Alternator question

[AMC]

Hello all!
Have a 2000 xlt 4x4 88,000 miles. Noticed that when I turn on my headlights the dash and temp/compass displays go dim. By what I've read it sounds like an alternator. It looks to be original (motorcraft). I replaced the battery about 4000 miles ago with a motorcraft. How do I diagnose this problem? And where exactly are the voltage checks to be made, at the battery or at the alternator?

Thanks!

Tony

 

[pbnj22]

voltage checks should be at both... car off and at battery.. should read 12.6 or so... car on ad idling and at battery should be 14.7 or so... higher than 12.6 though since that is what a battery sits at and you want to charge it you need to be ABOVE 12.6.. then you can carefully check alt while running.. be careful of fan and belts etc. but this reading should be same as battery when running.. if it is higher at alt than at battery then you have wiring issues from alt to battery... check those things and post results

 

[pbnj22]

on a second thought.. maybe this is normal? in any car if you turn your headlights on your car would assume its night time and dim your gauges so you dont get blinded by bright lights during night? if that makes sense..

 

[koda2000]

most auto parts stores will test your charging system for free. you don't mention having a BATT light on, so it could be the alternator has lost a diode and isn't charging 100%.

 

[Maniak]

on a second thought.. maybe this is normal? in any car if you turn your headlights on your car would assume its night time and dim your gauges so you dont get blinded by bright lights during night? if that makes sense..

Yup, this is normal behavior on most "newer" vehicle.. Normally they do this to the Radio, clock and any other extra things that lit up to see. They need to be really bright during the day.. and if you have your lights on they don't need to be as bright..

This can get somewhat anoying though.. our '06 mustang has this and we run with the fog lights on all the time. We use them as DRL and as soon as we turn them some of the things get dim and hard to see in the daylight.

~Mark

 

[AMC]

Thanks for the replies. I tested the voltage at the battery with the engine running and found it at 14.6 vdc. Lights on it dropped to 14.2 vdc or something like that. I think you folks nailed it by saying that it is a normal function. First off, none of the other interior lights go dim and my gauge remains steady while I switch lights off and on. I think what caused me to notice this just now is that I'm in upstate NY for a few months and it seems to rain here every day. The law here is that when your wipers are on so must be your lights. Not so in California (which I'll be happy to get back to). Thanks again for the info.

TC

 

[koda2000]

Thanks for the replies. I tested the voltage at the battery with the engine running and found it at 14.6 vdc. Lights on it dropped to 14.2 vdc or something like that. I think you folks nailed it by saying that it is a normal function. First off, none of the other interior lights go dim and my gauge remains steady while I switch lights off and on. I think what caused me to notice this just now is that I'm in upstate NY for a few months and it seems to rain here every day. The law here is that when your wipers are on so must be your lights. Not so in California (which I'll be happy to get back to). Thanks again for the info.

TC

sounds normal to me.

 

[SoNic67]

The law here is that when your wipers are on so must be your lights. Not so in California (which I'll be happy to get back to).

That's common sense. Most eastern states have that rule.
I hate when I drive on rain, limited visibility, and I suddenly arrive behind some idiot driving slow, with lights off, on left lane...
Maybe is better for you to go back in Kalifornia, if that's too hard.

 

[pbnj22]

That's common sense. Most eastern states have that rule.
I hate when I drive on rain, limited visibility, and I suddenly arrive behind some idiot driving slow, with lights off, on left lane...
Maybe is better for you to go back in Kalifornia, if that's too hard.

Agreed I live on the edge of Lake Superior and the fog gets ridiculous and people leave lights off... Pisses me off.. Turn them on or don't drive!

 

[my98nnj]

Make sure the dimmer is turned up. Sometime a wipe of the dash moves the dial slightly.

 

[AMC]

Maybe is better for you to go back in Kalifornia, if that's too hard.[/QUOTE]

Again, thanks for the replies. And yes, it is better for me to go back to the Golden State although it is quite beautiful here.

TC