Ok, so to cut to the chase....I have a 2nd new battery battery new alternator. First alternator lasted 2 months. Ending up stalling out a few times. Then the last time, I lost power completely and couldn't go over 3-5mph. Had all the signs, battery light/brake light combo on the dash and no power. Got towed and checked. Turns out my alternator wasn't charging. So I got a new alternator. Mechanic/friend at shop said it was giving the warning lights again. He cleaned on of the main grounds really well and drove it around a bit. No problems with the warning lights on the dash anymore. I took the car and parked it for the day. I had another car I need to use at that time.

The next day I took my car home. Everything was fine, until I got close to my house. (I live about 12 miles away) The battery and and brake light started to flicker. I was worried about the same problem going on. I parked my car in the driveway.

Worried the next day, I drove to work. Lights would flicker sometimes, but usually at lower speeds. Couldn't tell for sure. Made it to work fine for the 12 mile drive. Today I looked for all the grounds I could find and cleaning all bolts, surfaces, with a wire brush for 4 hours or so. Might have missed a few, but I did get the big one under the radiator fluid overfill.

Started it up in the shop and the battery light and brake light flicker. If I rev the engine a bit the warning lights go away. I do a battery and alternator test. Batter is reading normal. Turn the engine on and I should get increase in voltage right? Actually it goes does down. This would indicate that the alternator is not charging. Not sure what to think.

I decide to take a chance and drive home. No problems whatsoever performance wise. One thing that was definitive though was if I was at a low speed(13 mph or less), slowing down and at a low speed, or coasting in neutral...the brake/battery warning light would flicker. Once I started giving it some gas and driving at normal speeds it would go away. If I was stopped, brake/battery warning light would stay on solid.

So is my alternator charging if the warnning lights go away? I made it home fine and don't feel any performance changes. What would cause something like this? Thanks in advance.

 

Shot in the dark. Have you checked all your power and ground wires to make sure they are tight and have a good connection?

 

I spent 4 hours removing, cleaning, and tightening grounds. I haven't done anything with power wires though. I've tightened the connectioins to the battery, but that's about it. Maybe I should just upgrade the wiring on the alternator anyway. I just don't know how difficult it is to do with all the wires wrapped in that plastic tubing and running into a connector. Does anyone know or can explain how to change the wires for the alternator? Can I run it straight to the battery? Thanks.

 

Have the exact same issue. Will keep monitoring .

 

I'm having a similar issue, slightly different symptoms, but close enough. Was this ever resolved? I see the last post by the OP is 1/12/2013. 6 years and no update?

 

One other question. How is the brake light associated with the charging circuit? What causes it to illuminate when it shouldn't even be part of the circuit?

 

The brake light is not associated with the charging circuit, however a common problem people have is the cap on the brake switch snaps off and the brake lights are on ALL THE TIME, this drains the battery.

Take your car down to a battery shop and have them load bank test the battery, this is not done with a voltage test meter, they will wheel out a small cart, hook up to the battery with the engine OFF, the cart has a large electric heating element in it to put a load on the battery and they watch for voltage drop while it's under load.

Next test the alternator, this is easily done with a digital multimeter, you should have about 14.5 volts while the engine is running.

I strongly recommend disconnecting both battery terminals, the bolted fittings on the fusible link, the alternator primary battery wire, and the rest of the grounding jumpers (battery to chassis, chassis below the coolant reservoir to right side of timing chain cover) and clean everything thoroughly with a wire brush, apply electrical anti-oxidation grease like ILSCO DE-OX or equivalent, then bolt everything back together.

Loose or corroded connections will definitely cause issues that are commonly mistaken for other problems. Thoroughly inspect the length of the alternator primary battery wire for damage/melting/lumpy spots/bulges/etc. Replace as needed.

 

I was pretty certain that is the case, however when my battery light is on the brake light is on as well. The OP of this thread describes the same issue like it's a common thing. It doesn't make sense.

As for the bank load test on the battery I don't know if that has been done. I've been to a dealer and two other shops that have been unable to diagnose this issue. I'll make sure to get this test done as I have been suspecting the battery.

 

Id scan it for any OBD2 codes first.

 

Check the belt for proper tension and make sure it is not contaminated with any liquids, such as oil or antifreeze.

 

Update for 6 January 2020

First off, thanks to tjrob2000 for sending me a private message for an update.



Upfront summary----

So, what ended up being the problem was the alternator was not charging properly. I went through 2 faulty alternators not charging properly and finally getting one that seemed to work intermittently only to have an overcharging issue in the end. I believe it was the voltage regulator inside of the alternator. The alternators I purchased were off of an ebay seller from a UK vendor that sold refurbished alternators. Back in 2013, I lived in the UK and getting stuff from the US was not as easy so I went with the options I had. I’m back stateside now so that is not a problem any longer. Finally, the fix came from purchasing a used OEM alternator for a Skyline 350GT, which is basically the same car in UK if you can find one. I’m still using the same alternator as of 2020 and now have close to 250K miles on my G.

Diagnosis---

Figuring out that is was an overcharging issue was difficult as there where no OBD2 codes being thrown and symptoms did not register when monitored by my local garage when performing battery and alternator tests. The problems started happening when I drove and it happened when revs started to increase. The way I was able to see the overcharge was because I have a DashDaq XL installed in the cubby hole of my dash that is always connected to the OBD2 port. I was monitoring my battery and noticed spikes above 16v that occurred when revving the engine during driving. I don’t know if this issue could be easily diagnosed for someone that does not have digital monitoring capabilities while he or she is driving.

Other concerns---

One thing that may have contributed to my alternator and battery issues were underlying ground issues. Before this time, I had my engine rebuilt for boost and when the engine was reinstalled it is possible the ground attachments were not reinstalled properly. I followed guides to cleaning my grounds, but even after doing so I always felt there was an underlying ground issue with car. The reason I say that is because of a prior breakdown where a guy from AA in the UK (like AAA in the US) came out to help me with my car and installed a new ground wire so my car could start again. Furthermore, when I came back to the US in 2018 I ended up purchasing a SxExCx grounding kit from Sean. Having a 6MT, I did not expect much, but I truly feel the grounding kit has improved the overall performance of my vehicle. It starts quicker and just feels more responsive overall. Now, I may have noticed more of difference because I probably had real grounding issues so the improvement for me with the grounding kit was noticeable even with a manual transmission compared to owners that only see a difference in automatic transmission Gs.

Regarding the symptoms with my brake light is one I cannot say is uniform for all owners. My US spec G35 was slightly modified with lighting for use on UK roads. I have orange leds for turn signals and a fog light was installed with a switch in one of my rear back up lights. Therefore, my symptoms may have something to do with the wiring when it comes to my lights, but I could not say for sure.

Overall---

I hope this post will help anyone having similar issues that I had with my G35. Thanks again to tjrob2000 for reaching out to me for an update.

 

Be careful with ILSCO DE-OX or any other type of coating compound. These are intended to be applied AFTER the connections are joined together and tightened. ILSCO DE-OX forms a seal around the connection and works well to prevent oxidation of the connection. Coating items, then assembling them may lead to insufficient amperage transfer of the connection.

 

ILSCO DE-OX is designed to be used ON the mating surface.