47heaven Posted November 13, 2009 Report Posted November 13, 2009 Last week, I had installed a new battery and alternator, and since then I have noticed that at night time, while the car is idling, the lights are at a certain brightness, but when I rev up the engine they get brighter and then dime back down after I let off the gas. I thought this wasn't supposed to happen with a 12v system, especially with a new battery and alternator. Any ideas of what's causing that? Quote
Plymouthy Adams Posted November 13, 2009 Report Posted November 13, 2009 not enough current being output by the alternator...happens with any voltage systems whent he regualtor does not meet the demand of the system..check your connections real good especially the ground on the alternator itself...there is usually a post on the alternator for a dedicated wire..suggest trying that. Else you will need to test the alternator with a shunt...if you take this to a auto house for testing, remember not to let them test for more than 60% of the alternator rating...them folks sell a whole lot o alternators after they finish their test... Quote
Don Coatney Posted November 13, 2009 Report Posted November 13, 2009 What is your amp gauge readings through the dim/bright cycles? I recall when idiot lights were first used on cars to replace the amp gauge. These were 12 volt cars with alternators. The way I could tell if the charging system was working was to observe the interior lights at night with the engine at idle and the head lights on. Then race the engine and watch the lights get brighter. I dont think you have anything wrong. Quote
greg g Posted November 13, 2009 Report Posted November 13, 2009 Check your ground connections also. While not a sensitive as with 6V, dim lights with 12V can still be attributed to iffy grounds. Also you might want to add a ground strap between the body and frame or engine. What type of alt are you running? The single wire style needs a fairly high rpm to put out siginificant current. So your idle speed may not meet that threshold with higher loads. Is your alt wire through the amp gauge or to directly to the battery? Quote
Norm's Coupe Posted November 13, 2009 Report Posted November 13, 2009 You might want to check your fan belt too. If you don't have it tight enough the belt slips a little and the alternator can't supply the right amount of current to the car. I would check that before checking the electrical hookups. Quote
Young Ed Posted November 13, 2009 Report Posted November 13, 2009 Greg you gave me an idea for my daily driver. Its getting rusty now and I wonder if I've lost a good ground for my headlights. They were really dim and I polished the lenses which got them better but I still think they aren't as bright as they should be. Quote
Plymouthy Adams Posted November 13, 2009 Report Posted November 13, 2009 my left one went way dim this morning as I rolled to the stop on Alt 247 intersection...time for a new bulb Quote
greg g Posted November 13, 2009 Report Posted November 13, 2009 (edited) Ed, by all means check your grounds but ask also how old are the bulbs. They will degrade over time as the tugstun deposits itself on inside of the bulb.. The deal with halogen is that is that it is supposed to slow that process but it doesn't eliminate it. My wife's car is a 2000, and I just polished the lenses and changed both bulbs (original to the car) as one blew out. Quite a noticable difference. Edited November 13, 2009 by greg g Quote
Young Ed Posted November 13, 2009 Report Posted November 13, 2009 I can't recall the last time one of them blew out. But Im sure neither have been replaced since they blew out the last time. I know I have a ground at the cowl but any ideas where else to look? The front fenders are becoming nonexistent so if the ground is supposed to travel through them that could be an issue! Quote
greg g Posted November 13, 2009 Report Posted November 13, 2009 the head lamps usually take the shortest path possible for the ground wire. So lengthening the wire to a good clean ground couldn't hurt. Quote
B-Watson Posted November 14, 2009 Report Posted November 14, 2009 Whether single wire or double, makes no difference. The alternator should be putting out a charge even at idle. If you are sitting there with your high beams on, heater fan going full bore along with your rear window defroster, you might get a slight discharge, but not a dimming as you describe. What is the amp rating for your alternator? Years ago I had a 1974 Plymouth Sebring, 318, and the bearings went on the alt. Had it replaced with a rebuild. That night the lights on the car were dimming at idle which it never did before. Turned out the rebuilt unit was a 30 amp - the unit it replaced was a 40 amp. Put a 40 amp alternator in and no more problems. The regulator is the same for both a 30 and a 40 amp alternator, by the way. Bill Vancouver, BC Quote
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