Alternator Wire?

[p11g20t]

1978 200sx - so my alternator died on me (or so i thought) - i was driving, lights dimmed finally went off, when i pushed brakes in it would bog the engine down and kill it. the engine would run just fine as long as nothing was powered. if i turned lights or brakes on, it would kill the engine. i grabbed an oldddd used alty at a junkyard for free, put it in, didnt change anything. i figured it was dead. i had it tested and he said it was fine. then he tested it again and said it was bad (knechts).

so i bought a new alty, put it in, it seemed fine for an hour or two, then the same things happened. now it should be a 3 wire alternator, although i have this extra one too. whats this one do and where does it go? what do you guys think the issue might be?

 

and yes i know the white plug has to be plugged in as well lol, i just undid it for access.

 

 

 

none of my gauges ever worked, but they lit up. the battery light was always on, and the gauge didnt read anything, but neither did anything else, and it ran okay for quite a while, so i figure its not related.

[Cuts metal like mad]

Dont be surprised if the "NEW" alternator was already bad or on its way out when you took it out of the box. Its pretty common, especially on the ones with a "life time warranty".

[izzo]

my 720 4x4 had something similar, it was connected to the bat on the alternator tho. not sure

[datzenmike]

That's a capacitor for noise suppression for the radio. Will run without. The motor cutting with lights on or any draw is what happens when the battery is low. Alt may not be charging (could be bad as izzo said even if new) loose wires, the + wire goes through a fusible link to get to the battery I think. It could be bad or loose bat terminals.

[p11g20t]

with the belt on will it automatically put out power when running with no wires connected?

or is there a remote wire that turns the alternator on?

i noticed when it was running before the low battery light was always on (because the gauges dont work) but now its not on at all. doesnt that connect to the alternator as the remote wire? could this be my problem?

[datzenmike]

Turn you key to ON (without starting) does the charge or low battery light come on??? If it does then the bulb is fine. If it does not light it could be burned out, very rare. The charge light has to work or the alt will not charge.

[p11g20t]

no it doesnt!

[p11g20t]

The bulb is not burned out but it does not come on. Now what? Any way to bypass this?

[Cuts metal like mad]

The bulb is not burned out but it does not come on. Now what? Any way to bypass this?

 

Based on a visual inspection? or did you put power to it? continuity test?

 

I havent had an alternator tested in a long time, but last time I did, it was at shucks. Their machine did not do a 'load' test and the alt passed. My friend had a load tester and it failed. So much for shucks testing machine.

[p11g20t]

I used a voltmeter on an ohms setting and it showed the same with the probes touching as when connected to either side of the bulb

[p11g20t]

I Also replaced the bulb with another one I had lying around and nada

[LenRobertson]

A couple of electrical gremlins I've had on my '79 SX, which may or may not relate to your problem. When I first got mine running, the gauges would work sometimes/sometimes not. That turned out to be a bad fusible link wire coming off the pos. battery cable. Fusible links are the two short wires with plug ins on each end that go between the pos battery post and the wiring harness. Mine showed no sign on the insulation around the wire that anything was wrong (they are designed to burn out if there is a major short circuit), but it must have had a break inside that sometimes would pass current, but not all the time. I replaced it with a wrecking lot fusible link, and it has been fine. I can't remember what the charging system was doing at this time. I suspect it wasn't charging, but I fixed the fusible before the battery ran down.

 

Second weird problem - after a few years, most of the gauges and turn signals quit working. That was caused by a bad relay, from the wiring diagram, I believe it is what is called the ignition relay. On the '79, it is located above the passenger side kick panel. But I think I looked there on an older SX at Pull n Save and didn't find it there, so it may be in a different location on '77 and '78 (if those years even use that relay). I made a jumper wire to replace the relay as a test. I've never got around to buying the relay. I reach over and plug in the jumper every time I run the car. If it is left plugged in for over a day, it drains the battery. If I forget to plug it in, gauges and turn signals are dead, and the charge light comes on. I've never put a meter on to see if it is actually not charging with the jumper unplugged, but I suspect it isn't charging. You can do a continuity test on the relay. There are two pairs of wires going to it. You should have continuity through each pair. Be careful if you do a jumper wire in place of the relay. One wire of each pair is a power wire. If you jump those two powers to each other, the result is a dead short and melting insulation (yeah, I know from experience).

 

Finally, test across all your fuses in the fuse box with a test light to be certain they are actually passing current. Don't just trust a visual inspection of the fuses. I had some trouble with tarnish on the fuse holder metal clips until I cleaned them well.

 

Len

[p11g20t]

As for now, which wire is the exciter wire at the alternator?

