Instrumentation Grounding

Topic: Instrumentation Grounding (Read 949 times) previous topic - next topic

Instrumentation Grounding

January 04, 2020, 12:53:02 am

The dash instrumentation acts erratically if I turn on the lights or run the fan or use the turn signals. I figured it was an issue with the grounding so I did a little digging. I found the ground strap, in the dash, that all of the electronics terminate too was corroded in half and not providing a useful ground. I wasn't able to determine exactly where the other end of that strap terminates but I did find a very similar looking strap in an electric panel in the compartment next to the fresh water tanks.

The cable tray that runs the length of the coach is so packed with hoses and cables that it is very difficult to trace down anything from one end to the other and most of the identification tags are all worn out or missing. If I could verify that the strap in the panel is the same as the one from the dash I was going to try to use a fiberglass wire fish rod to run a new ground strap. If I am unable to trace down the other end of the ground strap I was going to try grounding the dash half to the chassis similar to an automobile to see if that made any difference.

Does anyone know if the dash ground strap is the same one that I found in that electrical panel?

Can the 12V electrical components be grounded to the chassis similar to an automobiles without any negative side effects or will it not make any difference?

I know that the grounding strap comes in contact with the chassis in multiple places on its journey but I wanted to ask about grounding directly before proceeding.

Thanks in advance
Tyler

Re: Instrumentation Grounding

Reply #1 – January 04, 2020, 08:48:29 am

Quote from: The Soft Boulders – January 04, 2020, 12:53:02 am

Does anyone know if the dash ground strap is the same one that I found in that electrical panel?

I don't know for sure, but I seriously doubt that the woven ground strap in the dash is one end of a very long strap that runs all the way back to the DC electrical panel in your center storage bay. It is more likely that the dash ground strap is bolted to the nearest main chassis frame component. Same with the strap you found in the electrical panel.

In my experience, DC grounding in any vehicle always goes to the nearest part of the metal frame. The frame is usually grounded at one or more points to the engine block. The engine block is grounded to the battery NEG post. The complete electrical circuit for any device on the vehicle must always originate at the battery POS post and terminate at the battery NEG post. The ground path normally runs through the frame.

There is not a lot of metal "frame" in the nose of the GV. The ground strap in your instrument panel probably drops down under the floor and is bolted to the chassis there. You can do the same thing with a new grounding strap or cable. Just make sure the connection to the frame is on clean bare shiny metal, and it should work fine.

NOTE: All the above is my opinion based on personal experience only. I AM NOT a certified electrician, but I do strive to act like one.

Re: Instrumentation Grounding

Reply #2 – January 04, 2020, 09:58:17 am

Assuming ground from frame to battery is good, you can ground to any clean metal on the coach for those low amperage loads.

Re: Instrumentation Grounding

Reply #3 – January 04, 2020, 10:20:24 am

Quote

Does anyone know if the dash ground strap is the same one that I found in that electrical panel?

On my 97 the braided ground wire runs from that connection point mid coach directly to the instrument panel ground location.
jor

Re: Instrumentation Grounding

Reply #4 – January 04, 2020, 10:25:52 am

Quote from: Chuck & Jeannie – January 04, 2020, 08:48:29 am

I don't know for sure, but I seriously doubt that the woven ground strap in the dash is one end of a very long strap that runs all the way back to the DC electrical panel in your center storage bay. It is more likely that the dash ground strap is bolted to the nearest main chassis frame component. Same with the strap you found in the electrical panel.

In my experience, DC grounding in any vehicle always goes to the nearest part of the metal frame.

That's what I figured as well and why I was so surprised to find that long ground strap. I will get back under there and do some more research. That strap starts from the ground block and the disappears into the dash somewhere. That long strap start from underneath very near where the one disappears but they might actually not be the same. I was doing a bit of assuming that they were one in the same but can't actually verify. It's all fiberglass under there so I dont know where it would go if they're not.

Re: Instrumentation Grounding

Reply #5 – January 04, 2020, 10:42:59 am

Short, fat "grounds" (actually the connection to the reference/return current path) are generally the best way to go.

Current flows in a loop, and needs to get back to its source to complete the circuit. It WILL take the path of least impedence. If your "ground" connection to the return current path is a long, effectively thin connection, that will most likely be higher impedence than other options for the current to get back to its source.

The rogue current flowing in unexpected paths back to its source can play all kinds of tricks.

"Ground" is a misnomer that drives EMI engineers nuts. "Ground" is a place where potatoes and carrots grow

Re: Instrumentation Grounding

Reply #6 – January 04, 2020, 10:47:15 am

Quote from: jor – January 04, 2020, 10:20:24 am

On my 97 the braided ground wire runs from that connection point mid coach directly to the instrument panel ground location.
jor

Thanks jor, i feel a little more confident now. I will probably try grounding both the end from the dash and the end from the panel to the chassis to help complete the circuit more efficiently.

