[khgeisler]

OK, I have an issue with the back lighting for all my gauges.  Currently, none of them light up.  I see they are all daisy chained together and are controlled by a dimmer and turn on with the headlights.  I also have 4 or 5 dash post lights that work perfectly and the dimmer works perfectly.

I pulled one of the lights out and powered it up and it lit up, so the bulb and socket was good.  But when reinstalled it does not work.  However, when I adjust the dimmer from low to high (or high to low), the voltage for the batteries drop from 12v to 8 or 9v's.  Seems to me something is shorting to ground.  What do you all think?  Have the dimmers been issues in these rigs?  I could switch the dimmers and try that, just the dash panels looks delicate.

Does anybody have a source for the dimmers?
Does anybody have a source for the sockets and bulbs for the back lighting.  I tried to remove the bulb to get some and broke the bulb, so I am not sure if they are removable from the socket?

[HoosierDaddy]

I would be checking for ground on the light circuit. Where did you measure the voltage drop?

[khgeisler]

I would be checking for ground on the light circuit. Where did you measure the voltage drop?

The voltage drop was the volt meter gage for the chassis batteries.  It's kinda freaking me out.

[Richard]

So…………keep in mind that the analog VDO gauges work off ground. Before totally freaking, I would put a voltmeter on the chassis batteries and recreate the scenario that caused the dip on the gauge.

Your problem with all the lights not working and the wonky gauge could be as simple as a ground circuit.

Newell daisy chained the grounds for the instruments. Bad practice in hindsight. When the ground deteriorates so does the accuracy of the gauge. It is the primary reason that most run VMSPC or some other instrumentation software that takes its signal from the DDEC engine computer.

[khgeisler]

So…………keep in mind that the analog VDO gauges work off ground. Before totally freaking, I would put a voltmeter on the chassis batteries and recreate the scenario that caused the dip on the gauge.

Your problem with all the lights not working and the wonky gauge could be as simple as a ground circuit.

Newell daisy chained the grounds for the instruments. Bad practice in hindsight. When the ground deteriorates so does the accuracy of the gauge. It is the primary reason that most run VMSPC or some other instrumentation software that takes its signal from the DDEC engine computer.

Richard, I used my 12v test light ground lead to add a ground to the backlight circuit.  At first nothing changed, I removed the test light ground and what do you know, everything was working, even the dimmer.  I do have VMSPS, but I am OCD about things working like they should as a double check.  I will keep looking for the gremlin.  What a wiring nightmare, with ne access.