Why do my interior lights pulse like a disco ball gone bad?

[nwoods]

When the engine is idling, my interior lamps all pulse and glow rhythmically. All the lights pulse at the same frequency. When the engine is off, no problems, nice and steady.

What exactly is causing this (besides the engine, duh!)?
Is something wearing out? Will I need to be replacing something soon?

 

[jeep-N-montero]

Alternator maybe? Cleaned your battery contacts lately?

 

[dixie1865]

Alternator maybe? Cleaned your battery contacts lately?

Alternator would be my guess. When you are at idle it's producing fewer amps. When you rev the engine alt output increases. When the engine is off you are getting a nice steady draw from the battery.
I had the same experience with a truck (years ago) and it was the alternator.
If you are able, I would pull it and take it to a local parts store and have it checked before you fork out the money for a new one (in case it's something else).

 

[jlocster]

I agree with jeep, probably a bad alternator but clean your battery terminals first.

 

[jeep-N-montero]

If it is the alternator then have it rebuilt for higher output, because this will give you an excuse to buy a winch.

 

[nwoods]

Hmm. I replaced the battery and alternator less than 12 months ago.

 

[bikerjosh]

I subscribe to the idea that given the season your Montero has become possessed by the ghost of some studio54 fatality who is reliving the glory days. :wings: or the alternator.

 

[nwoods]

I subscribe to the idea that given the season your Montero has become possessed by the ghost of some studio54 fatality who is reliving the glory days

Looking at pictures on Google, I can certainly hope that's the case!

 

[nwoods]

AutoZone

 

[mires]

Have you used a multimeter to test the alternator? If you put it on the battery terminals when then engine is running, you should see between 13.8-14.2 volts or real close. If you see it dipping when the disco starts, I would say it is your alternator as well. I'm not sure what kind you put on it, but I have discovered over the years that an alternator is one of those parts you really need to get at the dealer. Don't waste your time with the parts store, rebuilts or high output units. 9 times out of 10, you will regret it.

 

[off-roader]

One alternative to a dealer alternator ($$$$$) or aftermarket rebuild/new alternator is to find a local rebuilder. Most not only have to stand behind their work but also a long warranty isn't goo enough... Otherwise their reputation and business will suffer.

theres one both myself and Grasscat use here in San Jose. I'm sure you can't find a decent rebuilder near you as well.

 

[nwoods]

Love the Disco GIF Mr. Mires, thank you.

So I don't know if these readings are good or not, but with a multimeter on the the battery, I get a solid steady 12.75V with the engine off. With the engine on, it's stays in the 14V range, but does fluctuate between 14.2 and 14.8. The refresh rate on my meter doesn't seem to correspond to the frequency of the pulsing engine, so it's hard to measure the timing of the fluctuations. However, I did note that the fluctuations where only at low idle. if I apply a few RPM's to the engine (such as high idle, or slightly above, around 1200 RPM), it smoothed out to about 14.5v, and the dome lights stayed steady. It's only at low idle that I am getting the disco fever effect.

 

[plh]

Didn't read back in the whole thread, but did you check integrity and tightness / clean the battery ground cable connection to the frame and engine?

 

[jlocster]

Nathan, your voltage seems to be in spec, but what you are not considering is amperage. It's possible for an alternator to put out the proper voltage, but the amperage output could be faulty (too low in your case). Given your dimming lights I'm guessing this is the condition...the alternator is not outputting enough amperage at idle to power your headlights/gauges etc. You won't know for sure until you measure output, but you'll need a special tool for that...a clamp on ammeter is easiest.

Since you also mentioned you bought the rebuilt alternator at Autozone, I wouldn't be surprised if you got a bad one. At least they have a lifetime warranty. Just be wary if you take it back. Make sure they do a load test (amperage) and not just a voltage test...be prepared for them to only test voltage and claim the old one is still good.

Like plh and the others have said, check the easy stuff first: battery cables/connections, ground straps, terminals, etc.

 

[nwoods]

Hmmmm.. sounds like I'm going to have to yank this thing out either way. Thanks guys, I really appreciate the help. The thimble I keep all my mechanical knowledge in is slowly filling up