Question about Toyota Corolla
If the unit is turning off when you turn the headlights on, check that you haven't used the illumination wire as ground.
The illumination wire will normally measure as 0V compared to chassis ground. When you turn the headlights on it will go to 12V compared to ground. With the headligts off, if you measure your constant power and switched power (aka 'Accessories') lines against the illumination wire you'll measure 12V and everything will seem alright. However, if you turn the headlights on and then measure again (now that the illumination wire has gone from 0V to 12V) you'll measure 0V, since the voltage difference between the 12V constant/switched power and the 12V illumination wire is zero - they are both now at the same voltage and no current will flow.
Once you find (or install) the correct ground wire and you should be right.
Posted on Dec 30, 2008
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