Burnt Alternator wire after 3 hour drive

[datzenmike]

Easy fix actually. The PO probably put the wrong alternator on it and gave up and sold it. Keep the old one probably ok and you can sell or give it away to someone who needs it.

[JDMClassic]

And the "charge" light is out!!

 

[JDMClassic]

I spoke too soon I'm stuck on a road near my house..

[tr8er]

Still? Or you get her back running?

[datzenmike]

Did the lights get dimmer first?

 

Or did it stall and the battery is dead.?

[JDMClassic]

Ok so I'll recap everything from last night. After putting in the freshly charged battery the truck fired right up. Since it was the first time it started for the day I let it idle and warm up for about 15 mins.

 

As it was idling I checked on all my wiring connections and look for and smell or sighs or smoke. There were no signs of smoke or charring.

 

I felt confident enough to take her for a spin around the block just to make sure everything was good. Ran her, shift gears and turned on electrical components I.e high beam hazard lights and radio. 5 mins into the drive I noticed my lights were getting deemer and right when I pulled to a spot light I died...

 

Called my girlfriend and I jumped my truck. I had the jumper cables on for about 15mins to give me enough juice to head home. Throughout the whole time since start up the "charge" light wasn't illuminated. Made it back home and it died on my just as I parked...SMH

 

Ok so this is what's on my mind. Since I replaced my alternator why isn't my battery holding a charge?

 

The things I did:

1. Tested battery (it was good)

2. Tested alternator (it was bad)

3. Replaced section of charred wiring

4. Replaced alternator

 

Is it because I got the wrong battery?

Is it because I got wrong battery?

Is it because my setup is wrong? Hotwire from alternator doesn't lead straight to the battery

Should I have an external or internal volt reg. (1974 w/l20b swap)?

[datzenmike]

Need to re-visit this....

 

 

Never found out if you have an external voltage regulator on the inner fender. It's fist size and square metal can with rounded corners just behind the battery.

 

 

 

I think it wise to check that it's there and plugged in. What if the truck has already been converted for use with that other internal alternator???

[JDMClassic]

Doesn't look like I have one

 

[JDMClassic]

I was wondering wait are these right here? It's in my glove compartment

[datzenmike]

This is what I just picked up from pep boys... I'm trying to figure where is the ground connection is at tho

 

 

 

 

This is what you said you picked up... but you don't say if it was internal or external regulated.  Has an L on it so assume it's internal. These re-builds are cheap and often 'bad in the box'. Ask anyone.

 

Also find the old external regulator plug wiring and see if it was wired up properly for the conversion to internal regulator.

[JDMClassic]

This is what you said you picked up... but you don't say if it was internal or external regulated.  Has an L on it so assume it's internal. These re-builds are cheap and often 'bad in the box'. Ask anyone.

 

Also find the old external regulator plug wiring and see if it was wired up properly for the conversion to internal regulator.

What color is the external reg. wire? And where does it lead to. I'll try to track it down

[datzenmike]

The wiring stays the same, but... at the old external regulator plug on the fender , two pairs of wires must be joined together before you get rid of it and run on the internal regulator in the alternator.

 

wayno already posted this...

 

Yes the stock alternator for a 74 620 may have been externally regulated, but your alt. in the photo appears to be internally regulated if DanielC is correct, he mentioned in an earlier post if it had L/S on it, it was internally regulated, so someone likely changed it out.

Now if that someone did not know what they were doing and just put that alternator on the engine and expected it to work, then they have not a clue, you see if and when you change over you have to make a set of jumper wires to bypass the external regulator like I did on my 521.

This is what mine looks like on my 521, you can see the external regulator and its plug in back of my wiring mods.

[JDMClassic]

The wiring stays the same, but... at the old external regulator plug on the fender , two pairs of wires must be joined together before you get rid of it and run on the internal regulator in the alternator.wayno already posted this...

So you're telling me to join 2 wires together to convert it to an internal volt. Regulator? That's all it take for the conversation?

 

Theses wires?

[wayno]

You need a better photo of the plug.

I have a 521, so I used the 510 mod as the wires are the same colors, yours might be different, but it is basically the same, but you have to know which wires to connect to each other, as you can see in my photo above, I made jumper wires for 4 of the 6 wires in my plug.

[tr8er]

Wayno and Mike. I commend you for your patience. OP, sounds like you are taking the advice this time. You'll solve it

[wayno]

I went out today to check how I had my internally regulated alternator wired, and I found a wire loose, it must have come off when I was beefing up my custom alt. bracket I made while working on it yesterday.

So I put another end on it and plugged it back in where it was supposed to be and started the truck, I had smoke everywhere in the engine compartment, I shut it down and hurried to the front hoping there wasn't a fire.

This is what I found, all the coating on the wire is fried off.

Now I am unsure why it did this, but obviously it grounded out somewhere it was not supposed to, I made a new wire, put it in the exact same place the other wire was and I am now good to go, something happened, I am not sure what, but when you start making custom stuff, you have to be careful, otherwise your vehicle can go up in flames.

 

That said, this is how I wired my internally regulated alternator in my 521, it is a very simple setup I have.

