Written by , edited by Greg

Only attempt this if you know what you are doing. This mod is performed entirely at your own risk. I am not responsible for any problems arising from your workmanship, your failure to follow directions, or your inexperience or unfamiliarity with electronics.

Dec 17/02

Thanks to my dying alternator, I discovered how to disable my daytime running light (DRL) system on my 1990 4Runner. When a Toyota alternator fails, it lights up three lamps on the dash (automatic transmission, or two lamps if manual transmission) and if you look through the schematics you will see that they are utilising diodes fed by the alternator charge circuit.

When my alternator failed, I found that my DRLs also went out... this was a clue as to how they have lights that only worked with the engine running. I had thought they used an RPM signal, but it turned out to be much simpler. Toyota uses the charge circuit to feed the intergration relay which controls the headlamps, etc. I replaced the brushes on my alternator (which was very easy since they bolt onto the back of the alternator), and began hunting for the intergration relay and this circuit. Sure enough, the schematics show a yellow wire with a red stripe, fed from the alternator to the relay (which is really a module), and when I tested the circuit it was only hot when the engine was running ("key on" shows ground).

I cut the wire and my DRLs shut off. I plan to wire a switch to this circuit so I can have DRL when I want, and be able to overide it when I want. Why do I want this? So when I have my fog lamps on I can turn the head lamps off and just use the fogs and park lamps. I also like the idea of warming up my vehicle with the lights off to keep my neighbours happy. I just find there are times when you want to turn off your lights, and thats the way I am.

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