Dome Light Diode Fried (1 Viewer)

[supercarrera]

So my dome lights would not come on when I opened my driver door. I determined that the switch was okay so after some other circuit testing, I narrowed the problem down to where the diodes are in the circuit diagram.

I dug into the wiring behind the left front kick panel and quickly located the problem. As you can see, the diode completely fried!

Anyone experienced this before? So I guess I can just replace this with diodes that can handle about 1 amp at 12 volts and I'm good to go.

Scott

 

[Kernal]

Got a wider shot of that area?

 

[Timpanogos Slim]

You could use a couple 1n4001's but it might be better to vastly overshoot the current rating.

A couple 1n5408. Or get a large bridge rectifier and use the ~ legs as anodes and the + leg as the cathode, and clip the - leg because it won't be doing anything.

Radioshack 276-1185 for example, or whatever more-than-a-couple-amps bridge rectifier they have in stock or won't charge you shipping to get in.

I'd be concerned about what happened. Replace the fuse with a light bulb first, make sure there isn't a short to ground.

 

[blkprj80]

And just how many dome lamp lumens was that at anyway Skippy?

That much melted insulation would have me very worried. Any bad spots in the rest of the harness? Or does it just go to that box/connector there?

The crimps at the diode pair look good still, and rare for 3 to fail at once.

For the diode to get hot, you'd probably have to dissipate 10 or more watts. That would be 16A if Vf = .6V on the diode (big WAG).

Check your dome lamp before you power it back up. T-Slim's suggestion to use a light bulb is a great idea!

 

[Timpanogos Slim]

yeah the lightbulb replacing the fuse is the standard way to diagnose a short to ground.

If there's a short to ground the lightbulb lights. If not, it doesn't.

 

[landcrshr]

...Or get a large bridge rectifier and use the ~ legs as anodes and the + leg as the cathode, and clip the - leg because it won't be doing anything.

Great idea using a bridge rectifier, but it's the (-) leg you will use as the common anode. The two (~) legs will be the cathodes.

I too am concerned about what's going on there.

 

[Timpanogos Slim]

yeah, sorry, got it backwards.

Common anode schottky barrier rectifiers are a thing, i've held them in my hand, but somehow i didn't easily find any for some reason.

 

[george_tlc]

Just use 2 diodes, why make it more difficult than it needs to be

Seems to me that cooking the diodes likely means that +12V was shorted across the dome module such that +12V went to one side of the diodes and the other to ground - bad scenario. Bit sad that the dome fuse didn't blow rather than the wiring or did someone previously replace the fuse with a nail?

I would do some careful checking to see if was a simple dome light short versus something more serious...

cheers,
george.

 

[itbrokeagain]

Fwiw my amp was fried and that was tied into the dome circuit. Maybe worth looking into

 

[Timpanogos Slim]

Just use 2 diodes, why make it more difficult than it needs to be

the size and shape of the factory diode arrangement suggests that it can withstand many amps. Perhaps in excess of what the dome fuse withstands.

high-amp single diodes are harder to find than big bridge rectifiers. For people unlike us who don't have a bin full of random diodes already, and aren't already about to order some stuff from mouser, digikey, newark, etc.

 

[landcrshr]

^And the bridge rectifiers can be had with 1/4" spade terminals which will ease installation.

 

[supercarrera]

How about this one? It's a bridge rectifier I picked it up at the local electronics surplus house. It's rated at 25 amps and 400 volts.

By the way, by looking at the wiring diagram in the original post, I don't really see the need for the second diode. Is there one other than a convenient way to connect the two front door circuits?

Scott

 

[TrickyT]

Where is that wiring diagram from? My 1997 EWD (p/n EWD282U) shows the same components, but they are wired differently. The diodes let the Open Door Warning indicator light up if any door is open, but prevent the front doors from lighting up the rear dome light, and the rear doors from lighting up the front dome light. But maybe it's all different on your 1994.

 

[NLXTACY]

Soooooo was this using one of your LED lights?

 

[Timpanogos Slim]

That bridge should work fine

 

[landcrshr]

The diodes in the OP diagram isolate the driver's door from the other doors so that the key cylinder light only works with the driver's door.

 

[supercarrera]

Soooooo was this using one of your LED lights?

Yeah man they use hella powah to pump out that many lumens!

ahah I see what you're getting at but I didn't even consider that for a second. Thanks for pointing that out though NLXTACY!

I think I have a pretty good idea about what might have caused the diode to fry.

If you'll recall, I started a thread over the summer about when I had a little electrical fire. Well it turned out to be the wires inside my A-pillar. The problem stemmed from when I mounted a tweeter into the A-pillar using a screw. That screw went into the A-pillar and happened to cross both the sunroof and dome light wires. Surprisingly, nothing happened for a couple years until finally one day there was a lot of smoke! I'm pretty sure that's when the diode cooked.

 

[landcrshr]

Oh, and the diode isolation is also important for the door lock control circuit, although it's not shown on that page.

 

[HungryMedic]

Gonna revive this thread. My dome lights don't work nor do my door locks.

Some of these wires were taped together.

Any ideas?

1993 80

Edit, fixed it... Below

 

[bryson]

Gonna revive this thread. My dome lights don't work nor do my door locks.

View attachment 1020621View attachment 1020622

Some of these wires were taped together.

Any ideas?

1993 80

The crimp splices on the blue/yel wire are just the factory splices - tape them back up well and leave them alone. Your issue won't be diode related, but more likely a blown fuse or power supply issue. Possibly an issue with the port installed keyless/alarm system. Have you checked the fuses?