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Automotive/instrument cluster fuse bolws everytime the car is started

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Expert: - 4/18/2009


Question
I have a 3.8L V6 03 Pajero The intrusment cluster fuse blows everytime the car is started relusting in no electric windows, no fuel or temp gauge, no speedo or odometer or blinkers. Any ideads would be great

Answer
It is a little surprising to hear that any fuse or (more likely) fuses protecting the instrumentation would also protect the circuits for the hazard warning lights ("blinkers"?) and the power windows!  Are you really sure that the problem is, in fact, a fuse problem?  I do presume that you are replacing the instrument cluster fuse each time this happens, inasmuch as you specifically mention that fuse.  However, the problem does sound a little broader-based than that.

I wonder if the opening of the instrument cluster fuse, if that is happening, might not be a collateral effect of another problem, that problem being a transient perhaps produced by arcing at a bad connection at some point on the accessory bus.  In most cars, this bus will supply power to the fuse block that powers many of the cabin circuits, including instruments and controls, although apparently not the ignition and starter control circuits.  It could be that transient voltages produced by this arcing or related current interrupting action is sufficient to take out smaller-valued fuses.

This is purely conjecture from this great distance but, in the absence of visually finding any obvious short circuits or burned insulation under or behind the instrument panel, having someone with good trouble-shooting skills do a point-to-point visual and resistance check of each portion of the supply run from the fuse block back to its ultimate point of connection at the main bus connections at the battery or main terminal on the line side of the starting contactor would be in order.

That resistance check - properly done using a multimeter having a very low ohms range (capable of measuring to two places of decimal or more - usually found as an auxiliary function on insulation testers such as the Fluke 1520) - is important, because connection problems usually lie at the very interface between contact surfaces, and not be readily visible without dismantling the connection.  Look also for connectors that look like they may have been running a bit warm; discoloured or wrinkled insulation may be a clue here.  Excessive heating is the hallmark of excessive resistance.

Good luck ... 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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