Headlight Relays in my 521

[jrock4224]

Wanting a quick diagram on wiring up my headlights with a couple 30 amp relays ....... My 521 is running 55 w bulbs and pops the circuit if I hit high beams after about two minutes

[ggzilla]

You got something broken there. The stock headlights are 50W ... and 60W are normally OK with stock wiring.

 

Here's one way how to do it.

[DanielC]

There is a quick and easy way to add a relay to a 521.

Get a 30 amp relay, and wire it like this.  Take the red with yellow wire off the stock 521 headlight relay, and put it on pin 85 of the new relay.  Ground pin 86 of the new relay.  Run a short 12 gauge wire jumper from pin 87 of the new relay to where the red with yellow wire was.

Run a new FUSED power wire from pin 30 of the new relay to battery plus, or the main wire going into the fuse box, or down to the lug on the starter that the big battery cable is connected to.

This is a picture of the new power wire that goes to pin 30 of the extra relay, the orange wire, with the fuse.

Here is where the extra relay is mounted, next to the stock headlight relay.

 

Post 33, on this page of my project thrad gives a few more details.

http://community.ratsun.net/topic/30606-my-ratsun-datsun-521/page-2

[ggzilla]

I don't follow how this works

 

> This additional relay takes headlight power out of the stock 521 fuse box.

 

Do you mean it takes power from the same terminal as power into the fuse box? And how is it hooked up to the headlights?

[DanielC]

In the first picture, big white wire comes directly from the battery.  Orange wire, with fuse holder goes to new relay.  Orange wire is connected at fusebox, but it does not draw power through fusebox.   Power from the extra relay goes to the original 521 headlight relay, where the power did come from the headlight switch.

 

On an unmodified 521, the second fuse from the inside is the headlight fuse.  It has a dirty thick red wire, at the top of the fusebox in the picture.  This wire goes into the cab, to the headlight switch.   Switched headlight power comes back into the engine compartment on a red with a yellow stripe wire, and goes to the original headlight relay.  Inside the four terminal headlight relay, power is applied to a single pole double throw switch, and the relay coil.   If the headlight relay was a Bosch numbered relay, power is applied to pin 30, and jumped to pin 86.  The normally closed 521 relay contacts go to the low beam headlights from the relay on red with a black stripe wire. In Bosch speak, pin 87A  When you move the high/low switch on the turn signal stalk, the 521 relay coil is grounded, Pin 86 in Bosch, and power is switched to the terminal with the red with white stripe wire, again in Bosch, pin 87, and that wire goes to all four high beam headlights.  

After the headlights, the headlight power goes into a black wire, that goes back to one of the voltage regulator mounting screws.   There is a second black wire there, that goes from the voltage regulator, to the frame of the alternator, and from the alternator frame, another black wire goes to the negative battery cable, bolted to the cylinder head, by the fuel pump.

 

When my extra relay is added, power from the original headlight wiring that comes to the stock 521 headlight relay is used to only power the coil in my relay.   The original headlight fuse, wiring from the original fusebox, into the cab, and back out to the original headlight relay is only used for the added relay coil.  The contacts on this relay apply battery power directly from the source you choose, to the original relay, where power would have come from the headlight switch.

 

Go to post 33, in my thread, (  http://community.ratsun.net/topic/30606-my-ratsun-datsun-521/page-2  )and you can see the difference in the positive side voltage drops to the headlights.  The numbers are the difference in voltage from the positive battery post, to the terminal on the headlamp itself.   1.721 volts was used in the original wiring from the battery to the headlight.  After adding the second relay, and bypassing the original fusebox, cab wiring, and headlight switch, the voltage drop from the positive battery post was .464 volts.

[ggzilla]

Alright, that makes sense. So in this system, the power circuit bypasses the headlight switch, but otherwise the power side goes through the existing headlight relay, existing headlight wires and headlight sockets. But it does bypass the Fuse Box and the Headlight Switch.

 

I suspect he's got a problem in those parts, because it shouldn't blow fuses with 55w bulbs.

[DanielC]

Maybe this will help.

The red I drew is the power flow for headlight current.  Headlight current goes to the fuse box, but does not actually enter it, but goes directly to the blade fuse you see in the picture, and to pin 30 of the new relay.

 

The fuse in line with the extra orange wire is the stock headlight fuse.  Above that fuse in the picture is the red wire going to the headlight switch.   Switched headlight power returns to the original headlight relay on a red wire, with a yellow stripe.  That wire is pulled off the original Datsun headlight relay, and used to switch the new relay on, by going to pin 86 of the new relay.  Pin 85 is grounded.  In the new system, you turn the headlights on, the new relay closes.  The only current that goes to the stock headlight switch is the current to switch the new relay.

 

The original relay now had a open pin, this is pin 2 on Datsun wiring diagrams, for 521 trucks.  This pin is connected to pin 30 on the new relay. 

