Electrical...Diode Location for Interior Light Circuit - Toyota Nation Forum : Toyota Car and Truck Forums

87_SR5 · 01-03-2005, 12:00 AM

At first, I thought my the drivers side door switch was bad and that is why opening the drivers side door would not turn the interior light on...but opening the passenger door will. I looked into it a little more and found out the wire going to the door switch isn't even hot like it is suppose to be. There is a diode between the drivers side door switch and the passenger side door switch and I think that is my problem. This is the only thing I can think of that is causing my problem...a bad diode.

Does anyone know where the diode location is for this circuit? The wire from the drivers side switch goes up into the wiring harness that travels up and across the dash, and then from there the wires for the interior light goes up the passenger side door jamb. So its either in the wiring under the dash (which is all wrapped up), or it is in the door jamb, or in the roof. It would be real nice if someone knew the location of it...save me a lot of head aches.

Its a 1987 Pickup SR5...no power windows, no power locks, no door courtesy lights...just the interior light.

Any help would be appreciated.

Thanks

GregoryM · 01-03-2005, 01:41 PM

Diode??? The door switch is on the ground side of the light circuit, thus, it is not "hot". If you find a diode in this circuit, you will be the first. Keep tracing that wire as it is not completing the circuit. Don't rule out the switch either. You have not tested it properly if you expected it to be powered.

reb · 01-03-2005, 01:57 PM

The schematic diagram for the '85 (which I would expect to be the same as for the '87) shows two diodes from the interior light. Since the light assembly has two connectors, with two wires each, I would guess that the diodes might be in the light assembly.

GregoryM · 01-03-2005, 02:54 PM

reb, help me understand. My older yota schematic doesn't have any diodes in that circuit. You say that there are 2 diodes "from the interior light." Which lines are they in? To the door switches, headlight switch, fuse box,??? Do the door switches make a ground or? I'm just trying to picture the circuit in my feeble mind. Thanks

reb · 01-03-2005, 04:51 PM

One goes to each door switch from the light assembly. There are a couple of other connections to the cathode side of the diodes. Those go to the door courtesy lights (one for each side). In addition, the LH side also connects to the seat belt warning relay and the "light remainder" (as spelled on the schematic). I suspect the "light remainder" is the circuit that sounds a signal when the headlights are on and the driver's door is open.

The door switches supply a ground to these circuits.

GregoryM · 01-03-2005, 05:59 PM

Thanks reb. My older SR5 doesn't have the "light reminder" and I discarded the seat belt warning long ago. I appreciate the reply.

87_SR5 · 01-03-2005, 08:47 PM

I don't know if I have the light reminder...I don't think I do. If I do, its not working. Here is a diagram:

The seatbelt warning relay doesn't work either, but I don't think that is causing my problem. The diode is there so the current will not pass back to the light from the seatbelt warning. So if the diode is bad, no power will be getting to the drivers side switch, with no power to this switch, it can't be grounded to turn on the interior light.

I knew this question was a long shot, but thought I would ask to see if anyone knew the location of the diode....anyone???

reb, I also have another diagram, but I only see one diode in the circuit like the one above....I will check the location that you suggested for the diode.

If anyone can shed some light on this...please do

Thanks

CraigW · 01-03-2005, 09:59 PM

If the wire colors match yours (Front RH=R/W Red/White / Front LH=R Red) You could take those connections loose & use a meter to see if the diode is o.k. and in that run. Most digital meters have a diode setting but an analog meter could be used also.

87_SR5 · 01-03-2005, 10:14 PM

CraigW...I will try that when I take the interior light apart...I have a multimeter that has a diode setting. I almost forgot I could try that...thanks for bringing it up. I still wouldn't know what the problem would be if the diode wasn't bad. I will get the light apart and see what I come up with.

Thanks for all the help

reb · 01-03-2005, 10:22 PM

87_SR5:

Your diagram is the essentially same as mine, minus the light reminder and the extra diode, which is not needed for an application that does not have door courtesy lights.

A thought--a broken wire could give you the same symptoms.

87_SR5 · 01-03-2005, 10:45 PM

Quote:

Originally Posted by reb

87_SR5:
A thought--a broken wire could give you the same symptoms.

That was my first thought, but after finding the wire and tracing its route...it goes up behind the fuse panel (drivers side kick panel), right from there it is wrapped into the wiring harness which travels all the way under the dash, which continues up the passenger side door jamb to the roof. A broken wire would do this, but the wiring harness it is wrapped in has been untouched and never taken apart for anything...its very possible, but I am just hoping the diode is the one causing the trouble. When I get the light apart I will definitly test the circuit and see what I get.

Thanks for the help

texas12 · 01-03-2005, 11:19 PM

Correct me if I wrong, it has happened once before!

If the door is open and the key is in the ignition, a buzzer will be going off. This comes from a little box tucked up under the dash on the drivers side. I did not like the buzzing so I disconnected the box. Well, that also made it so the interior light would not come on when the door was opened. I opened the little box and disabled the buzzer and plugged it back in. Interior light works again when door is opened.

I am pretty sure this only affected the drivers side and the passenger door would this trigger the interior light. It may have its own little box.

Do you know what I'm talking about? Does your buzzer work? Did you or a previous owner remove the box? I can get you an exact location, type of connector, wires attached, etc if you need.

87_SR5 · 01-04-2005, 12:53 AM

Quote:

Originally Posted by texas12

Correct me if I wrong, it has happened once before!

If the door is open and the key is in the ignition, a buzzer will be going off. This comes from a little box tucked up under the dash on the drivers side. I did not like the buzzing so I disconnected the box. Well, that also made it so the interior light would not come on when the door was opened. I opened the little box and disabled the buzzer and plugged it back in. Interior light works again when door is opened.

I am pretty sure this only affected the drivers side and the passenger door would this trigger the interior light. It may have its own little box.

Do you know what I'm talking about? Does your buzzer work? Did you or a previous owner remove the box? I can get you an exact location, type of connector, wires attached, etc if you need.

No, my buzzer doesn't work (I didn't know I had one). Maybe that is my problem. I will try to find the little box. Where is it located at? Would this have anything to do with the seat belt warning? Because I have that and it is doesn't work...and its part of the circuit for the light as the diagram shows. Let me know the location and I will see if I can find it.

Thanks

texas12 · 01-04-2005, 01:09 AM

Curiosity got to me. It is located at the top of the brake pedal arm. It is about 2" square with a 8 pin connector (only 7 wires). Labeled Buzzer with #'s 85991-89102 and 068900-0210. I believe the later is a nippon denso part number and the first being a Toyota #. I don't have access to my book and schematics right now, so I can give you any more details. However, I did unplug it and the passenger door did still trigger the light but not the driver door.