Re: Instrumentation Grounding

Reply #7 – January 04, 2020, 10:53:05 am

Quote from: Michelle – January 04, 2020, 10:42:59 am

"Ground" is a misnomer that drives EMI engineers nuts. "Ground" is a place where potatoes and carrots grow

I'm a simpleton so please excuse my use of incorrect terminology. Hahaha

Re: Instrumentation Grounding

Reply #8 – January 04, 2020, 11:02:12 am

Quote from: Michelle – January 04, 2020, 10:42:59 am

Short, fat "grounds" (actually the connection to the reference/return current path) are generally the best way to go.

"Ground" is a misnomer that drives EMI engineers nuts. "Ground" is a place where potatoes and carrots grow

So what do the EMI engineering gurus call it?

"Connection To The Reference/Return Current Path" is a kinda big mouth-full for casual conversation.

Perhaps it is shortened to a acronym? CTTRRCP would be much easier to say!

Re: Instrumentation Grounding

Reply #9 – January 04, 2020, 11:35:10 am

Quote from: Chuck & Jeannie – January 04, 2020, 11:02:12 am

So what do the EMI engineering gurus call it?

"Connection To The Reference/Return Current Path" is a kinda big mouth-full for casual conversation.

I would like to know also.

I don't mind sounding like a big dummy but I've learned that using the correct terminology can be very beneficial when asking for assistance. Not only for finding the solution, but people of knowledge are often more apt to offer assistance when they feel they're dealing with someone who is at least somewhat competent.

Re: Instrumentation Grounding

Reply #10 – January 04, 2020, 02:40:06 pm

Quote from: Chuck & Jeannie – January 04, 2020, 11:02:12 am

So what do the EMI engineering gurus call it?

I was poking fun, since I used to be one of the them

It was drilled into my head to never simply call it "ground" lest that imply a giant "voltage sinkhole" where all the current flows into but never out of and where it's always 0 volts. We always prefaced it with a descriptor (although one of my senior colleagues always used "reference" rather than "ground". Chassis ground (for the metal enclosure of the computer), card ground (for the PCB reference "0" voltage and which was rarely a quiet, steady voltage), safety ground (the green wire that goes to the lug on the plug).

Some fun reading from that colleague Planet Analog - The Ground Myth -

Re: Instrumentation Grounding

Reply #11 – January 04, 2020, 03:04:43 pm

Sorry - that article was way over my (potato) head.

I actually always preferred the British term for (electrical) "ground".

My DW owned a 1970 MGB for several decades. There was a decal in the engine compartment that read "This Vehicle is Wired Negative Earth".

To a classic science fiction aficionado (me), that statement seemed to suggest that the car came from a alternate universe where everything was the exact opposite of our "Positive Earth". Of course, I was drinking a LOT of Boone's Farm Strawberry Hill in those days...

It was somewhat of a letdown to find it only meant that her car (unlike earlier MG models) had a negative (chassis) ground electrical system.

Re: Instrumentation Grounding

Reply #12 – January 04, 2020, 05:50:35 pm

Somewhere along the line Foretravel seems to have changed from the "earth" side of the circuits being local frame grounded to running a separate green "earth" wire to every circuit.

80's coaches were grounded(earthed) to the local metal frame component. After time and use if you turned on or off a local circuit switch some or all adjoining circuits would flicker.

Our 97 has no flicker. But the push on connectors in the dash were loose. Pull. Crimp tighter. Reinstall. Fixed intermittent gauge readings.

Re: Instrumentation Grounding

Reply #13 – January 04, 2020, 08:20:44 pm

I still use the term "earth" even after 53years in Canada
JohnH.

Re: Instrumentation Grounding

Reply #14 – January 04, 2020, 10:52:43 pm

Quote

don't know for sure, but I seriously doubt that the woven ground strap in the dash is one end of a very long strap that runs all the way back to the DC electrical panel in your center storage bay.

Seeing is believing. When I get a new coach I always locate as many ground points as I can and clean them up. I traced that braided wire from that mid coach DC panel to the dash.
jor

Re: Instrumentation Grounding

Reply #15 – January 05, 2020, 12:12:39 am

You may make a solid connection under the dash and drop a big wire to the frame and ground near the headlights. Should be a ground screw up there.

Re: Instrumentation Grounding

Reply #16 – January 05, 2020, 09:01:27 am

Quote from: jor – January 04, 2020, 10:52:43 pm

Seeing is believing. When I get a new coach I always locate as many ground points as I can and clean them up. I traced that braided wire from that mid coach DC panel to the dash.
jor

jor,

I don't doubt what you found on your coach, and I did say "I don't know for sure...". It just seemed more logical (and efficient) to me that both of those straps would attach to the nearest frame member. But when did the "Foretravel Way" ever have anything to do with LOGIC?

