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Datsun 620 DRL/automatic headlights mod

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So, after the 3rd episode of dead battery blues (yes, my fault for leaving the headlight switch on...), I decided to wire the headlights to come on with the key. Not a difficult mod, just requires a little hacking, soldering, and screwing 🙂.

Looking at the fuse panel on my 78 620, all the fuses on the right are hot while the fuses on the left are tied to the ignition. 



1. Remove fuse panel and disconnect wiring harnesses. Remove the fuses too. Note the view from the backside means the hot fuses are now on the left.



2. Remove the HOT bus from the plastic housing with needle nose pliers. Just squeeze each fuse terminal and it pops right out. Use your preferred cutting tool (dremel for me) to hack the bus above the bottom fuse location.



3. Solder a 12V relay in place. I used this one from Radioshack for $5. Solder the relay outputs to the buss pieces that were cut before reinserting into the housing. Otherwise you'll melt the plastic housing 🙂. This is pins 87 and 30 for this relay - polarity doesn't matter. I used black for the output wires, and white for the control wires. Reinstall buss in housing. It should look like below



4. Screw the fuse panel back into the truck and connect the control wires (pins 85 and 86). Again, polarity doesn't matter. One end goes to ground, the other to a switched 12V source. I screwed the GND wire to the mounting bracket for the fuse panel as shown below:



5. Connect the second lead to a switched 12V source. I spliced into the radio wire because it was easy to find. It's the blue one  just to the right of the image above. 



6. Add a cable tie to tidy things up, and you're done. 


Voila, now the headlights only come on when the key is on. No more dead batteries!

I leave my headlight switch on all the time now. Might as well have them on during the day for visibility. For those concerned about the additional current draw when starting, the radio wire is actually off when the key is in the "start" position, so the headlights aren't drawing juice when the starter is going. The turn on as soon as the key springs back to "run". 


Why use a relay instead of simply running a wire from the switched (left) side of the fuse panel to the headlight/parking bus you ask? This would put more load on the wire powering the switched side of the fuse panel, and I was worried about the wire being too small to handle the additional current. Using a relay means the current for the lights is still on the original power wire, so no worries about frying any wires.

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Well done!


I've toyed with this idea. My 710 has relays one for each side that I added so wouldn't take much for this. I drive with the lamps on because I'm afraid some dick driving a Prius will glance in my direction and NOT seeing any headlights (that all cars have today) will pull out in front of me..

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