So I finally fixed my stupid misfire I was having and now I'm
Trying to make sure all the small things are fixed before I start driving it again and I noticed my battery light is on. Checked the voltage and with the car on it stays around 18v. Any ideas on what I should check? What can cause this? Can coolant into my alternator mess it up? Sometimes when I was pulling my rad out some coolant got on it

What voltage are you getting at the alternator plug? on the post?

Bad ground. I noticed my volts at like 16-18 or something one time and my headlights were flickering brighter occasionally. Also my stereo turned off. I went and checked under the hood and found I hadn't tightened down the main ground strap for something or other and it was fine after that. Just a suggestion.

If the regulator is bad (which it could be from dumping coolant on there) it may happen. Take it out and have an auto parts store test it. If it tests fine we will go from there.

+1

Yes I'm being a post-whore today. So what!

Took it to a couple parts places and it kept failing. But they put in settings for Nissan quest since they didn't have choice for skyline. They both said the failure COULD have been due to wrong settings because it wasn't the right vehicle. Kinda sceptical and not sure what to do yet...

id say its the regulator, its not an uncommon thing to go wrong with alternators

Bumping this from the dead, trying to help a buddy out. He already replaced the alternator with 3 different ones, changed the battery, and added more grounds,voltage is still fluctuating between 16v to 11v.

Any other suggestions on what to check for? The voltage regulator is built into the alternator, is there anything in the wiring that could cause this issue?

Dumb question: Is the alternator case grounded with its own dedicated wire to the chassis?

I am having a similar issue with the charging system in my RB25 S14. Static voltage is 12.8 +/-, and drops to around 9 or 10 while cranking, however when the engine starts the voltage (read on the nistune) stays at static battery voltage (12.8) until I rev the engine once, then is stays at 15 volts. This is an unusual problem that I have never come across before, any suggestions?

^ sounds like a bad battery to me, alternator is compensating for the low voltage by providing max output.

Carl H wrote:^ sounds like a bad battery to me, alternator is compensating for the low voltage by providing max output.

Thanks Carl, I have seen you on the message boards for years, and I appreciate the response. I am new to Nico, and go by a different username on Zilvia and GTROC. Anyway, the battery was my first thought as well, but the problem persisted after a new battery was installed. The wiring harness was poorly converted a few years back, so I have since gone through it, and found some irregularities. My hopes are that this problem is related in causing the hard starting of the engine. The engine cranks excessively before barely starting, dipping in RPM, almost stalling and then eventually raise in RPM an stabilize. After that "graceful" attempt start the voltage reads what I described above, 12.8v, until I rev it once, then 15+v. Aside from starting, the engine appears to be running nice, and the Nistune data shows 15 degrees timing at idle. Any suggestions?

probe the output on the alternator...if the harness is shoddy you may be registering incorrect voltages.
make sure you have good grounds all around the motor.

Carl H wrote:probe the output on the alternator...if the harness is shoddy you may be registering incorrect voltages.
make sure you have good grounds all around the motor.

Hey Carl, the alternator output is 15 volts from the post, and I verified that the case ground is good (.2 ohms). After a bit of research, I started looking into the wires coming from the plug on the side (Sky Blue and White/Red). Even with the plug unplugged, the alternator is still putting 15.5 volts. The Sky Blue in the plug, reads static battery voltage (12.5v), and the White/Red reads .38 volts.

you using the 25 lower? sounds like the regulator isnt wired in correctly.

Carl H wrote:you using the 25 lower? sounds like the regulator isnt wired in correctly.

Carl, I wish I could tell you for sure what lower harness it is, but the wiring conversion was done "professionally" years back. If I cannot figure this out, I will likely remove the lower harness and go through it, like I did the upper harness. R33 wiring diagrams seem to be difficult to come by. There is another thread on here where another member is having the same exact problem, which you have commented on as well. I have yet to hear if he has resolved the problem yet. My suspicions are leading to the White/Red wire on the plug on the side of the alternator. This suspicion comes from this post I found.....
"the larger one (in your case aqua) in that plug goes to pos 12 v, this one i'd add a fuse. if i remember the pic i couldn't see the size fuse.

the smaller wire (white/red) goes to the change bulb wire in the gauge cluster. it is the excite wire if you don't hook this up you will need to add a resister to drop the voltage going to the alternator to less than 6 volts. if you power this wire at 6 volts your alt will charge at 15 volts. also if you just plain dont hook this wire up, your alt will not charge.

hope that helps. my experience... i wired up my whole 240 from scratch and everything works."


This is the link to other members problem, exactly the same
post6398276.html#p6398276

yeah, the w/r is the exciter/light wire and is the same colour on the s13 chassis. the other wire actually goes to the fusebox but if you trace it out on the diagram it runs to the power wires going to the battery.

i think the lt blue wire is a feedback wire for the regulator to well...regulate voltage.

Carl H wrote:yeah, the w/r is the exciter/light wire and is the same colour on the s13 chassis. the other wire actually goes to the fusebox but if you trace it out on the diagram it runs to the power wires going to the battery.

i think the lt blue wire is a feedback wire for the regulator to well...regulate voltage.

Problem Solved!!!!!!!!
While looking through the S14 FSM, and trying to remember what is different now than when it was charging normally, was.....The gauge cluster was not in the car, and as Carl noted this circuit serves a more important function than just the warning lamp.

For anyone doing an RB conversion that doesn't want to go through the trouble of maintaining the warning lamps, DON'T LEAVE OUT THIS CIRCUIT!

Thank you Carl, you were a great help! Check out a thread I have about this car
http://zilvia.net/f/tech-talk/340727-s1 ... hread.html

check the ground to the transmission under the battery tray usually is cutoff by the acid