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Automotive/Brake light out on 1998 VW Passat

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Expert: - 10/5/2007


Question
Hi there,

I have the passenger side brake light not working on my 98 Passat (driver's side brake light works OK).  I have tried replacing the bulb with a new one (no luck), with other bulbs from that cluster (eg. tail light/signal light) that are known good and working, with no luck either.  Have checked the fuses to see if there was perhaps a separate fuse for passenger vs. driver's side lights, but there only appears to be 1 fuse for brake lights and it's fine.  The only thing I can think of to try next would be to check the rest of the lights on the passenger side (in case they are somehow related to the problem at hand, although the fuse only mentions "brake lights" on that circuit) and then, of course, wiring.  Might you have any other ideas on troubleshooting this?

thanks,
Loren


Answer
You have pretty much described the systematic process one might reasonably use to hunt down the source of the problem.  Checking out the other lights in the cluster - as you suggest, if you have not already done so - is a good idea as the all-lights-out situation would serve to identify the problem as a bad connection from the entire luminaire assembly to the body or chassis, that being the system "ground".  

That type of problem could be due to a broken ground wire, or due to corrosion build-up between the assembly and its mount; the latter usually is easy to fix by dismantling, cleaning using contact cleaner and emery cloth, and applying electrical connector grease to the joints before reassembling.

The absence of a brake light on one side and not on the other can also indicate a problem with or at the turn signal switch with those vehicles which share the brake lights with the turn signals - usually older cars and light trucks.  Your Passat probably uses amber turn signal lamps, separate from the brake lamps, as do most European cars but, if it does not, I would check this out.

Beyond that, my only remaining suggestion is that, if you had the wiring diagram (and please note that I have these only for my own three vehicles), you would save some time by virtue of having the key to the colour codes for the wire or wires of interest, along with the location of any harness connectors.  Harness connectors also bear checking and servicing for contact corrosion problems.

Having a multimeter (volt-ohm-milliammeter - mainly digital these days) would be handy for doing wire by wire continuity checks.  Basic meters are cheap.

Whatever the specific problem is and wherever it lies, it will turn out to be a simple problem that needs only to be found.  Starting with the obvious - which you have already done - and then working systematically deeper will lead you to the problem and its solution.

Happy hunting ... 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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