Need diode recommendation.

[chuzie]

I'm wiring a lighted rear view mirror in my '77.

It has two circuits feeding it. One from the ignition and the other from the dome. They need to be tied together so I want to use a couple diodes to prevent this backfeeding. The set of diodes I picked up fried rather easily and back fed into the dome light system which has about 8 lights attached.

Can someone tell me what specific diode I can pick up from radio shack that will work for this application. I really don't care too much about a little voltage drop since all it is powering are the two small bulbs in the mirror.

Thx,
Mike

 

[Viperwolf1]

How about a diagram of what you're trying to do? I don't understand the ignition switch part of this. How do you want to control the lights and what all lights are on the circuit?

 

[jgattonii]

Ive wired a lot of diodes in Alarm, Remote Start & Keyless entry systems & never had one fry. I believe what you need is a 1 amp blocking diode, referred to as a "1N4001/L."

This may be a dumb question, but is your dome light circuit positively- or negatively triggered?

 

[1975stroppebaja]

I believe what you need is a 1 amp blocking diode, referred to as a "1N4001/L."

x2 on that.

 

[chuzie]

There are two functions. One to have both lights come on via a trigger and the other to have each come on individually via a switch on the mirror. I wired the individual function to the ignition so I would not drain the battery if I accidentally left them on. The both on function is wired to the dome light switch on the panel.

I know the diode can blow due to an over load on the cathode side but can it overload due to the demand on the anode side? In other words, is it trying too hard to prevent the back feeding? With this is mind, a 1N4001/L is still a good choice? Is a 6A 50v rectifier diode overkill?

 

[Viperwolf1]

A single 1 amp diode in the org wire should be plenty. You don't need one in the pink wire.

 

[Steve83]

I don't get why you think you need any diode. The lights are probably already designed to work with the 2 separate circuits, so leave them separate. What was the donor vehicle for this mirror? Are the switches on the face or the bottom? How many wires? Does it look like these?

 

[chuzie]

It has two front switches and 4 wires from a mid 90s chevy s-series. Without diodes, when I hit the dome it backfeeds to the ignition and powers my accessories and when i hit the ignition it backfeeds to the dome and turns on all my lights.

 

[jgattonii]

Backfeeding may be happening through relay. Post another drawing of all the wires and what they need as opposed to how you have it wired.

 

[surfer-b]

Try this, do away with the relay, take the pink wire put a diode on it, tie the Red and Blue wires to this, I'm just guessing the colors for the "Individual On" function. Now for the "Both On" function put a diode on the WHT wire and splice the ORG wire to the WHT. This should take care of the prob.

 

[chuzie]

This is all from scratch. I have nothing to reference.

To have both functions of the lights, the ORANGE and PINK wires both must be powered. When the white wire is grounded and there is power supplied, both map lights come on like a dome function. Where there is power and the white wire is not grounded the option to use the front face switched is enabled. The white wire is what used to go to the negative door switch.

It cant be backfeeding through the relay if the only power going to the relay is the switch circuit.

 

[Broncobowsher]

Radio shack, switching diode 3A rating, 50PIV (PIV=Peak Inverse Voltage). Having a PIV or amp rating higher then actual use is good. The highest PIV you should ever see in a 12V electrical lighting system better be under 20V, so a 50V rating is good save overkill.
They even come in a 2-pack

 

[chuzie]

Thanks Broncobowsher. That is exactly what I am looking for. I will let you know how it goes.

I can't seem to find it on the radio shack site. Do you think you can track it down?

The closest I see is the 1n5402 which is 3A, 200PIV

 

[jgattonii]

Just in case you are interested:
http://www.thirdgen.org/techboard/electronics/11747-newer-rearview-mirror-wiring.html

 

[Steve83]

...when I hit the dome it backfeeds to the ignition and powers my accessories and when i hit the ignition it backfeeds to the dome and turns on all my lights.

Sounds like you have it wired wrong.

Post another drawing of all the wires and what they need as opposed to how you have it wired.

x2

Do you have a wiring diagram of how it was connected in the S10? Some have 4 black wires, which makes miswiring VERY easy. You need the connector face pinout.

 

[chuzie]

I have no wiring reference for the donor vehicle. i clipped it and ran. I am going to install these diodes tomorrow and see what happens. The reason it is all jacked up is because I am trying to make the door open function work without door switches. Otherwise this would be an easy setup with no diodes. I would just send power to the ORG + PINK wires from the dome and ground both the white and black. This will power both lights with the dome switch and render the individual mirror switches inop.

 

[Steve83]

OK But it's pretty easy to add a door switch. Probably a lot cheaper & less work than fighting these diodes.

.

Another option easier than diodes would be to pop the mirror open & just hardwire the switches & lights how you want, so it works the way you need. You can delete that PC board inside it.

 

[chuzie]

Gotta have doors to have door switches. I have none. Plus, I want to use the dome switch function instead of the doors. Thanks for the idea though.

 

[surfer-b]

I was looking at your diagram where the ORG and PNK wires spliced together after the diodes, were they that way from the factory or did you do that when you installed the diodes? Also I have a 4 wire mirror that I got from a late 80's early 90's S-10, the way I described it early is how it was hooked up from the factory and it works the way you are wanting it to, however they prob changed somthing after those yrs.

 

[chuzie]

I was looking at your diagram where the ORG and PNK wires spliced together after the diodes, were they that way from the factory or did you do that when you installed the diodes? Also I have a 4 wire mirror that I got from a late 80's early 90's S-10, the way I described it early is how it was hooked up from the factory and it works the way you are wanting it to, however they prob changed somthing after those yrs.

I tried to duplicate what you suggested and it did not work. I am guessing they did something different with the wiring. The problem is that the factory uses door switches where I am not so I have to compensate and create a mechanism to control when to engage the ground wire (relay). Also, Chevy allowed the lights to stay on regardless of the ignition so my implementing a measure to prevent battery drain is also complicating the situation thus the need for the diodes.