Alternator, Battery,or Ground

[jim@detroit]

Ok, I have a 2002 Explorer, 4.0 XLT, 140k miles, I put a rebuilt alternator from Advance Auto in June of this year after the original one died while on the road. This caused the truck to use the battery as the electical source which then caused the battery to loose its charge. The new alternator was switch out and all ran fine untill about 6 weeks ago. The battery is a Die Hard about 3 years old.

Now the problem: The head lights the tail lights, dash, dome light dim and once I turn the car on in the morning. It looks more like they pulsate.
I put a volt meter on the battery this morning and it read 12.4 volts before I statred the truck. The Alternator read 13.9 to 14 volts once I started the truck and stayed there.

Well, one other bit of information; If the truck is off and I turn the head lights on
they do not pulsate,dim, flicker they stay lit.

I just put new motocraft plugs and new autolite wires along with cleaning the idle control two days ago and its still doing it.
Help in Detroit!!!!

 

[matt0248]

Use you volt meter and check for AC voltage. It shouldbe under a few hundred milivolts AC. if there is too much ac voltage the alternator couldhave a bad diode.

 

[Squirrelmaster]

It is not unheard of to have a bad alternator right out of the box, so the voltage regulator could be an issue as matt0248 said. The other thing to check is the battery itself, as an alternator dying can often be a death knell for a battery, especially if it is a few years old.

Tom

 

[jim@detroit]

Why would my lights only pulsate while the engine is running and is this a clue to a bad altenator. What would cause the battery to act this way.

 

[matt0248]

Why would my lights only pulsate while the engine is running and is this a clue to a bad altenator. What would cause the battery to act this way.

Your alternator when spinning (engine running) produces an AC (alternating Current) voltage. This AC voltage is rectified by the diode bridge making it essentially DC voltage. If there is too much AC "leakage" the lights will get brighter and dimmer as the AC voltage rises and falls. That is why the problem goes away when the car is turned off. No more alternator spinning and no more AC voltage.

 

[Ronin8002]

Bad voltage regulator on the alt maybe?

 

[Allmost 50]

I know I'm drawing at straws here. The last time I saw lights pulsate on a vehicle it was caused from a shorted hot wire on the downstream side of a circuit breaker (not fuse) that fed another item. This was on a Fire pumper.
Do your light pulsate randomly or something like 1 second dim and 3-4 seconds bright.

 

[jim@detroit]

The light flicker and its quite noticible, along with the tail lights , the dome light and dash lights
I think Im just going to have to take the altenator off and have advance check it out.

 

[1Aauto]

The light flicker and its quite noticible, along with the tail lights , the dome light and dash lights
I think Im just going to have to take the altenator off and have advance check it out.

Jim, if you really get stuck on this one we sell new alternators,for a pretty good price. I don't have one on the site for your application,but if your in a bind let me know and I'll see if I can get one for you.

There's no core charge on ours either.Those rebuilts are hit or miss.

Tony