Update on flickering dashpanel illumination problem = Resolved

I have had the problem that my dashpanel illumination lighting erratically and randomly flickers on and off and usually stays off most of the time.
Before I start the engine, when I turn on the parking or full headlight system using the switch on the stalk, the dashpanel illumination comes on strongly and does not flicker or go out.
But with the engine running, the dash lighting comes on and goes off with seemingly no rhyme or reason. (I have the Daytime Running Lights (DRL) system with this 2005 Sprinter 3500 built out as a Winnebago View RV).
I posted this problem on the forum a few years ago and had suggestions that: 1 the DRL fuses (under the drivers seat) can affect the dash illumination; 2 the dash illumination going out can be an indicator that the side marker or rear license plate lights are not working; and 3 that cleaning the wiring connections on the back of the dashpanel may help solve the problem.
Last evening, I spent a few hours trying to track down the source of the problem.
The exterior side and plate lights all work fine when the dashlights are out, so that does not seem to be the problem.
The last thing I want to do is pull apart the dashpanel to clean wiring connections, so I concentrated my attention on the fuse box below the drivers seat. Interestingly, I now found a pattern to the dash lights going on and off.... when weight goes onto and off of the driver's seat, this seemed to relate to the lights going on and off.
I check all the fuses related to the DRL system (#2, 8 13 & 14) and the dash illumination (#3) and all are tightly fitting, have continuity and have 12volts on each side of them when in place, so the fuses are good.
Sitting in the driver's seat, once the dash lights went out, I found I could turn the lights back on by reaching down and lifting up slightly on the fuse block under the side of the seat, when I released the upward pressure on the fuse block, the lights went off again.
FINALLY, I figured I had found the source cause of the problem.... BUT;
I next loosened (and subsequently re tightened) the two torex screws that hold the fuse block in place, and the dash lights went off and stayed off, nothing I touch, move or wiggle in the wires and fuses under the seat brings the dash lights back on.
So now I am stumped again as to what is causing the erratic dash lighting. The lights are now off and will not come back on when the engine is running (with the engine off, turning on the headlights on the stalk switch still does turn on the dash lighting!)
Is there a ground wire connection (that may be loose) at the drivers seat fuse block that would affect only the dash illumination? (When I pulled out fuse #3 (dash illumination) the dash lights go off and I get a warning beep, and as I do not get the warning beep when I have this light off problem, I do not think this fuse or connections to it are the cause of the problem).
How do the dash light systems work that the dash lights come on using the lighting switch on the stalk with the engine off, but this switch will not bring on the dash lights with the engine running?
Any help or suggestions about how the dash lighting system works, and in particular how the circuit is connected with the engine on and with it off, would be appreciated.
I guess my next step will be to remove the drivers seat to see what I can find in the wiring and fuse blocks in the seat pedestal.
Terry,
2005 Sprinter 3500 base to a 2006 View

Re: Update on flickering dashpanel illumination problem

Should i assume you have the 2006 (close enough) service manual (which locates splices and ground points in sect 8w-91)
If not, it's here: http://diysprinter.co.uk/reference/2006-VA-SM.pdf

The DRL system is mostly covered in the "Front Lighting" section (8w-50)
The instrument lights are powered via splice S316 feeding the "lamp driver" input on page 8w-40-7
..and S316 is powered on page 8w-11-25 <<-- i'd start here

Vic has been finding that some connections (and wires) are missing in the Lighting areas of the circuit diagrams (just to add to the fun).

good luck hunting...
--dick

--dick

Re: Update on flickering dashpanel illumination problem

Dick, thanks for your reply and the link to the sprinter manual. No, I did not have the manual, so your link to the manual is most helpful.
In studying the wiring diagrams, I find that there are 3 DRL relays (left side, right side and one for DRL lamps) and the circuitry thru these relays is what powers the left headlight assembly, which is what feeds back power to the dash light driver. These relays are located under the drivers seat and as weight in the seat seems to affect the dash lights, I will check these relays tomorrow.
I would suspect a loose power or ground connection at the dash light driver connections, but as these are located behind the instrument cluster, I do not see why moving the under seat fuse block would affect the dash lights!
Will let you know what I find, hopefully it will be a resolution to the problem and not more questions!
Terry

Re: Update on flickering dashpanel illumination problem

I finally solved the flickering dash light problem.
I pulled off the driver's seat to access the relay block, started pulling relays to identify which ones controlled the Daytime Running Lights and the dash light driver power. Turns out at least 6 different relays would seem to be powering the DRL circuits. After lifting out the fuse block and the bracket holding the relays, I found one wire with a clip end on it had come loose out of one of the relay bases.... plugged this wire clip firmly back into the relay base and Voila the dash illumination lighting is working again.
When I had isolated the flickering to happen when weight was on the driver's seat, I figured there had to be some loose wire connection somewhere in the seat pedestal. It was not obvious from the wiring diagrams what might be feeding power to only to the dash lights, I guess I could not decipher how the DRL circuits work to see that one wire being off a relay would knock out just the dash lighting.
On to my next Sprinter issue!