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Dash gages going crazy (long post)

Yahoo Message Number: 68387
Today I had a strange problem. I installed two 12V plugs one form the Chassis battery distribution box and one from the Domestic batteries, for that one I picked up a DC source at the door switch panel. After installation everything seemed normal. Started the coach voltage came up to about 14v on both Chassis and Domestic batteries. I was reading with my plug in voltmeters and checking with my Fluke and they all agreed. I decided to check the exterior lights. Fog and side lights OK. Turned on the headlights and all the engine instruments drove full scale and the Tach went to zero. All the exterior light were on and bright. The volt meters I had plugged in showed no change. Put my fluke on the dash volt gage and it showed a -6.6 V, turned off the headlight switch and everything went back to normal. I traced the power wire from the distribution box and the voltage was correct. I pulled the fuses on the two 12v plugs I installed to see if that had any impact, none. I found another strange thing when adjusting the rheostat for the dash light dimmer I found that when set to minimum all gages appeared normal, but when I went to max brightness the gages went full scale. Now the turn signals and the exhaust brake make the instrument fluctuate wildly. I have run out of ideas.

Jack Allure 40 1997 30076 Cummins 325

Re: Dash gages going crazy (long post)

Reply #1 –
Yahoo Message Number: 68389
When you hit this kind of erratic behavior, look for what they all have in common. The ground. Start looking at ground wires in the dash area for starters.

Leonard Kerns

97 Magna 5418

Re: Dash gages going crazy (long post)

Reply #2 –
Yahoo Message Number: 68424
Ken here, I agree start from the Ground from the source the fuse box negitive and check all ground's and Negative looke for burned or LOOSE CONNECTIONS!. Working on old Cat DC Gauge panels most of the time was the problem, I would start with a test light and go through the above hoops Turn on and off lights and DC Loads and see what happens. My old Allure has had no problems so far as you have. Please keep us posted! Ken in Yuma 99 Allure 30356.

Re: Dash gages going crazy (long post)

Reply #3 –
Yahoo Message Number: 68473
This is a follow up on the gage problem on my coach. I was unable to find a bad ground in the harnesses. I found the ground feed wire to the dash lights and gages and routed a separate ground wire to my ground post and the problem was solved.
I want to thank Leonard and Ken for getting me on the right track looking at the ground system.

Jack Allure 40 30076

Re: Dash gages going crazy (long post)

Reply #4 –
Yahoo Message Number: 68474
Glad you found it Jack. Over the years have spent way to many hours trouble shooting things that just did not make sense until I finally started to think of ground first. Pour ground causes some of the most weird things to happen. Good call on running a new ground wire. Could be a break inside a wire. Have seen that more then once.

Leonard

97 Magna 5418
 

Re: Dash gages going crazy (long post)

Reply #5 –
Yahoo Message Number: 68522
Ken here, Thanks for sharing, I all my years the biggie was as I taught fellow tech's look for green stuff on the Battery terminals and start from there. I need the Brain streached now and then. Great Group and enjoy reading and sharing life's exp. We always may not be right but I lost many a service call to the islands off Miami helping end users on the phone and for free! Thanks for sharing. Ken 99 Allure 30356