If the new wiring or relay has a problem, you can easily return the headlight system to stock by removing the short jumper from the new relay off the original Datsun headlight relay and then taking the red with yellow wire off the new relay, and plugging it back to pin 2 on the Datsun relay.

 

With my new system, headlight power bypasses the fuse box, the wire harness into the cab, the connectors to the cab harness by the glove box, the cab harness to the headlight switch, the switch, the headlight switch to the cab harness again, another connector in the cab to engine room harness, and that red with yellow wire finally ends at the headlight relay.

 

"I suspect he's got a problem in those parts, because it shouldn't blow fuses with 55w bulbs."

I believe on high beams, you have two 55 watt bulbs, and two 60 watt bulbs on.  Lets just call it four 55 watt bulbs to keep it simple.  That is 220 watts total.  Divide that by 12 volts, that is 18.333 amps.  Theoretically, the stock headlight fuse on a 521 is 20 amps, and the system should be OK. 

 

But the fusebox is 40 plus years old, and not really in a good location.  I can guarantee it has gotten wet sometime in it's life, and the connections in the fusebox have degraded some.   and thewre iare just the problems with the glass fuses Datsuns use.  The element in the fuse is just soldered to the end caps.  If there is any resistance in the fusebox connections under the fuses, or the clips to the fuse itself, 18 or 19 amps flowing through a fuse can easily create enough heat to unsolder the fuse element for the end caps.

 

 

Just foir reference here is a Datsun wiring diagram of just the lights.

 

This is what the bottom of a 521 fusebox looks like. 

Notice the connections on the bottom of the fusebox are just riveted.  On the left side of the fusebox, the second screw from the top, is the main power in wire coming from the battery.  In line with that screw is the red wire that goes to the headlight switch.  Notice Datsun tried to make the headlight power go through the fusebox with as few connections as they could, but you still have the headlight power coming in on a lug, riveted to one fuse clip, through the fuse, to the second fuse clip, to a rivet, to the out lug, and then to the spade connector and finally into the red wire.

 

 

[ggzilla]

Cleaning the Fuse Box may fix the problem without fitting a new relay and fuse.

 

1. Disconnect the battery

2. Remove all the wires from the fuse box (take a photo first, or write them down carefully which is which)

3. Take the fuse Box in the house and soak it. Fill a small bowl with distilled white vinegar from the grocery store. Soak for 10 minutes.

4. Rinse with water with a little Arm & Hammer mixed in to nuetralize the acid from the vinegar. Then rinse with plain water

5. Let dry thoroughly/overnight

6. Put a little dielectric grease (a LITTLE not a LOT) on each copper terminal (front and back of fuse box) to keep moisture corrosion minimal

[DanielC]

The steps you outline in cleaning a fuse box are a very good idea, and probably should be done to almost every 521 still running, but you still have a stock 521 fusebox, that was adequate for a stock 521, when it was new.   They are now over 40 years old.   Almost all 521 trucks have extra electrical accessories added to them or in the case of headlights, higher wattage headlights.

 

Every wire has resistance.  Every connection no matter how clean adds resistance.  Every time you connect and disconnect a switch, it creates a tiny spark, and that eventually wears out the switch contacts, and adds resistance.

There are two ways to reduce the resistance of a wire.  Shorten it, or use bigger wires.  The only way to eliminate connector resistance is to eliminate the connection.

 

Yes, you can clean the fuse box with vinegar, and neutralize that with baking soda.   And it will still corrode again.  If the clips have ever gotten hot, the heat has removed the temper of the metal in the clip, and it does not hold the fuse as tightly.  

 

On a 521, it is really easy to add this relay, I described.   It has two advantages.  In my case, it reduced the voltage drop in the positive side of the headlight circuit from 1.721 volts to .464 volts.  This happens because it removes about 5 to 8 feet of wire from the headlight circuit, and remove many connections. This makes the headlights brighter.

The second advantage, it removed the electrical load of the headlight current going through a 40 year old fusebox.  With stock headlights, it takes a 14 amp load out of the stock fusebox.

[jrock4224]

Alright here's where I'm at, running low beams I use two 55 w h4 blbs ... They work fine it's when I hit the high beams which triggers another set of 65 w 3k bulbs to come one which means I have a total 240 watts of lighting to be on few minutes later boom popped fuse..... Never had the issue with stack lighting and I plan to run a hid in my low beam....I would still like to use my high beams as my 3k high beams that all come on with my high beams but it blows the fuse.....

[jrock4224]

Check that my high beams are 100 watts each and low beams are 65 ea. so that's 330 watts....

[ggzilla]

Yes, 100w bulbs are a lot different than 50w bulbs ... it will blow fuses. Use a relay.

[banzai510(hainz)]

I just got a H4 harness and never had proplems. stock wiring is intact.  just use one outer pass side lamp to trigger the new harness.

Minimal thinking involed

[ggzilla]

Hainz, what do you mean by that?