I can just run a wire from the battery to a small light then to that wire and it should turn the alternator on right?

 

Thank you, that gave me some stuff to check!

[Cuts metal like mad]

The S terminal on the alt is what turns it on if I remember correctly.

[LenRobertson]

First the disclaimer - I'm not especially good at wiring. So I'm just looking at the wiring diagram in the '79 shop manual and following it. I hope the wire colors are the same between the '79 diagram and your year ('78 isn't it?). Four wires going to the alt. Black wire goes to the stud designated E in the diagram (don't know if it is marked on the alt). This seems to be the ground wire. White wire goes to stud B. This wire comes from battery pos post, through a fusible link (wire is white going into link). Another white wire going into two-prong plug on alt is just teed off the other white wire ( and hence goes back to batt. pos.) It goes to S terminal on alt. So I think the wire you are looking for is the white-with-black-stripe wire going into the plug (the L terminal on alt). This WB wire traces back to the ignition relay (turned on by key switch), charge warning lamp, and auto choke relay. There is also a 10 amp fuse between the ignition relay and the charge lamp. It looks to me like a bad fuse, ignition relay, or choke relay could kill power to the L alt terminal (WB wire). If you unplug the two prong plug, the white wire into the plug should be live all the time, the WB should be live with the key on. I hope someone with more knowledge of alts will wade in here if I'm way wrong on this. If my wife were home, she could do a pic of the wiring diagram and send it to you. But she isn't here, so you'll have to make do with my probably confusing description.

 

Any progress on your carb problem?

 

Len

[Cuts metal like mad]

Ahhh, correction. S is direct battery, and L is LAMP. Duh. :D

[deadmonkey]

Looking at the first post:

http://community.ratsun.net/topic/25594-alternator-wire/page__view__findpost__p__368189

Pictres shows the regular wires not connected (the two that are perpendicular to eachoter and accept a plug of the same shape)

 

I assume it is just unplugged for the picture?

If not that HAS to be plugged in that is the circuit the charge bulb goes through.

Also, with a '78 they switch from externaly regulated to internally regulated so the alternator HAS to be internally regulated or it won't work.

NOTE: This was the case with my '78 620, not sure if this applies to the 200sx

 

But like datsumike says... make sure to test the bulb with that wire plugged in.

[p11g20t]

Ok so I used a spare light and jumped between the two wires in the plug on the alternator. Dash light lit right up as well as the jumper light, suddenly got 14.6 volts, drove her about 60 miles, charged great. If a fuse or anything was blown, the dash light wouldn't have lit right up would it?

The dash wire at the alty wasn't getting 12v when ignition was on. Now clearly it is with it jumped of course

[p11g20t]

trying to use some deductive reasoning.... :rolleyes:

 

there should be a square. bat - ignition - d light - alty

if the battery isnt charged it should act like the ground side of the light and it turns on. if the ignition is off the circuit isnt complete - light off. my light is off with the car on, but there is no charge from the alternator still.

i jumped a wire (with a light) from the battery positive to the plug on the alty, and both dash and jumper lights are on now when the car is on. when the car is off, the jumper light stays on, dash light does not. so somehow the jumper light is being grounded with the car off. plausible?

how is the jumper staying on then, does it seem like theres a short somewhere causing them to stay on? maybe the ignition is between the d light and the alty, so when the ignition is off the alty is grounded, and the d light side is cut off from the circuit therefore is grounded (from a short) on the battery side, and cut off on the ignition side. then the ignition is turned on and we have the jumper from the battery to alty - to the ignition, to the d light, grounded at the short, thus turning them both on.

still plausible? my head hurts.

[datzenmike]

One side of the charge lamp goes to the alt twin plug, the White/Red wire, the other through the ign. switch to the fuse box and to the battery.

 

Key off the circuit is open no light.

Key on (no start) power from the battery flows through the lamp to the alt and it lights.

Key on engine running and alt charging. 12 volts on both sides of lamp, no flow or power, lamp goes out.

[p11g20t]

so how does this line up with my outcome? one light, then both?

[Cuts metal like mad]

so how does this line up with my outcome? one light, then both?

 

The dash light runs through the IGN side of the fuse box. The 'test' light you are using is direct to the battery. Deduction concludes that there is a problem between your fuse box and the dash light. However, at this point, who knows!

[p11g20t]

Woww I twisted all the fuses and boom, whole dash and alty works fine.

[p11g20t]

Plus the backup buzzer works, and the dash brake light. And the stereo. Who knows what else! This is fantastic lol

[Cuts metal like mad]

Congrats, another datsun saved from the crusher.