Automotive/Dashboard lights

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Expert: - 1/2/2009


Question
My 79 mark v dashboard lights, after driving awaile, blink off for about 20 seconds then come back on. It then continues to happen about every 30 seconds. Thank you

Answer
It would appear that the dashlight circuit is protected by an auto-reset thermal circuit breaker, and that this begins to cycle after a period of time, due to becoming overly warm.

The nature of the problem - delayed initial onset followed by fairly long repetition period - suggests that the issue is likely with the circuit breaker itself rather than due to any real fault in the dash lighting circuit, with one exception, noted further below.  

The most likely problem causing this breaker to cycle is that it is running overly warm due to excess resistance that has developed, over either its interrupting contacts or over its terminals by which it connects to its mounting block socket or harness connector.  Oxidised or pitted contacts or an oxidised or loose connector both cause increased resistance at those points causing, in turn, excess heating which would have the ultimate consequence of heating the CB to its trip point.  (Ford headlight switches of that era had internal integral circuit breakers, and often developed cycling problems as the switch aged, causing the headlights to cycle on and off.  I solved such problems by upgrading the circuit to include headlight relays so as to take the direct headlight load off the switch.)

The fix could be as simple as disconnecting the breaker, and cleaning and greasing both its terminals and those of its mating socket.  Try this and see if it ends the problem - that would address a terminal issue.  If it does not, the next step could be to replace the CB itself - that would address a pitted contact issue.

Before doing either, however, check your service history.  Is it possible that some instrument lamps were replaced in the last while, possible with brighter ones, drawing more current?  Similarly, has there been any significant additions of after-market gauges, adding extra lighting load?

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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