Instrument cluster dimming at idle

[Gsmblue]

Last night I drove Elyza (F350) for the first time.

The HiPO bright white LEDs are fantastic, I had to dim the instrument lights.  When I got home and the engine dropped to idle the lights dimmed to almost not visible then as I revved the engine they came back.

I am assuming the alternator may be on the way out, but  am also away it could the voltage regulator or the regulator on the back of the instrument cluster.

Basically I am looking for advice on the appropriate trouble shooting to work this out, all advice is welcome!

[kramttocs]

Was it only the instrument lights? Could you repeat the test with the headlights and courtesy lights on?

[Gary Lewis]

If you had the A/C and lights on it is probably just because the alternator can't keep up.  You are still running the original 1G, right?

[Gsmblue]

I did not notice the headlights dim, but this is something I will check.
The AC was on, i did not turn it off and see if that changed anything.
It is a 1G alternator

So far 2 fingers pointing at the alternator. I will get the DMM out see what the voltage is at idle..

[Gary Lewis]

The 1G can’t keep up with headlights and A/C when idling.

[Gsmblue]

Thanks Gary.

I never noticed in the other trucks before, last night was the first time.

Sounds like I need to do 3x 3G conversions, but which one first???

[FuzzFace2]

Gsmblue wrote

Thanks Gary.

I never noticed in the other trucks before, last night was the first time.

Sounds like I need to do 3x 3G conversions, but which one first???

The only time this might be an issue is if you are sitting at an idle for a L O N G T I M E with everything running.
I ask how often will this happen?
It sounds like this is the first time since you had the truck and if me would not worry.
Dave ----

[Gsmblue]

This is true. I did have the stereo cranked up too.

I may only have noticed as I have the LED dash lights in now and they went from bright to almost off.

[rcarlisle]

How do you identify what alternator you have?   Mine loks new - may have already been replaced by the PO.  I notice the signals seem slower when the AC is on.  Don't notice any dimming of anything though.  And have been running the AC a LOT lately.  I have this pic.  Does that tell anyone anything?

[Gary Lewis]

An '81 should have a 1G, which has an external fan and external regulator, which is the box on the fender by the starter relay.

The 2G, aka Firestarter, came out in '86 and has an external fan but internal regulator - no box on the fender.  The main problem with them is that the output connectors can develop a bad connection and start heating, which makes the connection worse, which causes more heating, which...

The 3G came out in the 90's and has both an internal regulator and internal fans.  It was a serious redesign and puts out more current at idle than either the 1G or 2G do at full tilt.

[rcarlisle]

Ok, looks like 1g in mine.   Do I test the voltage in standard method - across the battery terminals with everything running?  

[Gary Lewis]

Yes, that's a good way to test.  The 1G is adequate for a truck with standard options, inc A/C.  But if you have the A/C and headlights on and the engine idling the alternator can't provide enough current to power them so the battery will make up the difference.  That's fine unless you do extensive idling or add other power-hungry devices like a large stereo amp or electric cooling fans.

[rcarlisle]

I'm old enough to remember when ALL vehicles did these gyrations of lights dimming, slow signals, etc, depending on engine speed.   At least the truck has a big enough battery to not panic when you listen to the radio with the truck off.   Back in the day we did that a lot - wash the car with stereo blasting with windows up.  My new car gets in a panic if I try to listen to radio with car off - gives me constant WARNING messages.  

Usually when the sun goes down, it starts getting cool enough for windows down.  My preferred way of travel.