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Saturday, June 2, 2018

Grounded

We had such great plans for today, but the weather had other ideas.  It is so incredibly windy we cannot open the garage door.  Therefore, rolling KITT outside is out of the question.  We had planned to clean the garage floor and needed to be able to move KITT outside to do that.  Since we could not, we tackled a couple of items from our What's Next list instead.

After installing the digital gauges in KARR, I noticed the temperature gauge and fuel gauge were erratic in their readings.  This could be one or more of three things: 1) the gauges are bad; 2) there is a grounding issue; or 3) the sending units are bad.  I know the temperature sending unit is not bad because I just replaced it.  I am going to operate on the assumption that the fuel sending unit is also not bad as it was working prior to installing the digital gauges.  Therefore, I am left with either a grounding issue or the gauges are bad.

To get started, I needed to remove the back cover of the gauge cluster to get at the wiring.





Next I inspected and checked the ground wires and connections.




Then I hooked up a test lead to the ground contact point for the temperature and fuel gauges.  This allowed me to ground that contact point to a known good ground in the car.


Starting KARR with the gauges grounded.


Next I grabbed my ALDL to Bluetooth scanning tool so I could hook it up to KARR's diagnostic port.  I had to remove the center console cigarette lighter cover to access the port, and noticed my repair job on my cracked cover finally gave out.  You can see the piece in the picture below.  I will have to order a new cover.  I have KARR's scanner override switch mounted to this cover, so I will have to move that.  


The ALDL to Bluetooth scanning tool allows me to view the information from KARR's onboard computer on my Android phone.  We verified the gauge readings were consistent with what the computer was showing, and they were very close.  This is looking very much like just a grounding issue.



One last thing to do was to eliminate the gauges as being bad.  I ordered a test lead specifically for the temperature sending unit from Rodney Dickman's Fiero Store.  The test lead allows you to test both the minimum and maximum readings on the gauge by utilizing the proper resistive load.  I did this both with the ground test lead attached and without.  With the ground lead attached the gauges worked as expected.  Without the ground lead attached the readings were intermittent.  This is definitely a grounding issue.


I checked the continuity between the ground wire in the connector that provides the ground for the flexible PCB on the back of the gauges and the ground contact point for the temperature and fuel sending unit.  It was showing mild resistance.


I decided to clean the contact points on the connector.  This lessened the resistance but did not eliminate it.


I decided to tap into another ground wire for the gauges and connect it directly to the ground contact point for the temperature and fuel sending unit.


Once I was finished I reinstalled the back cover of the gauge cluster.  We did a quick test drive to pick up a pizza and so far the results look very promising.


Next on our list was mounting our old 32" TV to the garage wall on a 24" extension arm.  (Sara made me return the 75" TV I was originally going to put in the garage.)  With the added Chromecast, I think the TV will be invaluable for pulling up pictures, videos, and...





Watching Knight Rider!


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