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Gauges change with headlights


slaterson1
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Kind of a strange issue, when I turn the headlights on some of the dash gauges move. For example, the fuel gauge goes from 3/4 down to almost 1/2 when I pull the headlight switch, some but not all other gauges do the same, drop down to a lower reading. Any ideas where I can start when diagnosing this?

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We see the same thing, 2000 Diplomat. I've just relied on the ScanGauge D output for accurate readings. I noticed recently, however, that the analog tachometer bounces a bit, so have been meaning to look closely at the wiring. I'm sure it doesn't help that one of our cats climbed up under there on a recent trip. But the shift in the gauges has been there for the 18 months we've owned the coach.

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The wiring harness has multiple grounds crimped to a single wire of the same gauge scattered all over the coach. Many are buried in the harness and nearly impossible to find. When I replaced my gauges I ran individual ground wires to a grounded terminal strip located in the front bay. I also grounded every thing else in  the general  vicinity in a similar manner.

 Then with a label printer I labeled each conductor with its terminal number and name which includes both source and load.  This is the method which is used in industrial  systems which require a higher level of reliability and ease of troubleshooting. 

When you label a fused conductor it should include the location,  fuse number and load description in the same manner. 

The most fun was with a pair of wire cutters dumping the Monaco crap in the garbage can.

 

Edited by Gary Cole
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Consensus seems to be grounds, which I will check, clean and tighten as many as I can find. In the meantime, my BlueFire digital dash is accurate so this is all probably an annoyance rather than a serious issue. 

11 hours ago, DrDon4u said:

Clean your GROUNDS!!!!

 

WHY ARE WE YELLING? LOL

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The way I troubleshoot is I make a long lead (50-ft) and attach one end to the chassis battery negative terminal. The other end to my voltmeter.  Then I use the other lead from the voltmeter to test for voltage on ground terminals.  They should vs 0.0 Volts, or very close to that.  Do this with the headlights on.  A quick confirmation can be done by checking the closest ground for the headlights.  You will likely see 0.5 or more Volts.  Working your way back, you should find a place in the grounding where that voltage drops.  That is your problem area. 

  - Rick N

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I pulled my dash apart yesterday in search of an issue of the speedometer glitching out when the lights are on. Also fuel gauge drops when lights on.  I found every connection loose on the back of the gauges, almost like they were finger tightened when assembled.  The worst was the ground connection to the speedometer which was just barely engaged with the nut backed all the way off.  Seems to have addressed the issue.

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