Wednesday 16 January 2013

Wiring the Subaru aux lights, part 10: updates and fixes

Okay, so the lights are wired up and working great, right? Well, not quite. There are a few strange behaviours that need addressing, related to using the stock switched ground of the Subaru high beam system for my own grounds.






Two of the updates are visible above - I tinted the foglights yellow and swapped the middle light for one that matched the other two. The other updates are to rectify some wiring mistakes:

  1. when the headlight switch is in the off position, the fogs and spots will be on if their switches are on (this is not supposed to be possible)

  2. if the new high beam switch is on while the car is off, the relay makes a strange buzzing noise under the dash
Essentially, if the headlight switch remains in the “on” position then the lights operate as they are supposed to (with the exception of the indicator bulbs). It seems that when it is in the “off” position, the high beam switch somehow is getting a ground connection and is activating the relays.

This is the result of trying to use a the high beam stalk switch wires under the dash rather than a wire closer to the actual headlights. I thought I could save myself running another long wire into the cabin, but the behaviour of the stalk switch wires is not what I thought it would be - the wires are sometimes grounded while other times they have a positive connection, and I could never quite fully pin down their behaviour.

Here’s the fix, and a prettier wiring diagram to boot (made using circuitlab.com). Click the picture for a direct link if it is not displaying properly:



Here are the changes:

1. No more wires to the stock high beam switch on the stalk. The + and - for the relays now come directly from the headlight connector high beam and ground wires.



(disregard wire colours above. Pin locations are valid for Subaru headlight connectors - other manufacturers may vary)

This required rerouting the positive wire for the relays and running one additional wire into the cabin for the negative. Note the headlight wires were not CUT, merely tapped into - which brings up the next point…

2. High beams can no longer be off when aux lights are on. Unless I wanted to add in two more relays and a few more wires to the other side headlight, this setup can no longer turn off the high beams when the high beam stalk switch is activated. I found I never really used that functionality anyway… I do have one less switch in the cabin as a result.

Everything now works as it was designed, and I think I can close the book on the saga of headlight wiring for now.

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