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520 4-headlight lights. Which ones?


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I would think the fusebox in a 520 is similar to the one in a 521.  Adequate, when new, for a stock electrical system.  Adding headlihgts that can take H4 lamps will probably be more than the stock 45 year old fusebox can handle.

 

Stock headlights, on high beam, two 50 watt lamps, two 37.5 watt lamps.  175 watts total.  Nominal current, 14.6 amps.   

H4 lamps, on high beam, two 55 watt lamps, two 60 watt lamps, 230 watt total.  Nominal current, 19.2 amps.

 

Additionally, stock 520 trucks have a 35 amp alternator.  Not a lot of reserve capacity to run heater fan, wipers, smaller lamps, and the trucks ignition system.  But you can live with a 35 amp alternator, if you do not drive with high beams much.

 

H4 lamps like to get their full rated voltage. 

 

This is the path the electricity takes in a stock 521, to get from the battery, and back to the battery.   Battery positive, to fusebox.  In the fusebox, through the fuse clips, into the fuse, back out of the fuse, a second set of clips, and a slip on spade connector.   Every one of these connections to the fuse has a little resistance, and creates heat.  Every one of these connections possibly has 45 years of corrosion, or oxidation, that adds resistance.  If the clips ever got hot, they lose spring tension, and the connection gets worse.  There are lots of 521 fuse boxes that have the headlight fuse terminals literally melted out of the plastic.

 

From there, a thick red wire carries headlight current into the cab, it goes through a connector by the glove box, into the cab, or dashboard wire harness, through another connector, into the light switch, back out the light switch, the switch connector, and into a thick red with yellow stripe wire, back to another connector, by the glove box, and back into the engine room wire harness.  Then the red with yellow stripe wire goes to the headlight relay. 

 

The headlight relay then applies the headlight power to either the red with black wire, low beams, or the red with white wire, high beams.  These red with black or white wires have a "Y" to either side of the truck, and "Y" again for the high beams only.  Power after the headlights is on a black ground wire that has three "Y"s again to one thick black wire, and this black wire goes to the voltage regulator mounting bolt, and joins another black wire that goes to the alternator frame.  the alternator frame has a third black wire that goes to the negative battery cable.

 

A 521 has the stock headlight relay by the battery.  The stock 521 headlight relay conveniently uses 1/4 spade connectors.  So do Bosch "cube relays. 

You can take a single Bosch cube relay, mount it by the stock relay.  Move the red with yellow stripe wire from the stock headlight relay to pin 86 of the Bosch relay.  Ground pin 85 of the Bosch relay.  Now the headlight switch turn the Bosch relay on, but instead of 15 amps of headlight current going through the fusebox, and headlight switch, and connections, a few tenths of an amp of relay trigger current goes that way.

Get battery FUSED power from the starter lug, or the wire that goes to the fusebox, like this.  It is the orange wire, with the fuse holder.

NewRelayB.jpg

Run that power wire to pin 30 of the Bosch relay you added.

 

Now, make a short jumper wire from pin 87 of the Bosch relay, to the empty pin on the original Datsun 521 headlight relay.

 

Here is a 521 electrical diagram, with most of everything edited out, except for the headlight circuit.

HeadlightWires.jpg

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Adding headlihgts that can take H4 lamps will probably be more than the stock 45 year old fusebox can handle.

 

 

Thanks for the detailed response.  I am intimately familiar with Bosch-style relays... I actually wrote a small pamphlet/book on their use about 25 years ago that was published in a DIY electronics series sold at electronics hobbyist stores.  I'll see if I can find a copy in my boxes-o-junk to scan and post (maybe I should check the copyright first... I don't own those... I'm just the author).

 

The 520 and 521 fuse boxes are very similar, though based on the info I have, the circuits are slightly different (mostly trivial differences).  When I got the truck, I created a wall poster-sized schematic from info I found online, in the truck's owner's manual, and tracing a few wires. 

 

My original question was simply to clarify what LOOKED LIKE 5001/5006 bulbs, but might not have been... since I couldn't do a simple lookup for them at Rockauto, Autozone, or even at NAPA.  They just weren't listed... so it gave me the impression they might be something oddball instead of then-industry-standard bulbs.  Sounds like they aren't oddball... and those parts catalogs just didn't bother to fill in the info (though, I looked up... as an example... 1968 Pontiac Firebird (which I know uses 5001/5006 headlights), and they ARE listed).  Anyway... thanks, all, for the info.

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Since when I was putting my project Ratsun together, I just used headlamps that worked, for testing purposes, one low beam burned out rather quickly.

My local auto parts store had a General Electric H5006 lamp, 35/50 watt, halogen sealed beam head lamp.  The ultimate lamp is a Cibie 5 3/4 lamp, and uses the H4 halogen bulbs.  They also make a high beam only lamp, that has a metal housing.  You have to be aware of the polarity on the headlamp plug, since the metal housing is grounded.

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