Charging Light comes on at Idle

[Joey4420]

So it has been a long road.  Engine rebuild, multiple turbo rebuilds and I will get my car back next week if all goes well.  Now I have been told I have a charging light that comes on after idle for a minute or so.  Alternator was bench tested and test good.  Battery has been fully charged.  Car runs and drives wonderfully, but light comes on.  I opted to fix the light myself as I am pretty sure I can figure it out, but thought I would ask in case someone has ideas before I grab the book and multimeter and start digging.

 

Does anyone have thoughts on why it would show a charging light on idle when the alternator has been tested good and is basically brand new less than 2500 miles on it.  (rebuilt original)

[CarBuff]

Hey Joey,

Testing alternators is often performed at higher RPMs. (as in, a load test)

 

So, they could be saying it it working....but in the idle condition it's NOT. Something else might be amiss.

 

So,

30 minutes ago, Joey4420 said:

thought I would ask in case someone has ideas before I grab the book and multimeter and start digging.

GRAB THE MULTIMETER. Report the battery voltage readings at rest; at idle; at 2000 RPM; and 2000 RPM with the lights and interior fan on HI. (Loaded)

 

+++++++++

 

My anecdotal experience:

 

Our '88 suddenly showed a low/wavering voltage while driving. (Older Esprits have a voltmeter, are you jealous?) I brought the car to an auto electric shop, and they said "the charging system is fine, the alternator is providing 70 amps"😮

 

Our Esprit has a 90 amp alternator!!!!!! 😬 The issue turned out simply to be a loose alternator belt. (Anybody noticed that modern belts don't squeal when loose? )

 

So, if your multimeter doesn't show 14.5VDC over 2000 RPM, first look at the belt's adjustment. THEN see if the alternator is putting out at idle. Original 4 cyl Valeo alternators don't...

 

Do you have the Caddy Catera alternator fitted?

[Joey4420]

@CarBuff I will check, but the dealership said it showed charging good at idle and at RPM, I will verify.  The belts are all new an better be tight after the fun of the rebuild and turbo issues.  I am hoping to pick the car up soon and I will update as soon as I get it in my garage.  

[andyblackman777]

Mine was doing that and it was ok at first showed good charge etc but  then eventually started to misfire. changed alternator all fixed.

failing that could be a bad earth somewhere??

[Joey4420]

@andyblackman777 Hoping for a bad earth at the dash.  

[Thartje]

2 hours ago, Joey4420 said:

@andyblackman777 Hoping for a bad earth at the dash.  

Pretty unlikely unless someone has been in there messing with the wiring. Alternators wear out, or wiring that is exposed to the elements would be the next thought.

[lotuslover1]

i have the same issue,i replaced the alternator a few years back with the lighter/smaller version.At idle im getting 13.7 volts,battery replaced 2 months ago with brand new bigger unit.

[CarBuff]

Awaiting Joey's multimeter test. 🤨

 

EDIT: Make sure you tell us voltage AFTER 2 minutes (since that is what the dealer said).

Edited January 27 by CarBuff

[lotuslover1]

i will check after 2min,not sure how belt can be loose since the tensioner acts on its own

[Escape]

Your right, belt slippage is very rare with the later multi rib belts, but was a common problem on the older V-belts.

[Joey4420]

I think I may have found the issue.  I will double check when I get back from a work trip.  The positive battery terminal although tight can become loose if twisted.  Well some bad roads and a stop found be with zero power to even run the radio.  Pushed to the side of the road to find if I turned the terminal even 1/4 turn it became very tight.  So I got home and added a battery post shim.  Hoping this is the fix, simple and easy.

[jannickz]

Check the battery cables for corrosion, tightness, and damage. Loose or corroded connections can cause voltage drops and trigger the light.