M20S Replacing Rheostat Box with Dimmers - Wiring Question

[Darrolio]

Hello Mooney Masters - 

Daylight savings is upon us, and it is time to repair my panel and glareshield lights as they have not worked for some time, limiting me to daylight flying. I read other posts on this site regarding replacing the rheostat box, and many recommended the MaxDim switch (instructions at this page). Savvy also recommended this switch, as it is FAA STC Approved / PMA'd. I received the two switches, and the instructions say to "Determine the Positive supply, Dimmer circuit, and chassis ground wiring."

With the attached schematic, it seems...

Positive:
LP06E20 - panel lights positive supply
LP02E20 - glareshield lights positive supply

Ground:
LP11D20 - though it looks like I will have to split it into two wires, one for each dimmer

The Dimmer Circuit is throwing me for a loop, making me think this is above my head. 
For the panel lights, I assume:
LP73A20 - GPS Ann
LP12C20/LP14D20/LP03C20 bundle (compass, map, panel)

For the glareshield, I'll crimp:
LP07E20

But what is the LP19C20 bundle of wires that includes Panel Lights (Signal Out), Glareshield (Signal Out), and Lights (Common)?

Also, bonus points for someone who can point me to the right inline fuse box that the kit recommends, but does not include. 

Hoping someone has accomplished this and can provide some guidance.  I can crimp wires and test current, but I'm no electrician. 

Thank you and happy night flying!

Darryl

Edited November 11, 2023 by Darrolio

[Darrolio]

Deb pointed out that I should try looking at the Dimmer Box schema, which I have attached here. Thanks Deb!

I honed in on the Light Control Box b/c the wire labels are a perfect match for that schematic. 

Behind the panel, the wires going to the Dimmer Box are as follows: 

LP06E20
LP11D20
LP73A20
LP02E20
LP03C20
1-3 Cluster of: 
LP12C20
LP14D20
LP07E20
3-1 Cluster LP19C20 of: 
Grn
Wht
Blu-Wht

These labels all appear on the Light Control Box schematic, but only a couple appear on the Dimmer Box schematic.  Odd. 

Googling how to read schematics...  

Edited November 11, 2023 by Darrolio

[RoundTwo]

On my J, there are two fuses on the bottom of the dimmer box. Most likely you don’t have a wiring problem, but a problem with, or within, your dimmer.

As a side note, Daylight Saving Time (DST) ended last Sunday, so in actuality, Standard Time is upon us.  I’m also very envious that you have such a clearly legible wiring diagram.

[Darrolio]

Thanks RoundTwo - I opened up the dimmer box but no such luck - no fuses in or on our box... or in-line on the wires.

I'm also normally a stickler about savings and standard time, but translated the lack of light lately into "savings." 

[Richie the C]

On my J, there are two fuses under the dimmer. They are incredibly expensive, if I am shopping for the correct fuse, at $479 for ten. Ours blew the fuse when it was replaced, so no dash lights. Anyone else had a problem with these fuses?

Thanks

N9930S

[RoundTwo]

6 hours ago, Darrolio said:

Thanks RoundTwo - I opened up the dimmer box but no such luck - no fuses in or on our box... or in-line on the wires.

I'm also normally a stickler about savings and standard time, but translated the lack of light lately into "savings." 

Check pin 9 for ground and pins 7 and 2 for voltage from circuit breakers. That will tell you which direction you need to go next.

[PT20J]

2 hours ago, Richie the C said:

On my J, there are two fuses under the dimmer. They are incredibly expensive, if I am shopping for the correct fuse, at $479 for ten. Ours blew the fuse when it was replaced, so no dash lights. Anyone else had a problem with these fuses?

Thanks

N9930S

Can you install standard standard AGC type fuse holders somewhere around the dimmer controls and wire in place of the expensive fuses?

[Darrolio]

3 hours ago, RoundTwo said:

Check pin 9 for ground and pins 7 and 2 for voltage from circuit breakers. That will tell you which direction you need to go next.

