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Is it the relay?


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This is how the relay works in a Datsun 521 headlight circuit. When you turn on the headlights with the pull switch by the radio, power is applied to one contact of the relay, and the coil inside the relay. This wire is a fairly thick one, red with a yellow stripe. Power flows through the normally closed contacts of the relay, on a wire red with a black stripe, out to the low beam headlights, and to ground, after it goes throught the headlights. The wire coming from the relay has a "Y" connection near the left side headlight bucket. One leg of the "Y" goes to left side low beam headlight, the other leg of the "Y" goes to the right side low beam headlight.

When you move the turn signal switch forward, The light green with red stripe wire is grounded, and the relay switches from the normally closed contacts to the normally open contacts. Power is then removed from the red wire with black stripe, and applied to the wire that is red with a white stripe. This wire has a "Y" near the left headlight bucket, and another "Y" for both lamps on each side of the truck.

There are no connectors in the wires from the headlight relay, to the headlamps, other than at the relay, and the headlamp. If you have power at the relay contacts, and it is not making it to the headlight connector, the wiring is bad.

I would check the headlamps first. When the headlamps are known to be good, next check the headlamp socket plugs. They might be bad.

That should get you started on the headlight problem.

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OK. So lkfar I have found that BOTH low and high beam lights work. I was able to find the relay under the dash. It has a total of six spade connectors on it. Blue with red stripe is hot all the time( I fugure this is for the running lights), one Red with White stripe that goes to the low beams. This wire, before the relay, looses power when I switch to high beam.

The only reason I ask is because my 521, on high beam, would illuminate all four headlights. Is this the way the 620 lighting system works as well?



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You do know that the main beams have 2 filaments in them, right?


On a 620, and pretty much any quad-light car, when you switch from low beam to high beam, the main headlights will dim. They won't go out, just dim. That's because of the 2-filaments in the main beams (that's why they have 3 lugs instead of 2 like the high beams).


When you turn on the high beams, the main beams switch to the low-power filament. So they should dim. On NEWER cars (the 620 not included) the high/low beam switch had a passing mode, which would leave the low beams mains on and turn on the high beams too, making it ultra-bright, but the 620 doesn't have that mode.


So, if the main beams go OUT when you have the highs on, either the dim filament in the mains is burnt out, or you have a broken wire somewhere. The fact that only one light is affected means it is NOT the relay. It could also be a broken ground at that bulb- if the bulb is dim when the normal headlights are on (low beam) that'd be the problem for sure.

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Kinda sucks, I just got dispatched to go work in Bend. So now my poor truck will have nobody to play with for the rest of the week. Speeking of witch, I won't be checking here for a while.



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