Fading lights

[Jim Miller]

When I start my 70 CDV (with door open) I noticed the interior lights brighten and diminish. As can be typical they can brighten when increasing engine speed, but it can also brighten and diminish regardless and can dim in spite of increased engine speed. I'm thinking perhaps voltage regulator (it's the original). But before I do anything I've found it wise to post and gather input.
Thanks

[bcroe]

It could be weak wiring, see if the voltage is
steady at the battery.  No, look for an alternator
problem.  Failing diodes can do that, not hard
to find an open diode with a meter after it is
apart.  good luck, Bruce Roe

[Jim Miller]

Will do - thanks

[Jim Miller]

Before starting, the battery was 12.5 volts. Didn't change much at idle. When revved, it momentarily raised to 15 but dropped off to 12.5. Then I did try a new voltage regulator which seemed to correct the waivering the interior lights, but no voltage increase with rev and the GEN light stayed on. Bench test next.

[bcroe]

Not an expert at external regulators, but you
do get regulation with revs.  I think it is
the alternator, diodes. 

Ought to be a test for that, I can see the
waveform with missing peak on a scope, probably
would sound different?  Put a cap in series
with a speaker?  Bruce Roe

[Jim Miller]

Update on my suspected issue. Had alternator rebuilt. Replaced battery. Tried new AC Delco USA made regulator and got worse results that before. Here is where I am at with original regulator - At idle I read 13.30 volts at the alternator and battery but I get waivering courtesy lights. Turn on headlights with high beam and I get readings in the low 12's and continued waivering lights - GEN light does not come on. If I rev the engine I can get readings of 13.40 - sometimes the lights brighten and sometimes not but continued waivering. Could this be a possible issue someplace in the lighting wiring or light switch?

Any suggestions on where to check further appreciated - auto electric is not my strong suit and frustrating.


PS - When I tried the new regulator (tried 2) at idle I got a reading at the battery and alternator around 12.5, idle with lights on 12, and revved with lights on 11.9.

[dn010]

Try cleaning up your grounds/ground wiring.

[dplotkin]

Jim:
If you've got the original mechanical regulator there you are almost certain to need a new one and I'd suspect before your 10DN Delcotron. But there is an easy test that will prove one or the other of the regulator or alternator as the culprit to wit:

Pull two pin harness connector from the back of the Delcotron. Place DVM across battery. Run engine at high idle while using a jumper wire to jump between the Delcotron F terminal and the output stud. This takes the regulator out of the equation and drives the Delcotron to full output. You might see as much as 17 volts and if so you know your Delcotron is on the job. After you have a reading remove the jumper. Get a new regulator.

Dan

[bcroe]

If the above test clears the regulator, I would
still suspect a bad diode in the alternator.  It
is not difficult to take it apart and check the
diodes.  good luck, Bruce Roe

[V63]

If memory serves a bad diode cause an electrical draw when the vehicle is keyed off?
Parasitic draw

[dplotkin]

If memory serves a bad diode cause an electrical draw when the vehicle is keyed off?
Parasitic draw

This is true. A bad diode will cause reduced DC output, a run down battery and can cause the GEN lamp to glow dimly.
HOWEVER, diodes are far less likely to fail over a mechanical regulator which is guaranteed to fail at some point as will an incandescent lamp. He should swap his regulator and re-run the full field test. I doubt its a diode.

Dan

[Jim Miller]

Yes - I tried a new AC Delco made in USA regulator with poor results. So the alternator professionally rebuilt, new battery, new regulator, checked fuses. Next week going to start looking again at grounds.

[V63]

Slipping drive belt?

[Jim Miller]

Slipping drive belt?

Its snug with about 1/2 inch deflection

[wheikkila]

Your new regulator needs to be adjusted. When I have a generator or alternator rebuilt with an external regulator. I always take the regulator in at the same time. They almost always have to adjust the regulator.
      Thanks Wayne

[bcroe]

All alternator diode failures I have seen were
open circuit, easy to measure.  This will not
cause a slow drain, but it will cripple the
output of the alternator.  I have also seen it
somewhat light the GEN light because when the
open phase comes around, internal alt voltage
that was supposed to charge the battery will
instead rise up until the next phase comes
around.  Easy to see the irregular waveform
on a scope. 

Maybe I never saw a shorted diode, because that
would cause a fault current that soon blows it
open?  Bruce Roe

[TJ Hopland]

Is the regulator for sure getting a good ground?  They usually ground through the body to the body which is possibly a long ways from the alternator.  Maybe just for testing add grounds between the alternator and regulator and body.   

[Chopper1942]

I believe TJ has the right idea.  The issue is either high resistance grounds or high resistance in the battery sense wire for the regulator.  Remove all the ground cables from the body, frame, and engine and polish their contact point.  Put star washers between the cable and body, frame, etc.

To diag the system you need a DMM and a jumper wire.

I don't have a wiring diagram, but if I remember correctly the regulator may have 4 wires to it.  Red/orange B+, white is generator output sense, brown B+ with KOEO, and the blue field wire, which turns on the generator (alternator is Chrysler nomenclature GM was a Delcotron). KOEO there should be B+ at the RD/ORG and BRN wires.  If not, RD/ORG may have a fuse or fusible link blown and if no B+ at BRN wire check charging light. It should be on. If not, bulb is burned out or open in light circuit from ign switch to regulator.  With the engine running, back probe the RD/ORG wire and there should be >13.0V at the red/org wire if it is charging.

If not charging and you have B+ at the RD/ORG wire connect a DMM to the generator output terminal (RD/ORG) and battery neg cable. Now, install a jumper between the RD/ORG wire and the BLU wire at the regulator. KOER. This should drive the generator to full output.  If it now charges and the charge light is out, you either have a bad regulator or regulator ground.  Do not leave the jumper in place very long. It can drive the voltage very high and cause damage.

Some applications had a dedicated ground wire from the generator and the voltage regulator so both are on the same ground plain.  If yours does not, I would install one.

Hope this helps with your diag and just throw parts and money at it.

[Cadillac Jack 82]

Grounds, wiring, bad regulator, Alt going bad.  All of these will cause that.

[Cadillac Jack 82]

Also grease on contacts for the body strap contacts will cause this.