Crossed wires?


#1

Prompted by the thread on Cougar’s brake light fuse problem, I recall two incidents and pose a query.

First, in Spring 1962 my Dad got a new Plymouth Valiant (slant six; manual transmission, the one where the forks on the linkage would jam from time to time). A few days later the friend following me complained about my driving – “signal right, turn left; and vice versa.” Turns out the rear turn signals were cross-wired.

Second, a few months ago I was following a new small Chevy (I don’t remember the model, but I think it was near the bottom of the line). Every time we neared a stop light his brake lights went off. As we started up, they would come back on. After a couple of cycles, I deduced that they were in reverse-logic. At they next stop I jumped out to tell him. “I know, $*$&^!!” he growled. (“So why don’t you get it fixed,” I wondered, but did NOT say.)

Query: On a '62 Valiant I guess a lot of connections were quick-disconnect types; easy to mis-wire right and left, or normally-open and normally-closed. But it seems that on modern cars everything has a keyed connector plug/socket, and I’d presume that the harnesses are checked at manufacture. So, even if the brake light switch did have a normally-closed contact, how does it get mis-wired? Or is there some other explanation?


#2

It could have been as simple as having the wrong bulbs in the sockets. All it takes sometimes is one wrong bulb to screw things up.


#3

The old cars had keyed connectors, too but the terminals could be installed in reverse order. I.e. The stop lamp filament powered by the running lights and the running to the stop lamp wire.
I had a 64 Pontiac that had one side wired that way. The car was rear ended twice over 13 years before that was discovered.


#4

Some of those kind of switches have both types of contacts. NO, and NC. Never happened to me on cars that I recall, but on electronics projects I’ve had that problem when I hooked up to the wrong set of contacts. Digital logic circuits can do that too. A couple years ago a tradesman doing a project for me showed me his cell phone display. After he dropped it he said everything became right/left reversed so it looked like he was looking at in in a mirror. Still usable otherwise.


#5

I suspect the lights you saw were really the running lights and not the brake lights. If that really is the case then the trouble is most likely due to a faulty ground to the rear lights. The ground connection was good enough for the lower power needed by the running lights to allow them to work but when the brake lights are supposed to work things get worse. The higher current needed by the brake lights would cause a even a larger voltage drop across the bad ground connection and so even less voltage gets to the running lights, enough drop that it causes them to go out also. Bad grounding can cause “what seems to be”, strange science to happen.


#6

Good point @Cougar … loose or missing grounds at the light fixtures in particular can cause this type of problem.


#7

I’ve seen 1157 bulbs forced in backwkwards- thus the wrong filament lit up when energized.

lol