electrical grimlins/pulsating lights

[flathead6]

My 92 has been experiencing power surges. The lights, exterior and interior, pulsate. This is not related to the heater grid since it happens constantly and even in 90 degree plus temps. I have added ground straps from the engine to frame & body but with no success. The volt guage varies from 11 to 12. 5. I have been getting an engine fault code of 12-46-55 occassionally and more consistantly lately. The manual says that's high voltage at the battery. My question is: is this the alternator or something else? NAPA wants $125 for a rebuild. What can I do to narrow down my problem? Any ideas out there? Thanks guys.

Keenan

 

[1stgen4evr]

grimlins

They are tricky little boogers and you may have to isolate some of the circuits to know for sure. Disconnect the trigger voltage on the heaters and see what that does. Your computer (Does the 92 have a computer?) might be telling them to come on regardless of the ambient temp due to a faulty sensor. Then disconnect the alternator and see what that does. If the alternator is putting out sufficient voltage, you can disconnect the ground at the battery and the truck will continue to run. If the alternator is dead, the truck will quit. One thing for sure, the voltage is low at the numbers you mention.



You may not have a good ground at the small wire comming off the battery to the core support. That will have intermitent influence on a lot of the electrical.



James

 

[Paychk]

The fault code 46 equals high charging voltage, 12 is battery recently disconnected, 55 is end of codes.

I would check the grounds near the battery, there are 3 wires that should be attached to the radiator support. They should be clean, bright & tight; the factory just screwed them down and didn't remove the paint. So pull them and sand off the paint, clean the terminals and re-attach.

Next I would pull the alternator and take into any parts house and have it tested, there may be an internal fault.

 

[ARhine]

I have had the lights pulsate on my GM rigs when diodes were going bad in the alternator. Nice thing about the GM stuff is the alternators are like $40 rebuilt.

 

[paccool]

The 92 has a PCM (power control module) and the voltage regulation for the alternator is done there. Is there any problems with the AC or cruise not working? These usually quit when the PCM is going south along with the voltage regulator.



How old is the battery and have you had any problems with it holding a charge?

 

[flathead6]

The "12" fault code threw me off because the battery hasn't been disconnected for a long time (years?). The "46" seemed logical since its an electrical problem but I've never seen the volt guage dance or spike and I've been watching it alot lately!

I'll revisit the ground straps issue and double check to make sure all connections are clean.

Hadn't thought about the heaters cycling due to bad sensor. I can't remember how the lights behaved last winter when the grids ran. I know I don't hear the "click".

After that I guess I'll take the alternator in to be checked, need to swap out the belt anyway. Whats the little black box connected to it where the wires come in? A noise suppressor? NAPA said the regulator wasn't in the alternator but in the computer, does that sound right? The NAPA guys here are usually pretty good but its hard to know everything.

Thanks guys.

 

[flathead6]

Missed your post paccool when I replied a second ago.

The cruise works fine, I never use the AC but I'll check.

The battery was on the truck when I got it a couple years ago and has been doing fine, I'll check the age. The problem came with the truck but seems to be getting worse or at least more annoying, the fault codes were just occasional at first but I am getting them fairly regular now. I at first assumed it was just low idle speed since it goes away with revs but I installed a tach and idle is correct. If you stand outside and look at the lights it looks like you are flashing them hi & lo. The problem is more noticble in the cab since I added aftermarket guages which show the light pulses but the problem was there before that.

Is the regulator part of the PCM or just down there with it? PCM, I assume, are not cheap?

KB

 

[Paychk]

Alternator is regulated by the PCM, some have changed it over to the old style Dodge Voltage regulator. Do a search and you'll find the instructions for it.

One other possibility is the wire that feeds back to the battery, it has two heavy quick disconnects, the one near the battery can get severely corroded, the other is near the bank of relays on the inner fender, try pulling them apart and soak in baking soda water if you find corrosion, dry & coat with dielectric compound.

 

[paccool]

Seeing your description of the lights looking like they are going from high beam to low when the voltage fluctuates, I think James may be on to something about the grid heaters working when they should not be. If the thermoswitch in the air intake is shorted they could do that.

 

[flathead6]

I'll check my battery connections and see about disconnecting the heater grids. The battery didn't have a date so I'm not sure of the age. The pulsating is rapid, like two cycles per second. Reminds me of a disco- I hated that back then too.

KB

 

[RonA]

My truck has been doing this for about 6 months. Lights pulse about 2 times per second. I changed the alternator and have changed the voltage regulator a couple of times. (yes, my truck has one). Am starting to check grounds and connections. If I figure mine out I'll let you know. But no luck so far. My computer does not know the motor is running, and if you unplug the regulator the pulsing stops.

 

[flathead6]

Well I guess there can be comfort in numbers huh? How did you disconnect the regulator? Do you get any fault codes?

KB

 

[backroad]

Hey, even my F350 Ford has the flickering light syndrome... ..... Of course almost every thing under the hod is '93 Dodge/Cummins... ... And the alternator is triggered by an early voltage regulator and there are NO grid heaters in the wiring at all just yet.

 

[flathead6]

Looks like paychk may have exercised the gremlins. This morning I pulled the positive connections as suggested and cleaned and greased. One was kind of corroded. So far so good. No more pulsations and no fault codes yet. Time will tell. I'll check the lights after dark to be sure. I was hung up on the grounding and charging system and it seems to be as simple as a hot wire with poor connection. Thats why the forum works, thanks guys. RonA- check those pos wires!

KB

 

[Paychk]

I hope that was the trick, plz keep us all posted!

 

[flathead6]

Yep, several days and NO more pulsations. Whew, what an easy fix. Thanks again guys.

KB

 

[Greenleaf]

My 90 exhibits the same problem. The volt meter dances. I cleaned all the grounds and no luck there. The DVOM will read a steady 14. 4 volts when I'm testing but the interior lamps and the head lamps are flashing to the beat of the volt gauge.



I'll try cleaning some more connections as well.



GL

 

[WGREEN67]

greenleaf, i had the same problem with my 91. 5, it has the regulator on the firewall. i first replaced the regulator (because it was cheep and easy) it seemed to "fix" the pulsing, after about 2000 miles the pulsing started again than it would just stop charging. bought another regulator and cleaned all the grounding wires in engine area, no change. i have the ND (denso) type alternator, i found a new brush kit for these online @ fostertrucks.com under the dodge parts area. installed new brushes and charging has been ok for 200+ miles..... hope this helps, BILL