ign light causing truck to not charge?

[spdcrazy]

I recently had some alt issues. i'll start by explaining my setup before the issues.

 

71 521 L20b. I was using a D21 alt, 90amp or something similar. I didn't have the correct alt plug but used weatherproof spade connections while I found the correct plug. I also had a LED bulb in the ign bulb spot on the cluster.

 

 

I  tore the car down a bit for some small projects and then reassembled for the weekend, none of the work was electrical other than a few bulb changes.

 

When I put it all back together, the alt wasn't charging, checked my wiring, all solid as it was, took out the alt and had it tested, it tested bad. I also removed the LED bulb from the ign light and forgot to replace it with an incandescent bulb. I then found a junkyard alt plug to replace my spades. installed that and put the new alt in. still no charge. next step I broke that new JY plug, therefore I had to switch it out for spades again, I then installed a new incandescent bulb in the cluster, and it works like a champ.

 

so. did I have a faulty plug? or... does the lack of a bulb in the instrument cluster for the ign light really cause the alt to not send power to the battery? 

[bilzbobaggins]

The way I understand it, it's part of the charge circuit. I don't have my manual with me though.

[spdcrazy]

electrical has never been my forte, if my thinking is correct, its absurd! that would mean if your ign light bulb was to burn out, our charging system wouldn't work, your battery would eventually die, and you'd be stuck, all due to a burned out filament.

[datsunaholic]

Almost all car manufacturers used the alt light as the field initiator.  Why Nissan labelled it "IGN" was unclear, since it's misleading.  The way it usually works is the light is grounded through the alternator, so when the alternator is charging the light has positive voltage on both sides, so it is off.  The light was sufficient to last the expected lifetime of the vehicle, but the way you were supposed to notice is when you turn on the ignition but don't start the car, all the idiot lights should come on and if they don't, that indicates a problem.

[spdcrazy]

the idea of seeing the light when in the ON position without starting it would make sense, but.... they seemed to have relied heavily on light bulb quality and longevity. not the best idea maybe? while a small problem, it just caused me to scratch my head.

 

 

I hope this thread helps someone out if they pull the bulb like I did. silly mistake.

 

Thanks!

[DanielC]

First of all, you are using a later model internally regulated alternator on your truck.  Originally, a 521 had an externally regulated alternator, and turning the ignition on caused a current to be applied to the ign (alt) and oil lights.  The voltage regulator also got a second source of power , and the 1971 external regulator used this current to supply the field windings in the alternator.  One of the relays in the voltage regulator grounded the ignition light, causing it to come on.

 

The D21 alternator is internally regulated.  Depending on how the alternator internal regulator is wired, it can not require any current from a charge light, it might require a small amount of current, or a large amount of current.  If your alternator required a fair amount of current, a LED may simply not pass  enough current for the alternator to start charging.

[spdcrazy]

honestly you lost me with most of that. however, with the LED light bulb in it worked. couldn't tell ya if there was any differences in voltage output, if any. however with the LED it was always dimly lit. Read somewhere that was because of the difference in resistance, that is when I took it out and didn't replace it right away. now with the "factory" bulb in, all is well.

 

if i'm understanding anything you saying, the factory ER setup used the VR to tell it to charge, and the usual IR swap uses the dummy light circuit being the VR is bypassed?

 

Sorry, i'm not real savvy with electrical .

[datzenmike]

Use the proper bulb. It draws more current than an LED. Alternator needs this.

[DanielC]

You are understanding correctly.  On a stock ER setup, the voltage applied directly to the voltage regulator is connected to the alternator field coil.  This can be as much as two to five amps of current.

 

An internal regulated alternator uses the charge light to supply the current directly to the field coil.   A stock incandescent charge light is about 1.7 watts, and needs about 150 milliamps to light up.   A LED of the same brightness is about 15 to 20 milliamps.   A milliamp is one thousandths of an amp.  Once an internally regulated alternator starts to charge, it no longer uses the charge light current to work, it then supplies its own current, from the current it is generating.

[kelowg]

Another option would be add volt meter gauge. Replace bulb with proper size resistor(300ohm.1/2 watt i think). Resistor likely to never wear out and gauge is always there to give status

[thisismatt]

My charge bulb burned out....

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

said no one. Ever.

[spdcrazy]

no idea if this could possibly be related, however, I ran into more electrical problems. had the new alt in, and the incandescent bulb installed, all was well, 14.4 volts when charging, ran well for a couple days, then I go out yesterday morning and the battery was dead, I go to jump it with my handy jump box, and after starting it and letting it run for 30 or so sec, I see sparks and smoke, the wire from the output to the starter lug was on fire, melting and shorting on the frame. so I disconnect the jump box, and let it cool. cut away the wire so it won't short on the frame, jump the truck knowing I won't have an alt and drive it home. I then replace the melted wire, and as I hook up the now charged battery, I see the alt almost immediately turn glowing red hot, smoke boils out and I quickly disconnect the battery. I obviously have a short somewhere, but how! it was working just fine 24hrs before this, and I haven't touched it! only think is the oil leak I have from the fuel pump ( think the pivot pin is the problem area) could the oil leak have caused the short? or do I have some other electrical voodoo going on?

[spdcrazy]

ohh, and when I replaced the melted wire which was prob a 14g. I took a page from danielC's book and used a 10g. maybe this is why the alt turned red instead of the wire melting? either way I have a major problem.

[banzai510(hainz)]

try another alternator.

 

 

I would thinka  fuse somewhere your POP

 

 

NO on the oil on alternator. shit I have water on alt gas on alt and still works

[DanielC]

The diodes in the alternator are possibly bad.

Disconnect the negative battery terminal.

Disconnect the two small wires from the alternator.

Disconnect the positive wire from the alternator.

Reconnect the negative battery terminal.

Connect the wire from a test light to the POSITIVE battery terminal.

Touch the probe from the test light to the big positive terminal on the alternator.

Light on, alternator bad.

[thisismatt]

Did you ever say if you've bypassed the external regulator or not?

[spdcrazy]

I don't know if I said it, but yes it is bypassed!

[spdcrazy]

I'll test this tomorrow and report back! I didn't get to spend any time with it today, Mother in law was in town. back to datsuns and beer tomorrow

[That4doorKiD]

AHHHH!! I have LEDs in my gauge cluster and swapped IR alternators from a 78 200sx(60amper) and 78 620. Followed the wiring diagram on DQ...so I jumped four connections using two wires and four male spades. Thought I had connected it wrong and was double checking a thousand times last night, drove me crazy so I gave up for the night hahaha. Plus my ignition lights constantly stays on when the car is turned on and key is on ign. No wonder my alternator doesn't charge.

 

Hopefully this is the problem when I wake up tomorrow morning to try it

[That4doorKiD]

Thanks!!

[That4doorKiD]

AHHHH!! I have LEDs in my gauge cluster and swapped IR alternators from a 78 200sx(60amper) and 78 620. Followed the wiring diagram on DQ...so I jumped four connections using two wires and four male spades. Thought I had connected it wrong and was double checking a thousand times last night, drove me crazy so I gave up for the night hahaha. Plus my ignition lights constantly stays on when the car is turned on and key is on ign. No wonder my alternator doesn't charge.

 

Hopefully this is the problem when I wake up tomorrow morning to try it

[spdcrazy]

yep, it was my problem. among other unrelated but coincidental things.

 

short version, keep a regular incandescent buld in the charge light.