Ok I’m at the plane now. I checked these - they are both getting ~24 volts.  

I have also mapped out all the pins and wires… it actually seems miswired according to the schematic. I will draw a little diagram and post tonight.  

[Darrolio]

The plot thickens...

First, when I said the lights haven't "worked for some time," I meant that they have not worked for as long as I've had the plane (~1 year). My father, who I got the plane from, swears they worked, but can't remember for sure. He says it checked out each time during annuals... but Glareshield was noted INOP on my annual. 

Both Panel and Glareshield wires have 24V power - I checked today per RoundTwo's suggestion. 

However, I found that the switches were cross-wired (you will see this in my pin diagram here in orange highlight, when compared to the Light Control Box schema): 

• The Panel switch has the panel power, but wired to Glareshield out
• The Glareshield switch has glareshield power, but wired to Panel out

So - the behavior seems to be: no light on either glareshield or panel, but the map light under the yoke stays on all the time no matter what. 

What I plan to try next: 

• Cut wires LP07E20 and LP03C20 and cross+crimp, then try the old control box.  
• If that doesn't work, connect LP07E20 (circuit), LP02E20 (positive), and Green / White-Blue / LP11D20 (ground) to the new dimmer and see if that makes the Glareshield work. 
  • If so, connect up the other dimmer. I'm not quite sure what to do with the GPS Annunciator wire, as it is going through some fancy box on the circuit board, but will try to wire with the circuit.  
• If that doesn't work... time to fly it to my mechanic (during the day). 

Finally, I do not plan to install the inline fuse, as the kit recommends, since I have breakers. 

Sound like I'm on the right track? 

Thank you for all your help so far!  

Edited November 12, 2023 by Darrolio

[Aerodon]

Darryl

Did you buy 2 MaxDim, or a combined unit?  I went with the combined unit, so I can delete the incoming wire and associated circuit breaker to 'create' more panel space. 

I'm using one output for 'glareshield' and the other for compass, panel post lights and avionics (minimal).

But no harm in installing 2 MaxDims and then keeping the same 'split' that Mooney used.

You are correct, the Mooney drawing is hard to read.  It looks like the glareshield and panel lights are grounded back to the unit via the shield?  Look further down the Mooney drawing to see what they did?  There is probably a quick connect near the glareshield?

I don't understand the 'ground to decease panelights' is there a bright/dim switch somewhere?

 

Aerodon

 

 

 

 

 

 

 

 

[Darrolio]

I purchased the 2 MaxDims. 

I went last night and experimented with switching the orange highlighted wires to match the schematic, with the original dimmer box. This put the glareshield, compass, and map light on one switch, so it must be miswired on the other end too. These lights were also not dimming... just coming on at a low light.  I decided to cut the wires at that point and hook up the MaxDims. 

Once all hooked up: 

• The glareshield lights work beautifully now.  Full range up to pretty bright. 
• The compass and map light work great - full range.  However, the instrument panel lights still are dark. 

I tested the power coming out of the dimmer for the panel lights, and get ~24VDC. So the issue was a combo of the dimmer box and something further down the line for the panel lights. 

Now I'm not sure where to look next in regards to the instrument panel lights... 

[Pinecone]

On 11/11/2023 at 10:04 AM, Darrolio said:

I'm also normally a stickler about savings and standard time, but translated the lack of light lately into "savings." 

If you are a stickler, it is Daylight Saving Time, not "savings." 

 

[JimK]

My glare shield and instrument lights didn’t work on my Ovation 3 when I bought it.  I took the dimmer box apart and found two things wrong.  1. Someone had installed one of the large voltage regulator transistors backwards which caused the pins to short out against the clearance holes in the heatsink.  2. When it was powered up the shorted pins caused the transistor and a resistor to burn up.  I replaced the those components and the lights work fine now.  I had to order more components than I needed so I have some if anyone else finds that their box has the same problem.