MCI & Bad Grounding - Tech Notes

[Hartley]

The other week I was trying to help a buddy with his shutdown
issues. His engine wouldn't shut down from front or back.

Well..

As the story unfolded, After days of fiddling in the rear junction box chasing
phantoms ( gremlins ! ) .. The problem continued....

An offhand mention of a relay problem with the master switch up front got me to thinking and then the gremlins moved up front into the side panel junction box.

The short end of this story is simple..

If your dash board is acting wierd..
If your switches seem wierd..
If you get phantom problems with telltale lamps...
If your gauges all read wierd or in error or not at all...

FIX the GROUNDS - FIRST!!!!

MCI as well as others?? Seemed to think that putting brass screws into sheets
of aluminum was the proper way to build a grounding buss bar.

NOT ! -- If the studs are loose or simply pop off then they are losing contact
with the grounding buss bar or plate. ( ground wires on studs should be tight and not move at all. )

Take the alumimum out and replace it with a copper or brass plate and install a known good set of grounding lugs/screws. Always run extra #10 wires to dash board panels down to a verifiable ground bolt or stud that you have tested to
have a 100% solid connection to the chassis ground and battery ground...

Magically the run/stop problem went away and all the gauges now work and no more funky indicators and goofy switches.

All due to bad grounds up front in the drivers junction box area...

Dave....

[johns4104s]

Dave,

Drivers area, are you pointing to the panel on the outside under the driver?

Thanks

John

[Busted Knuckle]

Dave,

Drivers area, are you pointing to the panel on the outside under the driver?

Thanks

John

yes

[bevans6]

With reference to another thread about dielectric spray and grease, I bet a product like Corrosion-X would help a lot on the stud panel inside the junction box, and protecting the grounds and buss bars.

Brian

[Hartley]

The dielectric coating would work fine.. After you checked and verified
that all of the connections are solid and working.

The main problem seems to be in using dissimilar metals and the propensity
for electrical boxes and connections to gain extra moisture even from the air itself.

For instance, You will never find aluminum and copper, brass or steel mixed on aircraft electrical systems without some serious preparation to minimize corrosion.
The same holds true for military hardware.

There are fasteners made to make solid connections between differing metals that have treatments to insure good connections.

The sad part is that I have never seen these used correctly on any MCI or for that matter many buses. There's always a gotcha usually hidden up in some junction box or panel. My MC9 has everything mounted on a sheet of aluminum
inside the drivers outside electrial panel. The problem is that the ground attachments are to the panel itself. The problem is that the pop-rivets that hold the panel to the frame get loose over time. And the grounding becomes weak or intermittant. Same for the dash panel inserts. They are just weak grounds and the only way to solve the gremlin problem is running new ground wires to a known good attach point. I spent 3 weeks trying to fix my temp gauge because the readings changed 20 degrees when I turned on the headlights.

It was bad grounds the whole time.

These buses have lots of wires that depend on closed loops from 40 feet away to make stuff work right. Having poor connections just makes you a bit crazier than normal. Then you get an electronic chassis or engine system thrown into the mix and all bets are off and you have to go back to the basics of connection quality.

I just hope that if anyone reads this that they get some solace from the fact that equipment grounds if checked first may be the answer.

The quality of the electrical diagrams leaves a lot of information out or is so confusing that even after 40+ years of doing wiring and electronics that I even get frustrated. It would be my guess that most manuals have little relevant correct information especially in the diagram departments. Those "option" notes don't seem to get copied along with a schematics so we all have to learn to work through the missing information.

I would imagine that the manufacturer purposely leaves out the real diagrams so the customer has to come to their service center to get stuff fixed. They don't work from poor photocopies usually.

Generally we (busnuts) usually don't use but about 40% of the original wiring mainly to operate engines & lights. The other 60% is there just to cause confusion when stuff goes wrong. So the question you have to ask yourself is whether to rip out all of the wiring and put in just what is needed or risk problems later and hope there are enough spare wires in the harness to keep stuff working.

Two schools - No Teachers .... DUH....

[Len Silva]

Dave,

I agree completely.  Having spent my working life in telecommunications and very high current DC circuits, you cannot emphasize enough, the necessity for good ground connections.  The product of choice is "No-Ox by Sanchem http://www.sanchem.com/aSpecialE.html .
We used copper wire with aluminum crimp connectors, copper bus, brass or stainless bolts in any combination with no problems using this stuff.  It should also be used between the wire and the connector.

Here is a company that can provide the No-Ox, copper ground bars, preterminated cable to order, etc..  http://stormcopperstore.com/no-ox-id-a.html?gclid=CNb0xNGts54CFRQhnAod337jmg

The 4104 had a large ground cable that ran the length of the bus, connected to copper bus bars in every panel or junction.  I guess it is too expensive to use on modern buses.

[PCC]

I rely on "overkill" to make sure that the electrical connections are secure.

Len, I also worked in telecommunications, and I recall the many times a simple 'sometimes-good' connection was responsible for troubles. They took centuries to find !

I try to make those ground connections as idiot-proof as possible, because it is too easy to test good with a meter, and still have a bad connection.

[Len Silva]

If you have ever had occasion to get in your car and the lights come on and work fine until you hit the starter, then everything goes dead.
Get out and "jiggle the battery terminals" and it may or may not start right up.

That is oxidation at work.

Connections can seem to be good one minute and bad the next, or they are good until a heavy load is put on them, then they go open.  If the bad connection is on the positive side, it is usually just one circuit or device that fail.  If it is on the ground side, it can result in all kings of strange behavious.