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521 headlight relay work around.


jammin

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Hello all.  My headlights went out on my 521, and all indication is that it is the relay.  I have gone over the boards and read about rewiring with a newer relay but for the life of me I cannot get anything to work.  I have done 2 different styles of wiring....directly to the new relay from the battery and then using the old relay for high/low, as well as just wiring straight to the new relay.  nothing seems to work.   One thing I have noticed is that the Red / Yellow combo wire that is the power from the light switch does not have juice when I pull the light switch out to the "lights on" position. Running lights work as well as interior gauges.  No high or low beams.  If I run power from battery to new relay, I can get lights, but they are constantly on unless I take the ground off the battery. The high / low wire doesn't see to do anything with the relay at all.

 

So..quick thought.  How bad would it be if I run power off of the wire going to my parking lights into the "control power" spot on my new relay? Wouldn't that give me at least low beams while my running lights are on?  Or should I just rewire a new switch for headlights?   Full day burned up in garage and little frustrated!

 

Or...if it is my switch, any swaps with old Datsun switches would work?

 

 

Many thanks in advance.

 

Ben

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OK... first the relay can only choose either high or low beams. It cannot choose none. The relay can only be on or off so either high OR low beams are the only choice. When the headlight switch is on some headlights MUST be on. (well unless all burned out)

 

The Red wire is power from the light switch. With the relay off, power flows through the relay harmlessly and out the Red/Black wire which goes to both low beams.

 

The Red/Yellow stripe wire goes to the dimmer switch on the steering column. When the dimmer switch is clicked to high beams it grounds the Red/Yellow wire. This draws current through the relay energizing it and closing the contacts that also send power to the Red/White stripe wire which goes to all four bulb high beams.

 

Low beams are on at all times the headlight switch is on. Switching to high beams just turns on extra bulbs.

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I hate to say this, but there are some minor errors in the above explanation.

Red wire from fuse box to headlight switch is headlight power, and depending on year, the park light power.  More on that later.

Red wire, with yellow stripe is switched power from headlight switch to headlight relay.

Red wire with black stripe is low beams,

Red wire with White stripe is high beams.

a small light green with a white stripe wire goes to the steering column.

There is a black wire at the headlight socket, it goes back to a lug that is under one of the bolts that hold the voltage regulator.

 

Lights only wire diagram.

LightWires.jpg

 

Mostly all the wires.

521wires.jpg

 

The headlight relay has four connections.  They are as follows.

Power in.

Low beams, normally closed connection.

High beams, normally open connection.

Coil ground.

 

The relay coil is wired inside the relay to the power in connection.

The coil ground wire goes to the steering column, where it is grounded, when the dimmer switch is in high beam position.

 

 

Now, the park lights.

Some 521 fuse boxes have three always hot fuses, and three ignition switched hot fuses.  If this is your case, the red headlight power wire also powers the park lamps.

Other 521 fuse boxes have four always hot fuses, and two ignition switched fuses.  these 521 trucks have a separate headlight and parking light fuse.

 

With the headlight switch on, you should have power on the red wire with yellow stripe at the headlight relay.

If you do not, check to see if you have a "three always hot", or a "Four always hot" fuse box.

 

If you have a three always hot fusebox, check the wiring between the light switch, and headlight relay.  Pay attention to the harness connectors behind the glove box, where the engine room harness connects to the cab harness.  Check also the plug on the light switch.

 

If you have a four always hot, in addition to the checks above with the three always hot, you could have a problem with the red wire from the fuse box to the light switch, INCLUDING the fuse.

 

Glass tube fuses can look good, and be bad.  The fuse element is just soldered to the end caps, and if the fuse gets hot, without blowing, the element can come unsoldered.  This is very common with fuses carrying headlight current.

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Daniel... there must be different diagrams for different years. I checked mine again.

 

Red wire at relay is power from the headlight switch.

 

The Red/Yellow stripe goes to the dimmer switch which grounds to turn high beams on. In your description above what color wire on the relay grounds the coil to turn the highs on?

 

The other two go to the headlamps and I agree.

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Mike, first, absolutely no disrespect from here. 

This is Ratsun's headlight relay.  From top to bottom.  Light green wire, red with (dirty) white wire, red with black wire, and red with yellow wire.

Unplugging the light green wire, headlights come on, low beam, and moving the dimmer switch does nothing.  You might notice the red with yellow wire goes off to another added relay.

HeadLiteRelay2_zps53953f2d.jpg

 

This is a better picture of the added relay.  Red with yellow stripe wire goes to the grounded coil of this relay.  This relay takes fused power directly from the battery, and sends it to the original headlight relay power in connection.

HeadliteRelay1_zps76a26582.jpg

 

Is there a possibility that Canadian 521 trucks have different from USA 521 trucks?

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Mike and DanielC  Is there 2 wiring harnesses for the 521 in respect to the 2 fuse boxes used in the trucks?

 

Datsun521FuseBoxBacks2Types.jpg

 

I call the 2 harnesses early model 521 and late model 521.  I had both wiring diagrams until I had a hard drive crash.  I will look at my old CD archive and see if I can locate both diagrams again and post them.

 

Daniel you might have them.  If I remember correctly one of the diagrams was from an old Mitchell Manual.

 

Please correct me if I am wrong.

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Well Ben, the first thing I would do is check to see if you have power to everything, turn the lights on and check both ends of the fuses, the ones that have power should have power at both ends of the fuse, now grab each wire that is plugged onto the spades on the fuse block and wiggle them while watching the headlights, if they start flashing or stay on once they make a connection, then the fuse block has issues, also grab onto the fuse itself and wiggle it.

My fuse block did the same thing, sometimes the headlights would be on, but the park lights would not work, sometimes the brake lights didn't work either

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Follow up as promised.   Big thanks for all the information, but Wayno get the prize for the Keep It Simple Stupid advice.  Sure enough...wiggled the fuses and the lights came on.  I never would have gone that route since I had replaced all of the fuses as well as cleaned the fuse block terminals not less than 6 months ago. For now, I got two inline fuses and have run the lights and the parking lights straight from battery kind of as was suggested from the gentlemen above. Seems like there is no adverse effects from not going through the fuse box and the inline connectors are more secure that the clips on the fuse box. I used some wet/dry sand paper and cleaned all contact points in the old relay as well as a nice coating of crc and resealed it, so hopefully it will keep working for another 40 years! 

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