrical

[ferox]

Today is a special day. I am doing the 100 amp GM alt swap on my '81 Hatch (which is requiring more fab than anticipated but that's another story). I am replacing all the wiring between alt and battery, removing the external voltage regulator and in-line fusible links, and installing a (post-'81) Fusible Link Box at the junction. It is this connection that I want confirmation on. It looks pretty straightforward. Pictured is the external voltage regulator and attendant schwag next to the J-box that is to be installed.

 

 

Here's my plan:

 

The black wire with the white stripe on the old set-up will go in the first position on the f. link box.

 

The large white power wire from the alt. will be up-sized to 6 gauge and go in the middle position in the f. link box.

 

At the bottom of the picture (on the old set-up) you can see three wires factory crimped and soldered to the large white power wire...two small white wires (one coming from the voltage regulator) and a blue one. I am planning on soldering those three wires to a piece of 8 gauge and installing it in the third position in the j-box. WILL THAT WORK? IS IT BAD? Thoughts or condemnations? Also, I am using 6 gauge wire between the j-box and battery. Seems like it will work, but since it's electrical and I am pumpin' more juice I would like a second (or many more) opinion(s).

 

Sorry about the picture size, I cropped it and resized it and it still came out huge.

[GeneralDisorder]

Seems like it will work, but since it's electrical and I am pumpin' more juice I would like a second (or many more) opinion(s).

 

Well - you aren't pumping more juice unless you are drawing more juice than the factory accesories. An alternator capable of 100 amps (and that's not an idle figure BTW - it's more like 30 amps at idle, and 100 amps at 4,000 RPM. But those numbers are what it CAN put out. Not what it IS putting out. That depends on what you hook up to it.

 

An 86 Maxima alt is 90 amp, bolts right up, and cost about the same... I would return that huge GM thing if it were me. I know folks that have had bad luck with those beasts.

 

Just using the fusible link box from an 82 to 84 EA81 will net you NO ability to run anything other than the stock accesories. The links are not sized for anything above their stock draw. You will need extra fusible link(s) for more accesories, and you'll need another fuse panel to feed with the new link. EA82 fusible link boxes have 4 posistions .

 

You will need to properly size the links you use to the circuits they feed in your 81. Check the wireing diagrams and see what the circuits look like and what Subaru used for the original links. It very easily could be different than the links in the box you have.

 

As for the wireing - why would you reattach the white wire going to the external VR? You are removing the external VR, so you should be able to leave that disconnected.

 

In addition to the 6 gauge wire for the alternator output, you will also need a junction sensor wire going to the fusible link junction so the internal VR can regulate the voltage at the junction. The third wire off the alt goes to the charge indicator light in the gauge cluster (probably one of the wires from the external VR plug.

 

GD

[ferox]

Alright, so thanks for your response and let me make sure I understand you in line item fashion.

 

Well - you aren't pumping more juice unless you are drawing more juice than the factory accesories. An alternator capable of 100 amps (and that's not an idle figure BTW - it's more like 30 amps at idle, and 100 amps at 4,000 RPM. But those numbers are what it CAN put out. Not what it IS putting out. That depends on what you hook up to it.

 

I'm just running stock electrical draw right now, but that will change in the future, and I figured if I hooked it up wrong I could end up causing an unforeseen draw that could be dangerous.

 

An 86 Maxima alt is 90 amp, bolts right up, and cost about the same... I would return that huge GM thing if it were me. I know folks that have had bad luck with those beasts.

 

The Nissan Alt. as it turns out would have probably been an easier install, but I was going by the GM alt. write-up which was easier than mine turned out to be. That, however, couldn't be accurately determined until I had ground down the ears and at that point I was committed. So we'll see how it goes.

 

Just using the fusible link box from an 82 to 84 EA81 will net you NO ability to run anything other than the stock accesories. The links are not sized for anything above their stock draw. You will need extra fusible link(s) for more accesories, and you'll need another fuse panel to feed with the new link. EA82 fusible link boxes have 4 posistions

 

The fusible link box install was really just to clean things up and make sure I had a good junction. The fusible links dangling from the battery has always kind of bothered me. They could be augmented to not just hang there, but then why not just put them in a stock j-box. I will definitely get some EA82 boxes for future additions. Eventually I am going to do a bunch of relay by-passes and have accessories.

 

You will need to properly size the links you use to the circuits they feed in your 81. Check the wireing diagrams and see what the circuits look like and what Subaru used for the original links. It very easily could be different than the links in the box you have.

