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Automotive/'89 Chevy Cheyenne Amp Gauge

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Expert: - 1/31/2008


Question
While fixing several of the "little" things on my recent work truck purchase, I can't seem to make heads or tails on why the amp gauge isn't working.  I found the problem with the oil gauge (the sending unit). I'd love to know if it's something that can be repaired.  I'd hate to have to replace the entire cluster, as they're hard to find around these parts.

Answer
Interestingly enough, I am myself in the process of replacing the entire instrument cluster in my Ford van with a custom new one of my own design - all in order to solve a few problems including that of an errant and not-well-calibrated amp gauge, as well as to house a set of new and additional instruments in one ergonomically-correct package that will be a vast improvement over the various pod-mounted instruments it will replace.

Automotive amp gauges usually are driven by current division, wherein the meter and the leads connecting to it are in parallel with a defined length of the main feeder between the battery and the main point of connection on the power bus.  The resistance of the main feeder is an order of magnitude or two lower than that of the connecting wires to the meter and the meter itself, but the ratio between those two resistances is set so that, whatever current flows on the main bus, a proportionally small sample of that current flows through the meter.  The meter scale (if present) is calibrated so that, when "Current_Bus / ratio" current flows through the meter, the meter will read the value of "Current_Bus".

The usual problem that occurs with such systems is one where the linking connection opens, or its resistance goes up due to a bad connector (most often) or a damaged wire (sometimes).

Anyway, the above is general.  I do not have the specific data for your 89 Cheyenne, but I can probably get some information from an auto-electric professional friend who does a lot with Chevy trucks.  Whatever he can provide, I shall get back to you.

Cheers ... EGK

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Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

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