SC300/400 Map light assembly electrical circuit repair
 

I'm about to embark on removing and dismantling my 1993 SC300's overhead map light assembly for inspection and electrical repair. My door light (cylindrical bulb) works but both my right and left map lights (small 8-10W round Toshiba bulbs) no longer respond. I've tried new bulbs and that isn't the issue. The right one shorted out some years ago but with the left one no longer working it's time to repair both of the circuits for them.

I'm just wondering if anyone else has had this happen with their SC map light assemblies. I cannot imagine they are that electrically complex internally.

I've never had that happen, but if you figure out which wires are the +12V and ground inputs, and confirm that the problem is in the light assembly rather than the wiring prior to it, I have a couple spares.

With the dome/door light still working, I would guess the wiring is fine. I assume the map and dome lights share the same constant +12V input, since the dome light can be turned on with the door closed (as opposed to some vehicles where it can only be triggered by an open door).

^^ That is what I plan to do, yes. I assume it must be local something inside the assembly itself because of the working main dome light and the vanity mirror lights. I plan to get into it shortly. A roadblock just came up in the form of a snapped LH window regulator so that must be dealt with first.

I have taken the map light assembly out once before to inspect it externally. There isn't really much to it, I think?

Craig - going through the diagrams takes away all the guessing game and saves time. The problem and solution will be right there in front of you !

Check Diagram #8 which I have sent you couple of months back about your car. Those interior lights have very simple diagrams , if pcb connectors are not burnt which is unlikely for both Left & Right , you just have corroded bulb terminals.

call me ;)

Thank you Gerry! I'm returning to this, finally, to get a handle on it and repair my issue. For the moment I'm going to repost here the image from that page on your thread which shows the electrical diagram for the map light circuit PCB.

Next, to test the terminals with my voltmeter and then pull the assembly out and clean/inspect it for the likely corroded terminals or hopefully not burned out PCB traces which would need new wire soldered in.

https://cimg1.ibsrv.net/gimg/www.clu...e68e73b1fb.jpg

Well, I fixed my issue but I feel downright silly about it now. I had no burned out connections and no corroded terminals. Everything was extremely clean in there.

I simply did not realize that the spring loading effect of the flat negative terminals had lessened over time and thus caused both bulbs to be sitting in their spots loose without making full contact to Ground. When I went to remove the bulbs to test the map light assembly I noticed they just wiggled in place. I had a good laughed out loud at myself and just pushed the Ground contacts in again to provide more positive tension on the bulbs.

Once I reinstalled both bulbs I pressed each map light button and--- they both came right on. I feel so silly now, not having checked the most obvious thing! ;D

At the very least, the electrical diagram Gerry has provided in this thread can help anyone who ever does happen to have a more complicated electrical issue with their map light assembly, although as was mentioned a few posts back it is so simple there is hardly anything to ever fail.

Anyway, I'm happy to have my map lights working again. I just wish I had checked the obvious suspects much sooner, haha!

Kinda crazy that both loosened up that much. If it were just one, it would be more reasonable to suspect something like that.

Well actually my passenger side loosened up many years back and I just assumed it was an electrical short that I needed to take care of... at some point. I was always busy with something more pressing so I put it off for years until the driver's side map light also stopped working. At that point I couldn't ignore it any longer and I felt very silly after realizing it amounted to nothing more than the Ground springs getting a slightly loose by a couple of millimeters. I could have addressed the issue with the passenger side a long while back in ten seconds.

If there *had* been a problem with the printed circuit board for the overhead map and door lights I could have fixed this by cleaning or repairing traces but there was no such issue and apparently no one has mentioned their having such an issue with the internal board.

Moral of the story: if your map lights stop working the #1 suspect is loosened Ground contact springs that keep the bulbs in there tight ;) Just pull the plastic lens out, remove the bulbs, push the springs inward a bit, reinstall the bulbs and your problem should be solved.

Ah, that makes sense. Unless you have a passenger regularly, there's no reason to care about that map light.

^^ Exactly. That's why it was convenient for me to keep putting off diagnosing what was wrong for such a long time. I always had working door light function and my driver's side map light always worked. It wasn't a pressing issue until it was.