I finally hooked up the battery in my reassembly of the coupe and noticed that even with the doors not put back on, the courtesy lights did not light up. Checked the fuse box and sure enough; there was a blown fuse. When that occurs, resist the temptation to just stuff in another fuse because if there is something amiss, you get another blown fuse. Since I wired my car with a wire harness that takes those mini plastic fuses, I cut apart the blown fuse and soldered wires to the blade ends with a scrounged up side marker light hooked in series and plugged that in in place of the fuse. With a short circuit, the light will light up. There is no fear of the wiring harness going up in smoke because the light provides a load in the circuit. Then it is simply a matter of looking over the circuit in question to see if anything is wrong and unplugging things. When the light goes out, the last thing you did is where the fault lies.
I have used that method and back in my working days I had several “ jumper “ wires with circuit breakers of different amps wired in. I would just power up the circuit with a similar amp or slightly smaller amp jumper wire and start my search! Back then I could actually hear the circuit breaker “ clicking “ so I didn’t have to keep my eyes on the bulb. Sometimes I was twenty feet or more from the fuse box! Won’t work for me anymore…..I can’t hear the clicking anymore! Bones
If you have about 3-4 yards of wire soldered across the ends of a dead fuse, you can hang the light bulb under the hood, in the trunk, etc, so you can see when it goes out.
I have used both the light bulb and circuit breaker . I like the light bulb method as I’m as deaf as a post and can’t hear a damn thing !! And after I got the covid I ended up with tinnitus in my left ear ! Yaaaa ! anyways I got a 12, 24 , 36, 48 volt bulb jumpers to use at work. They work great .
I have been using the bulb method for many years after reading about it. Now I have just wondered if you could use a Piezo buzzer instead of a bulb you would at least hear it without checking if the bulb was liteup as my hearing is not so good
Downside with that is that a piezo buzzer can work at a quite low voltage & current. On a light bulb you get a dim light for little current (as may be normal with other items still working in the circuit) and a bright light for a full short circuit. A buzzer may give you the same sound for both alternatives. May wotk if you can disconnect all loads on that circuit so the constant current when there is no fault is zero, somtimes easy to do, sometimes not.
Makes me think that an oscillator circuit measuring resistance to change the pitch of the tone might work in this case.
That's a current limiter, it limits the amount of current through that particular circuit to whatever current the light bulb can flow. I made up a similar current limiting power source for doing my tube guitar amp work, I always use it when firing up a new amp, it uses an incandescent 110v light bulb to limit the current into the amp. On a normal start up you'll get a flash of light when first turning the amp On, that's the inrush current charging up the filter caps. That only lasts a fraction of a second, then the bulb should settle down into a light glow as the filaments warm up the tubes. If the light remains bright you have a wiring problem somewhere. Looks like this one in this photo I found on the net:
Lots of good tips.. I’ll add one. If you have a blown fuse issue that you cannot find.. turn off the garage lights and in the dark , push the fuse in. When it blows the area of the short will light up like a flash bulb.
Time for an update. I tend to overcomplicate my wiring. This is the circuit that has those courtesy lights that come on when you open the doors. I also added a toggle switch into this so that I could shut them off if I needed to keep the doors open for a long time. Flicked that switch and my test light went out. For the most part, finding electrical faults is easy. The one that had me going nuts involved an aftermarket harness that used a black wire to feed a circuit. I've always assumed that there was an unwritten rule that said all black wires are ground wires.
The thing about unwritten rules is that there's always some people who don't follow them. If you have the joy to work on chinese scooters (or Honda twowheelers from where they seem to have copied the wire colors) you'll find that ground usually is green, battery positive is red to the ignition switch, but battery positive after the ignition switch is black. No doubt confuses a lot of people. You always want to take a look at the schematics before diving too deep into electrical problems, you need to know how the system is built to know how to search for the problem efficiently.
I used to use old headlight warning chimes or key in ignition chime or even seat belt warning light chimes from GM cars. No noise no problem!
That's a great idea to have a visual indicator, so you don't have to keep jumping back and forth to check with a meter. I've often troubleshot wiring by pulling all the fuses, and use a volt meter or test light from line side to load side on each fuse holder. If the volt meter reads voltage there's a draw on the circuit. Then you just have to figure out where the fault in in that circuit.
The Jalopy Journal
