Parasitic electrical drain?


Lexus LS400

I have narrowed it down to the DOME fuse in the engine fuse-box, but this fuse allows power to several things, steering adjustment, interior lights, trunk light and release, sunroof and central locking.

When I remove this fuse the drain stops.

But the problem is what thing?

So, does the wiring separate in a sub-box. I know it has nothing to do with the foot-well fuse-box, so is there a sub-connection that separates all these things. If there is, is it plausible to get at it easily or is it a case of removing bulbs, panels etc in all the things I have listed.



If you remove the fuse and connect a light bulb accross the fuse slots it will be bright when there is a load on the circuit. Turn off everything and see if the bulb dims to nearly dark indicating there is no drain. If it remains bright begine removing things from the circuit. Your first tries might be the trunk light and the vanity lights. Those have a history of turning themselves on mysteriously.


Um yeah?

I have already isolated the fault to the said Dome fuse with a multimeter, it powers several things, all those things automatically turn off, I need to isolate the fault further.

Can you please address the actual details of the question.

Thanks Zappy


“Central Locking” is the prime suspect…Steering adjustment?? Now we are in the twilight zone…But that’s #2


What I mean by steering adjustment, is that on a Lexus, when you put the key in, the steering wheel moves towards you and back away from you when you take the kay out. You can set it to where you want it to be and it retracts when you leave the car.

It is also on the dome fuse line.

I know what things it might be, because I listed them all, my queston is about testing for those items.

Can I get to a sub wiring box, or is that going to be behind the dash and too difficult to access, or am I just going to have to remove the lighting fixures, door panels and test stuff that way?


Try to find a connector that ties the power to each of those areas and seperate the connector. Then see if the current drops when the leads are seperated. If the current does go lower then you have found the circuit leg the trouble is on. You may need to get a factory manual for the wiring to show you where to locate the connectors.


Yeah, that’s what my original details asked, there must be a connector that separates all those things, but it maybe impossible to get to, this would be the simpler option in testing just to remove each wire, but not if it’s totally impossible to get to.

So I am asking if anyone knows where it is, if it’s possible to access, if not then should I just start taking out the fittings instead.



To get the detailed wiring information you want and need you are going to have to refer to a factory service manual. They cost more than regular manuals but provide much better detail on things like the wiring systems. It is well worth the investment in my opinion.

I would guess the best suspect for the trouble would be the steering adjustment system that is causing the trouble from the list of areas things you mentioned and are tied to the fuse. There may be other things tied to the dome fuse also. If you think the trunk light is a problem just remove the bulb and see if the current drops. Normal current draw while the car is parked should be around 25-35 milliamps for most cars.


You need a FACTORY wiring diagram for your car. It will show the approximate location of all the connectors and the wire color codes. Follow that “Dome” fuse to a junction box where they all tie in…