The Sneak Circuit . . . by Jim Becker
What is a sneak circuit? It is an electrical circuit there the electricity decides to go somewhere the designer didnít intend it to. This is not the result of some bad connection, or bare insulation or the like. It is usually the result of the current simply feeding from one part of the circuit to another, usually backwards from the intended direction. The General had one that got some publicity a few years back. I donít have the exact details, but it went something like: Turn the key off, but with the radio switched on. Put on the 4 way flashers then step on the brake pedal. The radio would then go on and off in unison with the flashers. Power from the 4 ways fed backwards through the brake light switch to energize the radio feed.
OK, what does this have to do with our Corvairs? A couple things. One is the potential for problems when we add some of our own electrical accessories to a car. Most of the time you will be OK if you follow a published wiring diagram. But you need to be careful if you go off on your own, especially if you need to tap directly into an unswitched power source. Some of our design-it-yourself air conditioning systems are loaded with opportunities for problems. I canít possibly describe all the ways you can run into these problems. I would recommend that you have a second set of eyes go over the layout of any major rewiring projects.
There are some closely related problems that can show up on your perfectly stock Corvair. Although not literally sneak circuits, the behavior caused by these is similar. A fairly common one involves the headlight or taillight. The symptoms for the headlight: Turn on the lights, on low beam. One low beam is on and looks normal. The other is very dim. Both of the high beam units are also on, but very dim. Switch to high beams. Now both lights on the "good" side are on at normal brightness and both on the other side are still useless. How can this be? The headlights on the bad side have lost their ground. In many cases the whole headlight bucket has lost its ground. When on low beams, the problem low beam unit has power running through it but with the missing ground, the only connection is backwards through the other filament (and the other unit) on through the high beam wires to the other side of the car where it continues through the other high beam unit to ground. At an average of 4 volts each, there isnít much light produced.
A similar problem shows up on taillights. In this case, turning on the lights finds one normal light and one dim one. Step on the brakes and the dim taillight goes out. Again it is a lost ground. On early taillights it is usually a lost ground between the housing and the car body. Sometimes it is the dreaded loss between the socket and the housing. On late models, the problem is frequently caused when the metal socket insert comes loose and backs part way out of the plastic holder. Sometimes the socket can be shoved back in for several more trouble free years, or maybe adding a little bend to the retainer prongs will fix it. Replacing the whole socket is a more permanent solution.
As strange as these behaviors can be, they are nothing compared to the late model instrument panel. The entire instrument panel grounds through a strap that runs to the panel retaining screw at the bottom, to the left of the steering column. If this ground is lost, there is no end to the behavior that can be seen. Between lights, turn signal indicators, gas gauge etc. all sorts of things can happen.
Another area where an overlooked ground problem can cause major grief is in the charging system. Not only do the battery and generator need good grounds, so does the voltage regulator. The regulators all were originally equipped with a ground strap. One end of the strap is positioned so a mounting screw will ground it. Be sure it is in place and has a good connection at each end. It suffices to say, if you see behavior that defies description, check the ground.
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