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yudamann · 02-15-2009, 06:43 PM

We have a 2005 Allegro Bus 38 ft. on a Freightliner chassis. The driver's instrument panel consists of 2 ea. 4 in. dia. main gages and 4 ea. smaller gages all with backlighting that appears to be center mounted bulbs behind the gage face. The backlighting intensity is controlled by a rotating wheel on the headlight control subpanel. The intensity of the instrument lights is very weak, even with the wheel adjusted to full brightness. At dusk, it is almost impossible to read the gages. Could this be due to burned out back lighting bulbs? Is there a fix for this problem, perhaps an after market lighting system? Any help with this problem would be appreciated.

Joe-K · 02-16-2009, 04:12 AM

On our Allegro Bus (Spartan chassis) the dash illumination is controlled by a rocker button dimmer switch. It seems to have about 9 or 10 steps from full bright to dim.

When we first go the rig, I noticed that the dash illumination was dim, so I measured the voltage coming out of the dimmer module. What I was seeing is that the dimmer module was not outputing the full voltage when set to the maximum brightness setting. In reality, it seemed to only vary the output voltage on the lowest settings. Tiffin sent me a replacement module under warranty which solved the problem after replacing it.

I'd suggest on your rig, to remove the instrumentation panel from the dash and look carefully behind it at the bulb wiring. You should be able to see the bulb wiring and hopefully measure the voltage across the bulbs. If you see over 12 volts, then the dimmer is working, but if the voltage is low, then I'd suspect the dimmer is faulty.

While the instrument panel is removed, you'll also have the ability to see if any of the bulbs are burned out or dislodged from the panel.

yudamann · 02-16-2009, 05:31 AM

Thanks Joe-K. I will give your advice a try and hopefully find the problem.
Did your replacement switch improve the lighting significantly?

Joe-K · 02-16-2009, 06:34 AM

Changing the dimmer solved my issue, but it was obvious that I had a bad dimmer since I was only getting voltage out of it on the lowest settings. As I turned it brighter, the lamps actually went out.

Your's may be a different issue so it's best to measure the voltage at the lamps.