1992 volvo 740 wagon ... today i was cleaning it with all the doors open and tailgate open also so i turned dome lite off.
when i was done i turned it back on ... ON meaning when the door is open it will come on.
but .. now when either left side door is opened ... NO lite ... open any right side door and the lite comes ON ..
has me puzzled ...
anyone know where to start checking ? ..
i don't really understand this dome lite switching system ..
there are three switches .. one sliding switch in the middle that moves front to back with three stops ... front , center , rear.
there are two 'throw' type switches on either side of this also with three stops ... right, center, left.
thanks for any help to this thread.
philip

 

the side switches are for the reading lights on each side, while the center switch is for the center main dome light.

any switch in the 'back' position means its on when the door is opened. in the front position is always on, and in the middle position is always off.

the drivers door is wired special so it triggers a timer circuit thats in the dome light circuit board, to leave the light on. the other doors don't do this, they should just turn it on/off when you open/close the door.

open the left rear door, but no other... does the red courtesy light in the door jam come on ? if not, then I suspect the door switch is bad. you might poke at the door jam switch a few times (fully depress/release it repeatedly) and see if it is intermittent or what. there's a screw next to the switch, this provides its ground, you might verify this screw is snug.



open the drivers door, ditto, does the red courtesy light come on ? (all 4 doors come on together, no matter which one you open).

 

i checked this morning ... the dome lite and the door 'red' lites come on when the doors are opened on the right side only.
on the left side 'drivers side' nothing.
checked bulbs .. all good.
this is odd because before i turned all the dome switches to OFF they all worked just fine ...
are the right and left sides on a different circut and fuse ??

philip

 

digging up the 92 schematic now...

its all on fuse 5.

the door frame switches go to ground. each switch has two contacts, one contact for the dome lights, the other for the door light in that door.

unscrew the little screw that holds the switch to the door frame, you should be able to pull the switch out a little so you can get to the wires behind it. ground both those wires, the appropriate lights should come on.

the left FRONT switch is wired a little different than the others... its wired to dome light pin 2, while everyone else is wired to pin 3. pin 2 is the delayed light timer

 

wow .. can't believe how helpful and fast you are man.
thank you so much.
going out to do these checks now ...
let ya know whats happeining --
i have ordered the original owner manual and workshop manual for my volvo from ebay .. not here yet.

philip

 

volvos factory service documentation was a whole set of greenbooks, probably a dozen or so to cover a single car. they are no longer in print one greenbook is electrical diagrams (and that book is model year specific), another on LH2.4 EFI, others on EZK ignition, suspension, steering, transmissions, etc etc.

 

yes i know ... i have to settle for a chilton repair manual

appearently there is no power getting to the left side doors.
after doing the checks you mentioned ... grounding the two wires .. nothing.
mulitimeter told me this also .. so the left and right side are seprate circuts ?
very odd.

I did find the original '92 740 wagon manual tho .. $24 .. NICE !

 

the switch is only a ground circuit. the light in the DOOR gets its power through the door wiring, of course, but the dome light gets its power directly... ALL of these are powered from fuse 5.

imho, the chilton books are awful and useless. 90% of them are generic boilerplate, mixed in with 3rd hand vehicle specific tidbits that may or may not be accurate.

in each door, the green-red wire is power to the door frame red safety light. green-red to pin 5 of the dome light is also power, and all of these are tied to fuse 5.

in each door switch, the brown-black wire is the one to the dome light pin 3 (all 4 doors tied in parallel so any door can ground this circuit)... the driver door also has a white-black wire to the dome light pin 2 for the aforementioned timer.

sorry I can't snag a copy of this schematic, darn things are copy protected something fierce, the viewing software even disables printscreen.

 

thank again ... i wont order that chilten book .. was about to ...

i am going out now , while the sun is still up , with my meter and do some serious checkin' ... got to be something simple like a corroded contact ..
i am the second owner .. original owner did nothing but maintain it .. great condition ..
worked and now don't work .. hmmm
thank you for all your very fast responses and knowledge bro.
be back tomorrow.
philip

 

well nothing new .. tired with messing with it for now .. wait untill i get a manual.
thank you for all your help pierce ..
philip

 

Hello Pierce,
I was wondering if you might be able to offer an explanation for the following: my dome light works when switched forward (on command) but won't work when switched aft (on door open). All other lights work on door open (map, safety and liftgate).
thanks,
Andrew

 

Sounds like the switch in the door is bad.

 

Each door triggers the map lights. Upon reading again I saw Pierce's note about the black and white wire for the dome light timer. Is that the purpose of the small circuit board in the dome light?
Does anyone know how to troubleshoot that?
I know it's just the dome light, but I like things to work.
Thanks

 

Master pierce! If only you could have posted that schematic. Now I’m going to have to ask you a slew of annoying questions as per usual… because I need my dome light to work… to be precise, I need the light to go OFF when all doors are closed with dome light switch in position 3 (all the way towards back windshield)…

First: About those door switches. On my 1990 740 GL, driver’s door-jamb switch has a brown/black (from dome light pin 3?) and white/black wire attached. All others have brown/black and black wires. I understand that green/red wires deliver power to each red door warning lamp and to the dome light. I have removed my driver’s inside door panel (I was chasing down a speaker problem when I stumbled onto this lighting problem I’m now fixated on) and can therefore see that the return wire from the red warning lamp in the driver’s door is white/black. Is the same true for every door? If every door switch’s brown/black wire is grounding the dome light, are the black wires (or in the case of the driver’s door only, the white/black wire) grounding that door’s warning lamp? But the wiring diagram I have attached (if I’m reading it correctly) shows every door warning lamp grounded by door switch via a white/black wire (UPDATE: That is in fact just what I found when I removed the left rear door interior paneling, namely a black/white wire returning power from the door warning power lamp, so I guess somewhere in the body of the car it becomes black)?…







Speaking of door switches grounding current flow… it seems that maybe mine aren’t? For when I was unscrewing them to check the colors of the wires attached, it seemed that when detached from door they continued to function as though they were still attached to door? But I thought the screw was what grounded the switch? Weirder was that even the door switch that completely failed its continuity test seemed to function. Does this mean that there’s a ground somewhere where there shouldn’t be? Is that why my dome light stays on even with all doors closed?

Nerding out now on the dome light itself, what is the function of the brown and black wires? Do they have any relation to the brown/black wires at the door switches? For that matter, is there any relation between the white/black wire in the dome light and the white/black wires in the doors? Could you begin with identifying pins 1 through 4 here? I think I have identified pin 5; is the black wire connected to pin 2 and the brown wire to pin 3? Does the black/brown wire of the drivers door switch connect to pin 2 and every other black/brown door switch wire connect to pin 3?



Thanks for your time and your patience.