95 E150 4.9 I noticed my coolant gauge fluctuating and abnormally high then I noticed my oil pressure really high. When I give it gas from a stop the oil gauge goes all the way up and the coolant gauge moves a quarter inch in either direction.
The charging and gas gauge seem to be normal, charging gauge may be slightly low.
first of all, econoline gages are notoriously inaccurate.
second, there is a component called the "instrument voltage regulator" mounted on the back of the instrument cluster, and when it fails, it usually causes the temp, oil, and fuel gages to all spike together. a problem with it WILL cause the 3 gages to make similar changes at the same time, usually in the form of excessively high readings.
you may also want to attach a voltmeter to the system to determine if your charging system is putting out too much voltage. the easiest way to set this up is to use a little guy like 12 Volt Battery/Alternator Tester , just plug it in and drive. i use mine all the time on various systems, its simple and reliable.
The ground to the body (10GA wire) from the NEG battery post is the one you to make sure is a good ground for the cluster.
I found this post in a search. Same symptoms on my 95 E250. Found a couple of other posts on the internet with the same symptoms on E series. No answers, so......Turned out the ~4GA main engine/battery ground buried under the alternator was not tight. Cleaned it up and problems went away!
I spent a lot of time with wiring diagrams, other grounds and checking voltages but the main battery engine ground was the culprit. This ground is very hard to get at since it is buried back from the front right lower engine block corner......