Before you scream alternator......This one is 10 monthes old and I've had it checked 4 times at different places with everyone saying it's working perfectly.

What happens is this: Most times (not ALL times) when Im driving my truck at night the all of my lights get dim/bright sporadically---even at WOT. My truck never acts like its going to die or anything, the lights just flicker.

I have a 2 gauge ground cable going from my battery to the intake manifold and this has worked perfectly for the last 3yrs. I tried cleaning the contacts points of the cable and even reconnected the factory ground to my ground. <img src="/forums/images/graemlins/angry.gif" alt="" />

Anybody want to take a shot at this one?

Later this week when I get a chance I'm going to add several more grounds around the engine bay (like those aftermarket grounding kits) and see if it was just interference or something <img src="/forums/images/graemlins/confused.gif" alt="" />

Check the headlight switch and its wiring, I think the headlight switch is a grounding type, with the switch grounding out relay circuits to make the lights work. I only have the '92 to '95 Factory manuals, so I can't be sure about your '97. I can check how the earlier models were wired up for this if you want. Also, when the problem is happening, you might want to pull over and check the available voltage to the headlight with a voltmeter to see if it's close to what you read when touching the battery posts while the Monty is running. Should be close to altn output voltage.

Yeah if you don't mind finding out where the switch is I'd really appreciate it!

One question. Does the frequency of the flicker vary with engine speed, or is it constant? Does it still happen when you are sitting still with engine running. Does it happen with engine stopped?

I don't think a failing diode in the alt. will always show on an alt. test until it goes all the way, except as a slightly reduced output, which is hard to test for on an auto parts store tester with a dummy operator.

Well I just turned on the truck and revved the gas and it made the lights flicker quickly but when I let it go back to idle and revved again---it didn't affect the flickering at all. When the truck is just idling it still flickers.

it doesn't seem to do it when I turn the key to turn on the dash lights but leave the engine off.

So you are saying it does not change in flicker rate with the change in engine speed, and doesn't flicker when the engine is off. I think that rules out the alternator since I'm pretty sure it's output varies in frequency with engine speed. That leads me to think that it's somehow related to the presence or absence of basic engine vibration - engine running = constant flicker, and enigne off = no.

The main things I'd check first are the headlight switch in the cab - wiggle it, tap it, look at it close and see if it jiggles slightly with the engine running, say 2800rpms or so, all while watching the lights for any flicker that you can correlate to your switch twiching. Try all the tests but the run-jiggle test with the engine no running to make a single flicker easier to see. Then I'd find and try the same stuff on the headlight relay in it's socket. My 89 is tucked up in the front of the DS fenderwell in the engine compartment. Don't know where yours is, but bet it's close to there. Look for a relay panel with markings. I think mines about 1"w x 2"l x 1.25"h plus lectron prongs.

If your headlights go off when you turn the ign switch away from "run", try jiggling the key and tweaking the lock/switch assy slightly in an alternating key rotation movement around the run position.

The FSM has wiring diagrams, component location drawings, and test routines, and unless you get lucky with the above, is the best bet for a quick correct fix.

The ground idea may not be off base. I'd check the common ground lug nearest the column as a first guess, and the FSM with show you for sure where it is. FSM has common ground point location drawings and diagrams, too. Look for a single bolt or nut on a stud (probably a 10mm) with more than one black wire of medium gauge with ring lugs grounded there.

Oh, yeah, and after FIRST disconnecting the battery, tighten the 10mm nut holding the fat wire to the back of the alternator. This nut is connected to full battery amperage with a fat wire and only maybe a fusible link of 100amps or so 12v+ straight to the battery, and failing to disconnect same will teach you impromptu welding with a wrench and/or a fried fusible. Why do they call them fusible links and fuses when they burn in two? You don't fuse "them" (there's only one in the circuit), you destroy it's built in amperage rated fusion - you unfuse it. But if you called them unfusible links, people wouldn't buy them 'cause they'd figure they didn't work....

If you need a good general reference on light bulbs post on this board, click here.

I had exactly the same problems in my 88 and it turned out to be the light switch, $145 new at the stealer, and problem solved <img src="/forums/images/graemlins/kewl.gif" alt="" />

Well I played with the light switch and it didn't do anything.

I haven't had a chance to mess with anything else and to tell you the truth, if it ends up being a $150 switch then I'm just going to deal with it for now <img src="/forums/images/graemlins/frown.gif" alt="" />

Sorry for the delay, I was VERY sick last week and forgot that you posted a request for more info. OK, after checking the ETM, seems like all '92-'95 Montero's here in the US use a grounding point at the backside of the battery area, on the inner side of the l/f fender for grounding the headlight switch. And yes, it's a ground switch, so that header junction which is the ground point next to the battery probably has multiple black wires going to it. Remove your battery if you can't get good access to it, but it's there that the headlight circuit ends.
Mitsu calls it Ground Point #3 in the ETM
For the rest of the circuit, it runs like this on the power side for your headlights[maybe for your '97]
Power out of fusible link at battery, goes to headlight relay, which is located in the relay box next to the battery . Grounding for the relay is fed directly to the headlight switch, and once the power out from the relay passes through your headlight bulbs, it ends up at the headlight switch, waiting to be connected to ground via the switch to that ground point on the inner side of the L/F fender.
Hope this helps you out.

2000 montero limited, non-sport. when highrevving engine, lights flicker. what gives?