Text and Illustration by Bruce Godfrey

Some years ago, I met a guy at a 510 parts garage sale who was trying to figure out how to rig up a dual-filament bulb socket for his side-marker lights. He told me a story about a wreck he was in which resulted in his car being totaled, and that could have been avoided if his turn signals had been visible from the side. He was in the process of building a new Dime with the insurance money and he wanted to include this feature. Having signals visible from the side can make a difference in heavy traffic. Also, when you are at an intersection, folks approaching from the right or left generally can not see your front signals until they are nearly in front of you. Same thing when you try to pull out of a parking lot onto the street. At the time, I could not think of an easy way to rig the side-marker lights to blink. Then I joined the bluebirds e-mail listserv. I posed the question to the list, and Thomas Walter, an electrical engineer, responded. Turned out Tom worked a few buildings over from me, so we met in the parking lot after work one day and he told me about the way GM cars are wired so that the side marker lights blink.

It was very simple—they just wired the ground side of the side marker light to the hot side of the turn-signal filament of the front signal/parking light. This way, when the turn-signal filament of the front dual-filament bulb is off, the side marker light finds ground through that filament. So with just the parking lights on, things are as they normally are with the side marker light, just with a longer path to ground. When the turn signal on that side is activated, then during its “on” phase, the side marker light gets 12 V at both sides of the filament. So no net current flows, and it is turned off. When the signal blinks off, current flows through the marker filament, then through the dual filament to ground, and the side marker light blinks back on. You see the same thing happen on most American cars—the side-marker light blinks as a turn signal, but out of phase with the front turn signal.

It wasn't my top priority project so I didn't get right on it. I would have had to stick multitester leads into all the connectors up by the lights, walk around the car and flip switches, then walk back to the tester to see what was hot and what was not. Kind of a lot of trouble. But now I have the DAMB Productions wiring diagram, so I had a look at it to see what it would take to make this change to the wiring. Not much, as it turns out. No clipping connectors off the harness or soldering on new ones. All I had to do was buy some bullet-style crimp connectors and make a little splice with a few inches of wire. Takes maybe a minute to install, or remove and put everything back in stock form.

There is a very good possibility, however, that the screws which mount the side-marker light to the fender could ground the front blinker hot side—a dead short and a blown fuse, in other words. This is easily avoided by picking up four 8x32 nylon screws, maybe an inch long, and nuts from your local hardware store. Datsun used a ground wire on the body of the side-marker light fixture because the holes don't always line up well enough for a good ground from the reflector to the fender through the screw (but sometimes they do). Your blinker circuit runs through your hazard-flasher switch, so if the fuse doesn't blow soon enough you could weld up some terminals in that switch. They cost $16 wholesale these days, which would increase the cost of this operation by a factor of four or so!

One final note - Your factory signal-flasher unit is current sensitive, using a bimetal strip which heats up as current flows through it until it gets hot enough to bend away from its contact and break the circuit. More current flowing (i.e. more light bulbs in the circuit), and it will heat up faster and blink much faster. Mine burned out after about a month of this. I replaced it with an electronic flasher (Littlefuse ELF102, about $7.00) and now the signals always blink at a perfectly controlled rate. That's better than they ever did before.