[DanielC]

"boom popped fuse..... Never had the issue with stack lighting"

Stock Datsun 521 headlight wiring is designed for 2 37.5 watt lampe, and two 50 watt lamps.  That is 175 watts total.  175 watts draws about 14 .5 amps.  A 15 amp fuse should be fine, most 521 trucks have a 20 amp fuse for the headlights.

You have 330 watts of lights.  That is 27.5 amps, almost double the current the stock headlights draw.  In fact, that is getting close to the total output of the stock alternator.

 

Drawing 27 amps through a 15 or even a 20 amp will make it blow.  That is what it is designed to do.   The fuse is there to protect the wires. 

Before you ask, you cannot just put a bigger fuse in.  If you do that, the fuse will not blow, and the headlight wires will become the fuse, and they burn, and that destroys only the wiring harness if you are lucky, and it could cause a fire, and burn your truck.

 

Here is one headlight harness already made.  there are lots off options available,  use google.

http://www.speedwaymotors.com/Headlight-Relay-Harness-Kit,58825.html

[jrock4224]

Running a saturn alt ...... Never tried a larger then 25 amp fuse.....that was only cause I had to one night when I inadvertantly hit the high beams.....and didn't know it till it was pitch black....... I have a left over relay harness for hids with dual head lights like that but was wanting to retain the factory wiring if possible obviously knowing its brittle frail and prone to failure and a potential liability

[Laecaon]

Relay the headlights. Up it to at least 14 gauge wire.

[jrock4224]

So fine easy enough what do I do with the green wire off the stock relay

[DanielC]

Here is a diagram of the wires for the headlights of a 521.  I took a schematic, and erased most of all that was not headlight wiring, and left this.

The stock 521 headlight relay had four connections.  Power in, Low beam out, High beam out, and coil ground.  The coil is wired to power in inside the relay.   The relay sits with the power in switched to the low beam out, most of the time, even when the headlights are off. 

When the green wire is grounded, usually by the turn signal, the headlight relay switches to high beam.

 

My opinion, 14 gauge wire is too small for your application of 100 Watt lamps.  It would be OK for 55 watt lamps.   I will get disagreement on this, but if you are going to go to the trouble to use 100 watt lamps, you may as well use more than adequate wiring.

I would feed each 100 watt lamp, with 12 gauge wire.  If you join two wires together, each from a 100 watt lamp, go up to 10 gauge.  You can probably stay with 10 gauge wire for the wire carrying power from the relay to the four high beam lamps.  You also need to feed the relay power, from the battery with 10 gauge.

 

This is a auxiliary relay from Summit racing. 

This relay is handy because it has two 87 connections, instead of a 87, and a 87A.

 

On a 1974 Ford pickup I have, I upgraded the headlight wires.  I mounted two of the KC 3300 relays in a box, along with two fuses, one for each relay.

 

This is how I wired it for the Ford pickup.

 

I am using one relay for high beams, and one relay for low beams.  The relay coil for both relays is grounded.   The low beam relay gets power from one original headlight socket, green wire.  The high beam relay gets power from the red wire on the original headlight socket.   New heaver wires feed power to new headlight sockets.

 

[ggzilla]

If the length of + and - wire is 10 ft total, expect 12A draw voltage drop to be 0.6V at 12V with 14 gauge wire and 0.4v with 12 gauge wire.

 

With a properly done relay, there should be less than 10 ft of power cables.

[flatcat19]

All very interesting.

Good read.

[banzai510(hainz)]

H4 harness is already engineered out. correct wire sizerelays ect......

Just pay 25 to 40 bucks or more for a better one. From Where ever.

Plug and play.

 

MINIMAL thinking.

took about 15min to install on my beater 510

521 longer, as its a switchable power(as trigger) so I had to move or add a jumper in the supplied harness I got from 4 Crawlers a Toyota site.

also H4 plugs dont fit thru the back side of the Light housing on 521s so I had to de Pin and reinstall in front of car.

 

Fuse box wont know the difference. It only sees the trigger current.

The H4 harnesss hooks up to batter via the starter lug

[ggzilla]

Painless Wiring Headlight Harness with relays

[jrock4224]

frank

 

[jrock4224]

H4 harness is already engineered out. correct wire sizerelays ect......

Just pay 25 to 40 bucks or more for a better one. From Where ever.

Plug and play.

 

MINIMAL thinking.

took about 15min to install on my beater 510

521 longer, as its a switchable power(as trigger) so I had to move or add a jumper in the supplied harness I got from 4 Crawlers a Toyota site.

also H4 plugs dont fit thru the back side of the Light housing on 521s so I had to de Pin and reinstall in front of car.

 

Fuse box wont know the difference. It only sees the trigger current.

The H4 harnesss hooks up to batter via the starter lug

 

I need to know more abou thtis jumper harness...... got my stuff just need to understand this concept better... please advise ....