 

The wiring diagram in the Haynes shows red fusible links. I don't have the FSM yet, but it sounds like Qman is going to help me out with that. My girlfriend's 84 wag has red, green, green.

 

As for the wireing - why would you reattach the white wire going to the external VR? You are removing the external VR, so you should be able to leave that disconnected.

 

I wasn't sure if the white wire from the ext volt. reg. was the remote voltage sensor connection. It's a yellow wire entering the voltage regulator and a white one leaving it. If I didn't reconnect the three circuits from the volt. reg. wouldn't the open circuits cause some problems? Doesn't the remote voltage sensor connection go through the voltage regulator?

 

In addition to the 6 gauge wire for the alternator output, you will also need a junction sensor wire going to the fusible link junction so the internal VR can regulate the voltage at the junction. The third wire off the alt goes to the charge indicator light in the gauge cluster (probably one of the wires from the external VR plug.

 

Are you saying I should connect straight from the stator plug to the j-box?

 

I am not trying to get fancy here, but I think my alt. and voltage regulator were on their way out, so it seemed like a good time to switch to a more powerful internally regulated set-up.

 

I'm still not sure if you are saying that this set-up is dangerous, reckless, go, no-go. I've actually already installed everything, I just have to go get a different sized v-belt. My concerns are safety first and the integrity of the car. I really needed to do something about the charging system. I think I compromised my alt while welding a little exhaust hole (yes I used the ground clamp), I disconnected everything from the alt but didn't remove it from the car. Lesson learned, it has been weak and getting worse since then.

[GeneralDisorder]

It's not a bad swap, you just have to get the external vs. internal wiring right.

 

Remove the external VR. Any circuit that goes through it should be rewired to work without it. That may include your fuel pump but I would have to check the FSM to know exactly.

 

Run a new sensor wire - forget the one in the VR because the white wire from the VR plug WAS the sensor wire - all of it. The external VR contains the sensor - not the alt. You need a good sized wire for the sensor, so run a new one from the junction to the new internally regulated alt.

 

GD

[ferox]

Thanks for the sensor wire tip. I was following the write-up by RenaissanceMan on the ext. vr removal and int. vr alt install, but that didn't include the j-box mod and a 100 amp alt. I was concerned about the fuel pump being affected, but he says it works after the VR extraction. So if I understand correctly the little white wire from the old ext. VR can be disconnected. I am just going to connect new the sensor wire (#12?) and the other white wire (currently in the 3rd j-box slot) to the original position spliced on the power wire before the j-box and it will be analogous to the original connection with a proper sensor connection and protected f. links instead of the old danglers. I am happy to say that I got the ridiculously large unit to fit where the stock alt. used to sit without fitment issues with the air cleaner. Looks good, we'll see how it works. Thanks again, I really appreciate it.

[GeneralDisorder]

His swap instructions are for installing only a very slightly more powerful alternator. For the GM 100 amp, the sense wire should be larger, and should be located at the point where you want the voltage to be regulated after any line losses due to wireing. It's typical to see around a 1 to 1.5 volt drop between the output terminal of the alternator and the junction. The sense wire will allow the alternator to put out higher than 14.5 volts so that the voltage at the junction remains at 14.5.

 

The other wire is the charge indicator/feild excitation wire. It's wired to switched battery positive, in series with a bulb that indicates failure of the alternator. There *should* be no flow through the excitation circuit unless the alternator fails to create acceptable DC current. It will flicker and flash (along with other indicators) if the rectifier goes, and it will come on steady if the brushes or the regulator die. Bearing failure will usually take out the rectifier diodes or the VR as it often causes the brushes to skip and arc - voltage spikes will kill the VR quick-like.

 

GD

[ferox]

Thanks GD. I'll make sure the sensor wire is at least as large as the pigtail at the stator plug. Thanks for the indicator lamp explaination too. I actually did a lot of reading on this before touching anything. There is a particularily helpful discussion you and RavenTK had with a certain Trikerbob I think, that had good explanations and good links. I read all of that, but it's great to hear it again, really. (ANYONE READING THIS THAT IS THINKING ABOUT THE SWAP WITHOUT FULL UNDERSTANDING OF THE SYSTEM SHOULD READ THE AFOREMENTIONED DISCUSSION...I will try to post the link in here later, I'm still learning how to use this site) I feel confident that I will not burn up my car with this upgrade now. Thanks again GD, helpful as always.

[ferox]

I'm not sure how link a thread to a post yet, but to get to the discussion I mentioned in the previous post you do an advanced search for:

 

alternator+wiring+question

 

Titles only

 

Sort by: Relevancy

 

It's the first thread that comes up.