dim headlights get brighter as rpms raise

kilog55 · Post by **kilog55** » Wed Mar 12, 2008 8:39 am

what would cause this bad voltage regulator? or is it the Alt. kind of annoying waiting to get pulled over for something as stupid as this. all the lights do it even the dash lights

kaptnkaos · Post by **kaptnkaos** » Wed Mar 12, 2008 10:59 am

Sounds like the alternator to me kilog55...

You could try the old remove the battery cable trick.
If it keeps runnin' after you remove the cable then it isn't the alternator...

KaptnKA

S

Thunderfoot · Post by **Thunderfoot** » Wed Mar 12, 2008 11:34 am

That is usually a sine of the Voltage Regulator not working correctly.

kilog55 · Post by **kilog55** » Wed Mar 12, 2008 4:39 pm

ahh geez now im confused

ill try option number one first

kaptnkaos · Post by **kaptnkaos** » Wed Mar 12, 2008 5:10 pm

Hey kilog55

Let us know what it ends up bein'...
When it comes to electrical stuff, I trust Mr Thunderfoot 100%...
I had always been told that when the lights dim off like that when rpms are down that it was the alternator.
I've not had to deal with that problem before so I'm not not 100% sure...
I know that if the engine dies when you pull off the battery cable then it's the alternator...

KaptnKA

S

basketcase0302 · Post by **basketcase0302** » Wed Mar 12, 2008 5:27 pm

kilog,

I would say the voltage regulator too.

Do you have a voltage meter to put on it?

Should be no less than 11.5 @ idle and around 12.5 above idle.

Jeff

kilog55 · Post by **kilog55** » Wed Mar 12, 2008 5:52 pm

no i dont, and i should have one as all i own are old trucks

l1k2gadd · Post by **l1k2gadd** » Sat Mar 15, 2008 8:18 pm

The headlights dimming as the RPMs of an engine dropping and then getting brighter as the RPMs increase IS usually a sign that the voltage regulator is not functioning correctly. What is happening is the headlights are feeding directly off of the alternator. As you drive if you watch your light they will get so-o-o bright as you run down the road because the current to them isn't being regulated and being kept constant.

My daughter's 1966 Mustang was doing this. The instrument lamp in the car were getting so bright, as the headlights were, as I was running down the road. When I came to a stop sign or a red traffic light the headlights would drop to an off-white color and the instrument lights would be so dim it was hard to see the instrument panel. I put a voltage regulator in the car (it had the original 1966 voltage regulator on it) and that fixed it.

Chaseman · Post by **Chaseman** » Thu Aug 14, 2008 3:01 pm

I had the exact thing in my 1966 mustang happen , I mean the exact thing.
Althrough it was kinda cool cause at night when the car was idleing with the running lights they looked alive , they had a beat to them.

Wes · Post by **Wes** » Fri Aug 15, 2008 3:47 am

Belt might be slipping make sure it tight and not glazed.
Alternators do not charge well at low rpm, have any pulleys been changed ? Also check for good clean connections at alt, reg, batt, and solenoid.

ToughOldFord · Post by **ToughOldFord** » Fri Aug 15, 2008 5:42 pm

I always thought that was a symptom of a bad diode in the alternator.

Never found out for sure though, had the problem many a time, always ignored it. As long as the battery stayed charged that's all I cared about.

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