Can anyone recommend (or provide) a good "electrical engineering" overview of the DESIGN of the general cabin electrical system for 1999 (+/-) era Volvos (my girlfriend has a 1999 V70 XC I'm trying to diagnose). It doesn't have to be lengthy as long as it's practical and comprehensive enough to let me diagnose what is and isn't working. I'm not talking about the core of the main Engine Control System -- I'm talking about "the computers" (or logic chips or active components) if any, and circuits that turn courtesy lights on and off, detect whether doors are open, initiate the opening of the gas cap outer door, pop the tailgate door, etc., in response to flipping switches in the cabin area.

I'd like to be able to actually understand and diagnose whether suspect parts like a used cabin light assembly, a driver door latch, and signal/power cables to said parts are functioning or not (and how well). To do that, I need to know what kind of signals (voltage level, shape, and width, if any) the car is supposed to be sending back and forth to it's "Courtesy" system processors or analog circuits. Is it analog? Digital? Is it sending single pulses or encode pulse trains? .... Blind swapping of used parts from the junk yard by a friend with little to no electronics knowledge hasn't solved things and is starting to take it's toll on the cabin system (though he has the rest of the car working well). The problems are localized to a few features near the driver seat -- everything else works -- and the Engine runs fine. Which suggests the processors may be fine. The car was sitting a long time between owners (girlfriend recently purchased it), so it could be a couple corroded contacts, a new busted lead or two in connectors plugged and unplugged way too many times, etc., or something more serious. I have the door panel off (thanks for the videos) and no obvious damage to the wiring. Past time to take a more systematic approach, but that requires knowing how the components work electronically, and I'm not seeing anything on that.

Thanks for any help you may be able to provide.
Didn't see anything on this in my searches, but I'm new and may have just been searching in the wrong place.
And I've got a Ph.D. in physics, and past experience fixing advanced electronics (long ago), so just need a clue about how the 1999 era system works.

Robert

 

Volvo had very limited can bus network on a 99 - Throttle, engine, trans, abs and instrument cluster. Everything else is analog signals. Volvos wiring diagrams have individual systems/functions on each page - so you'll need those relevant pages for reference. Either find a pdf of 99 wiring (tp3938202) or post what specific things don't work and diagrams might appear. You mention door panel - a couple of pages related to gas, cargo door, locks, etc. is attached.