MR2 and Electrical Geniuses, please help.: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Sept. 20, 2010 8:18 a.m. pinchvalve SuperDork
The front marker lights on my MR2 went out, literally on the way to inspection. Doh! I am having a bear of a time diagnosing the issue.
1. The tail lights and rear side marker lights are on, so I know the basic circuit and switch are OK.
2. The front turn signals work, so I know that the ground and power to the front lights is OK
3. There are lots of lights sharing the same fuse and they are on, so it not that.
The only thing these 4 lights have in common is a ground, and that is OK because the signals work. The power comes from another circuit shared with the headlights, and they work.

So I think that there is a break in a line somewhere. Not really likely, I mean, how often to wires just self-destruct for no reason? I would love to trace out the lines, but the colors underneath the car do not jive with the diagram or the wires in the frunk, 6 inches away. Huh? WTF? Yes, the loom is OEM and unmolested.

I am thinking about splicing into the tail lights and running new wires forward. Any other suggestions?
Sept. 20, 2010 8:19 a.m. BoxheadTim Dork

Did you wave your multimeter at it to confirm that the light isn't getting power?
Sept. 20, 2010 8:37 a.m. PubBurgers Dork

On my wife's old MR2, the front markers and turn signals would work fine but the headlights were intermittent. It turned out to be the headlight switch. Replaced it and everything worked fine.
Sept. 20, 2010 9:54 a.m. iceracer Dork

First confirm if the sockets are getting current. There often are various connectors in a circuit. Just because the directionals work doesn't mean the parking lights will. Of course, always check the bulbs.
Sept. 20, 2010 10:34 a.m. racerdave600 HalfDork

What they said, always get a meter out and start at the sockets and work upstream. Also, make sure something didn't spike and blow the bulbs. Don't rule out the switch either.
Sept. 20, 2010 10:46 a.m. Taiden Reader

I have nothing to add, since all the good ideas have been covered already.
Sept. 20, 2010 1:40 p.m. Tyler H Dork

I think all of the exterior lighting is routed through that headlamp switch and it's known to be problematic.
Sept. 21, 2010 7:45 a.m. pinchvalve SuperDork

The trouble with tracing the wires is that a yellow and black wire leads out of the socket, goes into the loom, passes through the fender, and 6 inches later is gone. Did it change color? Did it just stop? Is it in the Bermuda Triangle? (Triangle? MR2? Get it?)

The switch seems a likely culprit. Perhaps there is one wire going from it forward and one back. I will check that next.
Sept. 21, 2010 12:23 p.m. racerdave600 HalfDork

That's why you need a wiring diagram. I would bet that one is available for download. I've found all kinds of strange wiring diagrams online.
Sept. 21, 2010 4:08 p.m. zipty842 Reader

The turn signal bulbs are dual filament. IIRC, power for the markers goes through those bulbs first before going to the side markers. Its not normal for toyota to randomly change colors in the harness, but they did change a lot of colors between 85 and 86 models. I no longer have any harness in my car to be able to look at where the splice is for the sides.