[MENTION=441692]photoleif[/MENTION], where would these relays be located? I can hear them click once and then again as I turn the key to ACC, so would that be a faulty relay? Also about your speaker theory, how would I go about testing that?
[MENTION=99144]19963.4lsr5[/MENTION], without the bulb in place and the black lead grounded to the body I get about a tenth of a volt (pretty much nothing).
I'm no electrical master and this is all starting to get annoying daily driving with no lights and radio. Does anyone happen to have a wiring diagram for the radio to see if it'll turn on if I pull power from somewhere else (charging ports)?
with OEM-only parts, the main fusebox under the hood houses several relays. the fuse panel behind the lower finish panel (dash, behind the popout left and below the steering column) has several as well. in looking at the diagrams, i don't see that relays play much of a role, if any, with interior lighting and radio. those appear to be fused only.
with aftermarket parts however, it is possible that relays are involved, for instance my aftermarket key fob control module requires a relay, and an unnecessarily busy one at that. relays are designed to click. current running through a small coil inside induces a small magnetic field around an iron armature (a solenoid) which moves the armature to either the open or closed position depending on the relay's design. removing that current opens the circuit for the kind of relays i commonly encounter in automotive applications. you can hear the magnet on the armature click back and forth as it actuates. they are very simple devices designed to last a very long time. it is rare though not impossible for one to go bad.
when you switch the dome light switch onto the ON position (e.g., it would normally produce light if your circuit were working, regardless of door open or not) do you get the 0.8v reading across the terminals of the dome light, in addition to using the positive of that to body ground? if so, then that says proceed to next step. if it's actually 12v, well then problem solved there.
in terms of my horrendous guess (it's not even worthy of being called a hypothesis yet, let alone a theory) concerning wiring accidentally running through speakers, my train of thought was: aftermarket connectors (or installers) got goofed up, literally wires crossed, and someone was looking for a +12 constant or +12 switched, thought they had the right one by color or apparent gauge of wire, and hooked it up. i admit to some false starts of my own in this area, some years ago, which is why i bring it up. anyway, it is very unlikely but not impossible that the connector wiring is goofed up such that the dome light circuit got used as a switched source of +12, and the radio or its molex somehow bridges that to the speakers. again, this is admittedly very far-fetched since in an OEM world the radio circuit and interior light circuit are distinct. if there's some janky wiring, then all bets are off wrt which fuse controls what.
but i would take that dash panel off and look at every wiring connection to the radio. i believe in a prior post you said this is an aftermarket radio, not the OEM one, correct? download the installation manual for it, verify everything. i would also look behind the radio and verify that the OEM amplifier, which is a small box with cooling fins on the sides and a thick wrapped wire loom coming out the back, is not hooked up. an aftermarket radio doesn't need that amp unless someone's gone to some trouble to adapt it.
with that unplugged, and after you checked the connections to the radio, it's worth another try with the dome light prongs to check their voltage with the dome light switch set to ON. you ought to get +12 in general, and obviously something's giving you an open circuit, or one with a lot of resistance.
another test to be doing is to make very certain that the fuse for interior lights is good. visual inspection technically is enough most of the time, but set your new DVM to its continuity setting and touch each DVM lead to one prong on the fuse, held in your hand (polarity doesn't matter). it should beep or light or whatever your DVM is made to do with continuity. it's good practice to always briefly touch the DVM leads together in the continuity setting first (just by themselves) so you both know what it will do (e.g. light up) or sound like (beep), plus that you know it will test continuity at all. once you are certain that fuse is good (e.g. you got a beep), then put it back into the fuse panel and see if your dome light works.
