hey guys,

having headlight problems with my 120y.. one headlight works on low beam and the other works on high beam but both won't work at the same time.. i have checked fuses and changed globes but the problem remains the same.. please help as i will spin a spanner but circuits are foreign to me.



mike

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The 120y is a gateway Datsun.

I had a quick look at a 120y wiring diagram and it looks like the headlight switch and wiring is all common to left and right sides. That is, one high beam fuse, one high beam switch contact and wire to the headlights does all the high beam. There's no relays or separate left/right fuses.
Therefore, if one headlight worked for low beam or high beam, then both should. Only a break in the wires between the left and right side should affect it.
High beam wire is red with white stripe, low beam wire is red with a black stripe, headlights grounded by a black wire.
Trace the wires and maybe test with a multi meter or test light.
Try brand new head lights off all else fails.

To check the earthing, disconnect any earth wires to the chassis and clean them up - you can scrape away paint to bare metal where the wiring has to contact the chassis, even use a star washer - then reattach. The battery negative must have a good connection to chassis and engine block, the alternator casing must also have a good connection to both. It's always good to fix up any earth points, this will save you being stopped somewhere in the rain with crazy electrical problems, or the cops complaining about your tail lights blinking like a Christmas tree.