Written by: CHRIS HOWARD mailto:chris@turbovan.com
The headlights on my Datsun 1600 were very poor, not nearly bright enough. The 30+-year-old wiring and standard high beam relay weren't up to the job any more. I set about rewiring my lights and here is what I did.
Stock headlight wiring
The stock Datsun 1600 headlight wiring is a strange setup. Someone had already fiddled with my wiring and installed a couple of extra relays. Here's what I gathered from studying the stock wiring on my '69 and a somewhat dodgy circuit diagram:
Stock headlights are switched on the negative (earth or 0V) side. This means that unlike most cars the headlights have a constant supply of +12V, and the earth wire runs to the stock switches and relay.
The parking lights, tail lights, number plate and instrument lights are all switched on the positive (+12V) side.
The main headlight switch on the dash is two switches in one. One half of the switch switches the earth for the headlights, the other half switches +12V for the other lights.
The dip switch on the column switches a single lead to earth when in the pulled back position.
My rewiring plan
I wanted to completely replace the headlight wiring up to the headlights themselves, and eliminate the stock relay from the circuit entirely. I also had some spotlights which needed to be hooked up. I decided to run each pair of lights on a separate circuit for minimum voltage drop and maximum brightness. To allow for a future upgrade to 90/100W outers and 130W inners I designed a circuit, which would cater for this amount of load.
SEE accompanying JPG image files
Headlight wiring update
Headlight wiring update - no fogs
How it works
The new circuit still uses a switched earth design to activate the relays. This is to minimise the number of changes needed to the original switches and wiring. The relays themselves however switch the conventional positive side of the headlights.
The outer low beam headlights will come on when the stock switch is pulled out to the second position. Outers will switch to high beam and inners will come on when the dip switch is pulled back. Spotlights will also come on with the dip switch if the spotlight switch is on. The high beam and spotlight relay positive switch feeds are taken from the outer relay output. This ensures that high beams and spotlights turn off regardless of the dip switch position if you switch the main switch off.
Relays
For the 3 main relays I used Hella relays with built in 25amp blade fuse. These are really neat and make for a more compact installation, as you don't need to use any in-line fuse holders. I couldn't find them in the local parts places so I ordered them from http://www.autospeed.com" onclick="window.open(this.href);return false; There is a diagram on the side of the relay so you can work out which pin is which, pins 85 and 86 are for the coil, pin 30 is +12v and pin 87 is the output.
If you don't use relays with an in-built fuse holder, get some in-line fuse holders and put them between the battery and each relay.
The switchover relay is needed to switch the outer lights from the low to high beam filament. I sourced this from http://www.jaycar.com.au" onclick="window.open(this.href);return false; , part no SY-4070.
Wire
For the thick wires as shown on the diagram, use wire rated at 20 amps or higher. The thin wires can be much thinner as they will only flow a couple of hundred milliamps to drive the relays.
Installing
I mounted the new relays on a piece of folded sheet steel on the driver's side near the battery. Being close to the battery is good as it gives the shortest cable runs and hence least voltage drop. Run new wires from the relay panel to both headlights. Make sure you secure the wires running from one side of the car to the other with some cable ties, you don't want to get them caught in the engine fan.
Connecting it up
I soldered each join to the factory loom and used heat shrink to cover the joins. You can use crimp connectors if you don't have a soldering iron. Use crimp connectors for the relay connections. Test each crimp connector by trying to pull the wire out, ratchet type crimpers work best.
Spot lights
Starting with the easiest, connect the positive output from the relay to the spotlights. The spotlights will probably earth through their own mounts, but you may need to run an earth wire.
Inner beams
If you look at the headlight plugs, you will see that the inner headlights are connected directly to the outer headlights. In the stock setup they both run from the same circuit. This setup will give them separate circuits, so you can cut both these wires close to the outer beam. Connect one of the wires (either one) to a good earth nearby. Connect the other wire to the inner beam relay output as shown in the diagram.
Outer beams
The outer beam plug has three wires. One is for the low beam filament, one is for the high beam filament, and one is common. The one wire which did not run to the inners is the low beam, connect this to the switchover relay as shown in the diagram. On my car the red wire with no trace was the ground wire. You can identify this before you start by measuring which pin has close to 0V with the headlights turned on. Connect the ground wire to a good earth nearby. Connect the remaining wire to the switchover relay output as shown in the diagram.
Headlight switch
Unscrew the headlight switch from the dash and have a look on the back of the switch. There are a number of terminals with wires soldered onto them. Now you need to locate the pin which is switched to ground only when the switch is pulled out to the second position (we only want parking lights on in the first position). This is the middle contact closest to the switch plunger, you can verify by measuring resistance to earth with a multimeter if you wish. Cut the wire leading to this contact, this becomes your main light switch wire as show in the diagram. Ignore all the other wires, they are for your parking and illumination lights which will be unaffected.
Dip Switch
The dip switch wiring emerges near the ignition key in a square shaped plug. The black and red wire is for the dip switch. Cut this wire and it becomes your dip switch feed as show on the diagram. You can then solder a new wire onto the dip switch wire and run it to your relay panel.
Spotlight switch wire
Find a suitable spot to mount your spotlight switch and wire it up as shown.
Routing the wires
Unscrew the fuse box and feed the wires through the existing rubber grommet. You can then feed them through the passage where the bonnet cable runs. This emerges right near where you will mount the relay panel so makes the wiring quite neat.
Finishing up
You can now remove the stock headlight relay, it is on the strut tower near the fusebox, closest to the engine. Cover the plug with insulation tape. Also tape up the ends of the stock wires that are no longer used.
Variations
If you don't want to go as far as I did, you can use only two relays and wire the inners straight to the outers as per the stock setup. Just ignore the inner beam wiring on the diagram and wire up the rest as shown. Make sure the relays you use are rated at least to the total load your lights will draw.
Disclaimer
Please don't blame me if your setup differs and you blow things up! Send me an email if you have any questions
ALL CREDIT GOES TO: CHRIS HOWARD