Re: Instrumentation Grounding

Reply #17 – January 09, 2020, 12:11:39 am

I was able to get the braided ground strap pulled through to the panel and removed. The part of the strap that had been protected from the elements was in pretty good shape and had a nice 3/8 terminal where it connected to the panel so I ended up using part of it up front in conjunction with the other section. I was unable to get the dash section pulled through but luckily there was enough of it in decent shape to attach to the frame. I fastened the dash end to the frame with two 1/4-20 bolts by tapping the frame.

I removed all of the accessory grounds and added the second piece of braided strap to the top side of the bolts and then fastened the other end to the frame with a 3/8-16 bolt. I sanded everything that had corrosion/oxidation on it and applied liberal amounts or di-electric grease to each contact point.

The braided ground strap was roughly 35' in length and was labeled on both ends with matching numbers, confirming it was the same strap.

So far all the gauges are acting fine without any fluctuation when running of the accessories. Even running everything at the same time didn't cause any anomalies.

Re: Instrumentation Grounding

Reply #18 – January 09, 2020, 02:46:58 am

Yeah I have the same problem with my gauges. When I first turned the key on they fluctuate back and forth quite a bit but then the one everything settles down.
I always had the same issue with the term ground. It means different things. For instance with generators where do you ground them?
Same with alternating current versus direct current. As Michelle said the term ground is a little misleading to us normal people. I've always heard the term reference as well. One thing's for sure if those little gremlins don't have a good return path to wherever they came from, things are just not going to work right.

Re: Instrumentation Grounding

Reply #19 – January 09, 2020, 11:04:39 am

Quote from: Bob and Julie – January 09, 2020, 02:46:58 am

Yeah I have the same problem with my gauges. When I first turned the key on they fluctuate back and forth quite a bit but then the one everything settles down.
I always had the same issue with the term ground. It means different things. For instance with generators where do you ground them?
Same with alternating current versus direct current. As Michelle said the term ground is a little misleading to us normal people. I've always heard the term reference as well. One thing's for sure if those little gremlins don't have a good return path to wherever they came from, things are just not going to work right.

Bob
My gauges tac and speedometer needle goes all the way over to the right and back to zero twice when I turn the key on. I was told to let them cycle and stop then turn the key and start the engine. Not sure what it does but that is what I do every time.
Is this what you are talking about?
I would like for someone to explain if I am doing it right and why.
I am needing a lot of training about these coaches.
Thanks

Re: Instrumentation Grounding

Reply #20 – January 09, 2020, 08:24:40 pm

Ron,

I have had my coach for 14 years and I still need a lot of training.

Re: Instrumentation Grounding

Reply #21 – January 09, 2020, 08:25:58 pm

Also, I go through the same starting procedure as you but do not know why.

Re: Instrumentation Grounding

Reply #22 – January 09, 2020, 10:18:45 pm

Quote from: rclark – January 09, 2020, 11:04:39 am

.............My gauges tach and speedometer needle goes all the way over to the right and back to zero twice when I turn the key on. I was told to let them cycle and stop then turn the key and start the engine. Not sure what it does but that is what I do every time.
.............I would like for someone to explain if I am doing it right and why.

Quote from: Jan & Richard – January 09, 2020, 08:25:58 pm

........... I go through the same starting procedure as you but do not know why.

Richard, Ron,

Asked and answered several years ago:

ALWAYS let your Tach and Odometer go through their energization-self-calibration cycles and reach their rest condition prior to moving the ignition key to the start position. Many FT components (OEM) do not have surge suppression diodes that shunt the inductive kick of the starter and starter solenoid when they are released. If your Tach and/or Odometer are mid-stream of their self calibration cycle, they are particularly vulnerable to damage from the surge, that is felt throughout the entire DC system, when you release the starter. Ever wonder why so many SW VDO instruments fail or partially fail in FT's vs SOB's? This is the reason. See the following:

Operating Checklists for Comment and Suggestions

HTH,
Neal

Re: Instrumentation Grounding

Reply #23 – January 09, 2020, 10:53:04 pm

With the exception of the speedometer, that didn't work, none of our gauges cycle when the key is turned prior to start up. Our issue was that the needles on the gauges would jump to different locations when say the lights or dash fan was turned on. It had me bugged because the water temperature gauge for instance would be reading normal but when the lights or fan was turned on the needle would jump up to a very high temperature. I was never sure which one was actually correct. All of the gauges minus the tach would jump around in a similar fashion. I think the incorrectly termed "grounding" straps have solved the issue though.

Re: Instrumentation Grounding

Reply #24 – January 09, 2020, 11:06:52 pm

Quote from: The Soft Boulders – January 09, 2020, 10:53:04 pm

With the exception of the speedometer, that didn't work, none of our gauges cycle when the key is turned prior to start up.

Nor do the gauges in our coach.

I believe the instrument action being discussed above is a characteristic of the newer model coaches with electronic engine controls and gauges. Our older model U280s with mechanical engine controls are less complicated. Apparently our gauges do not require "self calibration".

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