There is a "T" plug on the back of the alternator, the top of the "T" goes to the fuse block on a keyed circuit(turn the key on, that wire has 12V), the bottom of the "T" goes to the dash light wire, the main output post goes to the positive post on the battery, and there is a main ground that goes to the body, that's it in a nut shell, it's that simple.

As I posted above, you can start a fire if your not careful.

[JDMClassic]

So I'm thinking it's this by guess. I was looking at the diagram and notices that the color of the wire are different from my truck. Mike and you point out which ones to connect to?

 

 

[datzenmike]

The '74 620 should have 6 wires to the regulator plug...

 

Black

Yellow

White/Black stripe

White

White/Blue stripe

White/Red stripe

 

Join the

 

White/Red stripe to the White/Black stripe

and

White to the Yellow

 

 

 

 

I cut the plug off the regulator and removed the unused wires and connected the correct ones. Then you just plug this into the harness plug. If you don't have the regulator tape up the unused wires.

 

 

This was also touched on page two...

 

Yes the stock alternator for a 74 620 may have been externally regulated, but your alt. in the photo appears to be internally regulated if DanielC is correct, he mentioned in an earlier post if it had L/S on it, it was internally regulated, so someone likely changed it out.

Now if that someone did not know what they were doing and just put that alternator on the engine and expected it to work, then they have not a clue, you see if and when you change over you have to make a set of jumper wires to bypass the external regulator like I did on my 521.

This is what mine looks like on my 521, you can see the external regulator and its plug in back of my wiring mods.

[JDMClassic]

The '74 620 should have 6 wires to the regulator plug...

 

Black

Yellow

White/Black stripe

White

White/Blue stripe

White/Red stripe

 

Join the

 

White/Red stripe to the White/Black stripe

and

White to the Yellow

 

 

 

 

I cut the plug off the regulator and removed the unused wires and connected the correct ones. Then you just plug this into the harness plug. If you don't have the regulator tape up the unused wires.

 

 

This was also touched on page two...

 

 

Having trouble locating. The regulator connection by what your saying about the color coded wiring list you gave me:

 

Black

Yellow

White/Black stripe

White

White/Blue stripe

White/Red stripe

 

I can't find it...

 

 

 

[wayno]

That plug is confusing, the black/yellow line wire goes to the starter, and the red/blue line wire is for the side marker lights according to the wiring diagram for a 74 Datsun 620.

The 1974 diagram also shows only 5 wires, all the rest of the years I checked had 6 wires, very confusing.

[wayno]

That white/red line wire that is cut off that plug, you do that?

[JDMClassic]

HUGE UPDATE...

 

I'm an idiot... This whole time the "S" and "L" connection was disconnected on my alternator through out this hole time causing my battery no to charge. I guess I was to excited and forgot about connecting it back..

 

So I connected it and did the poor mans alternators test by disconnecting the battery cables while the trucks was running to see if the alternator and support it's own power. And it did!

 

Went for a test drive and she did well. But the only thing that concerns me is that she dies out on stop lights. This is not all the time but 1 out 3 times she would bog out and RPM would get low. Why?

[JDMClassic]

That white/red line wire that is cut off that plug, you do that?

No didn't do that... I wonder that that leads too...

[JDMClassic]

I went out today to check how I had my internally regulated alternator wired, and I found a wire loose, it must have come off when I was beefing up my custom alt. bracket I made while working on it yesterday.

So I put another end on it and plugged it back in where it was supposed to be and started the truck, I had smoke everywhere in the engine compartment, I shut it down and hurried to the front hoping there wasn't a fire.

This is what I found, all the coating on the wire is fried off.

Now I am unsure why it did this, but obviously it grounded out somewhere it was not supposed to, I made a new wire, put it in the exact same place the other wire was and I am now good to go, something happened, I am not sure what, but when you start making custom stuff, you have to be careful, otherwise your vehicle can go up in flames.

 

That said, this is how I wired my internally regulated alternator in my 521, it is a very simple setup I have.

There is a "T" plug on the back of the alternator, the top of the "T" goes to the fuse block on a keyed circuit(turn the key on, that wire has 12V), the bottom of the "T" goes to the dash light wire, the main output post goes to the positive post on the battery, and there is a main ground that goes to the body, that's it in a nut shell, it's that simple.

As I posted above, you can start a fire if your not careful.

Thanks for the heads up! Much appreciated! I'll be sure to have some safety precautions will handling it

[wayno]

Did you charge the battery up fully before installing it in the truck?

If you did not, the alternator is working at max capacity, it don't turn easy at full charge.

I have never tried it, but I heard that it is hard to turn an alternator by hand when it is energized.

HUGE UPDATE...

I'm an idiot... This whole time the "S" and "L" connection was disconnected on my alternator through out this hole time causing my battery no to charge. I guess I was to excited and forgot about connecting it back..

So I connected it and did the poor mans alternators test by disconnecting the battery cables while the trucks was running to see if the alternator and support it's own power. And it did!

Went for a test drive and she did well. But the only thing that concerns me is that she dies out on stop lights. This is not all the time but 1 out 3 times she would bog out and RPM would get low. Why?