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Headlights / Cabin Lights dim with electrical load

My Belov’ed 96 Nissan Sentra has me scratching my head. Most noticeable at night, when headlights are on, I notice when a load is applied, (power windows used, fans turned on, brake-lights / turn signals switched on) all the headlights and cabin lights dim for a fraction of a second and return to normal brightness.



I’ve read all the suggestions on lots of forums;

New battery (6 month old Optima Red-Top) Checked voltage on battery. Reads between 13.5 and 14v.

Checked battery terminals. All clean and bright and tight

Brand new alternator (maybe 2 months)



My next thought is, replacing the battery cables. Worth a shot?



Every piece of advice i get is “check the ground”. I am really hoping that that doesn’t mean checking EVERY ground in EVERY circuit?

Have you checked the other end of the battery cables, the one away from the battery’s terminals? If the ground connection has high resistance it’ll “drop” voltage.

It sounds normal to me. When light bulbs or motors are starting up they draw a lot of current.

Why would you want to spend any time/money on such a condition?

Wasn’t that way when I bought the car. The condition also has degraded over the last few months.

Because the car is bought and paid for, and I would like to correct the problem before it becomes worse.

I’m with you CavemanDave - most people pay no attention & ignore things. Check & clean up all the wires - focus on battery cables and charging system wires and those grounds. And just have the charging system/battery load tested. The easiest way is with equipment that luckily large auto parts stores will use on your car for free.

Is it really getting worse? Like, very noticeably worse?

What are the devices that you’re turning on that are causing the dim? Thoughts off the top of my head:

-Heater blower is going out and drawing more current than usual.
-Radiator fan is getting a little older and drawing more current than it used to.
-Fuel pump is getting old and drawing more current than it used to.
-Car is not idling as high as it used to and not spinning the alternator as fast as it needs to in order to maintain output.
-Corrosion or contamination inside the shielding of the battery cables
-Corrosion or contamination at the alternator connections
-Any combination of those things

I know you don’t want to hear it, but honestly, unless it’s getting seriously bad, I think that’s acceptable.

Now, is the time to do some voltage drop tests. If you want to be sure that an electrical connection is good (has no electrical resistance–ohms) you perform a voltage drop test on it. A voltage drop test is just placing a volt meter probe on each side of the connection of a wire having voltage and noting any voltage indication. If there is a voltage indication, that is your voltage drop caused by resistance (ohms). You CAN’T see if a connection is electrically sound. That’s why you have to actually measure it.

Have the battery load tested. Even a new battery can have problems. Is the reason you have a new battery because the old battery was doing the exact same thing?

It’s been getting worse since it started about 6 months ago.

Lights dim when you use anything that would draw current. Power door locks, power windows, brake lights, turn signals, sun-roof, blowers, the list goes on.
Car is idling right at 850rpm right where the FSM indicates. I confirmed this on the last emissions test.

I’ll go with the third to last point. Hence the reason I want to replace the battery cables. Alternator’s brand new, so there shouldn’t be any problem with it’s connectors.

Considering the age of the car, yes it probably would be acceptable, but I don’t want to overlook something small that could turn into a much bigger problem later on.

I replaced the battery because around October it was becoming harder and harder for the starter (the starter was replaced early last summer) to crank the engine over. I decided to change the battery before it stranded me.

That’s my plan for this weekend. Also probably have it load-tested when I head over to the autoparts store.

The primary ground you want to check first is the chassis ground. It is typically the smaller black wire coming from the battery minus terminal going to the vehicle body.

Thanks for answering my confused bit about WHAT GROUND TO CHECK.

Only problem with your answer, is there’s only ONE negative lead on my battery. I’m going to check it anyway.

While your checking things check the alternator belt tension.

Yeah, that’s why I said typically. Follow that wire, it may attach to the engine block first and then branch over to the car body. Some go into a power distribution box and then branch off to various places. There’s no standard and it seems each mnfr is different. The chassis ground is common to the systems you described and is often bolted to the fender. It’s there that corrosion often occurs and develops a high resistance connection.

Look for a ground wire between the engine and the firewall or fender.