Door Lock Relay safety fuse install

By: PCH
January 8th, 2012
10:26 pm

Door Lock Relay safety fuse install

The Door Lock Control relay is very sensitive to the electrical overload and can fail if extra care is not taken when modifying the dome light with the aftermarket LED's or adding load to the dome light circuit. Here is one example of the damage that can be caused by that:



The transistor that controls the dome light overheated and that ruined the whole circuit board causing the complete loss of the electric door lock operation (this is the picture from one of the threads discussing this problem). The $400 part sure needs some extra protection even though the dome light has its own 15AMP Dome fuse.
The factory installed light bulb draws only 0.5 Amps and the relay is surely capable of handling some extra current, but by the time the Dome fuse blows the original load will be exceeded by the current about 30 times stronger. That is why we need to add another fuse to the wire from the relay to the dome light:



I bought the universal inline fuse holder and installed it in the Red/Yellow wire at the passenger side D pillar. The wires were extended to have the holder mounted in the easily accessible spot behind the tail light service cover:





The smallest fuse available to fit that holder is 2 Amps. Even though it is 4 times the current that the stock bulb draws, it will protect the relay better than the 15 Amp fuse we have. Now the ultra expensive relay is safer from the overload by the occasional short or added lighting modifications.
Now I will be installing my flood LED from Oznium with the peace of mind. It draws less current then the original bulb but with any modification the extra care is needed, especially when we play with the car's electrical system.



Here is the Interior light diagram for reference: http://scionlife.org/Scion_Docs/2004...s/IntLight.pdf

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27 comments on "Door Lock Relay safety fuse install"

  • SAKURA
    January 8, 2012 at 10:39 pm

    great info victor! i will be doing this saftey mod this week.

    btw, where is the Door Lock Relay located?

  • PCH
    January 8, 2012 at 11:21 pm

    It's inside the dash:





    The second pic was posted by j3st3r before somewhere so i'm linking it too.
    The Red/Yellow dome light wire can be spliced in few different locations, the d-pillar was the easiest for me since i had that trim removed earlier anyway. Some more info on that wire routing here: http://www.clubxb.com/forums/showthread.php?t=34567

  • RyanR
    January 11, 2012 at 8:10 pm

    Thanks for this write up!!!

    Coincidentally, I was also adding some interior lights over the past 3 days. So fortunately, I read this in the morning and was able to get a mini fuse holder this afternoon and had a chance to install it tonight.


    Now the $400 relay (that I didn't even know about ) will be safe from these:

  • PCH
    January 11, 2012 at 10:33 pm

    Good job! I see it's pretty easy to just unwrap the harness and splice the wire right behind access cover. The lights look great, how many amps fuse did you plug?

  • RyanR
    January 12, 2012 at 6:14 am

    Originally Posted by PCH
    Good job! I see it's pretty easy to just unwrap the harness and splice the wire right behind access cover. The lights look great, how many amps fuse did you plug?
    It wasn't too bad to do, but it is a very cramped operation, and the wire ends are at the minimum to work with. It would be much easier to remove the entire panel, but I was not motivated to do that.

    Thanks, definitely makes the car more friendly at night! I am using a 2A (mini) fuse like you suggested. I bought a combo pack so I have options up to 7.5A (I think) in case that one blows too quickly, if at all.

  • JOSEFF
    January 12, 2012 at 12:51 pm

    I just bought my safety fuse last night. Thanks!

    Oh and everytime I unlock my car my alarm goes off. Is this because I hooked up my led strips to my dome light?

  • PCH
    January 12, 2012 at 1:44 pm

    What kind of alarm? Don't you disarm it when you unlock?

  • JOSEFF
    January 12, 2012 at 1:56 pm

    Originally Posted by PCH
    What kind of alarm? Don't you disarm it when you unlock?
    It's the OEM alarm. And yes its supposed to disarm but instead my alarm goes off like I just pressed the panic button. It's really annoying.

  • PCH
    January 12, 2012 at 2:02 pm

    Do you mean OEM optional security? I don't know much about how it works, i've never seen a diagram for it- just installation instruction. What if you turn the dome light off? Will it still sound?

  • JOSEFF
    January 12, 2012 at 2:12 pm

    Just tried turning off the dome light and now my alarm doesn't go off. I guess that's what it was. I wonder why that happens though.



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