what is this diode for?!

Timmyt79 · Jul 13, 2016

Hi all. So trying to sort out the appalling wiring on my 110..removed dim dim,rear window heater relay (don't have one) and I have come across this diode amongst the mess and don't know what to do with it and we see if it's blown could it have some thing to do with some of the issues in been having.any help is much appreciated

Kwakerman · Jul 13, 2016

Timmyt79 said:
Hi all. So trying to sort out the appalling wiring on my 110..removed dim dim,rear window heater relay (don't have one) and I have come across this diode amongst the mess and don't know what to do with it and we see if it's blown could it have some thing to do with some of the issues in been having.any help is much appreciated
View attachment 103659

Possibly this one (check wiring colours at both ends of diode).

Timmyt79 · Jul 13, 2016

Thankyou for the reply..so its either for brake fluid warning,handbrake (cant say i have know that to work at all) or oil warning lamp? How can i test to see if its functioning before i check complete loom?can i just bypass it?
Not sure on wiring colours at mo as had enough of the bloody thing for today! :-(

Roaming Wombat · Jul 13, 2016

Use a multimeter to check continuity across the contacts on the diode in both directions, it should only beep in one direction. If it beeps in both directions the diode is blown.

Kwakerman · Jul 13, 2016

Roaming Wombat said:
Use a multimeter to check continuity across the contacts on the diode in both directions, it should only beep in one direction. If it beeps in both directions the diode is blown.

Or doesn't beep at all

Flossie · Jul 13, 2016

I'm simple terms, the arrow shows which way the current is meant to flow, you need continuity that direction but not the other.

Timmyt79 · Jul 14, 2016

Thank-you all for your help..will post results

Timmyt79 · Jul 14, 2016

Hi all...so back at the electrics again today...no continuity through the diode in either direction.no need...so guess it's goosed.what's best to replace it with?also one lead is black the other is black with a pink trace??,

Flossie · Jul 14, 2016

I know disco's have one in the back door , for the red round light. Same spec as well.

Timmyt79 · Jul 14, 2016

Sorry Flossie what do you mean by red round light? Could this little bugger have some thing to do with my rear fog light having constant live? ( which I'm struggling to trace :-( ) also my stop lights come on with my tail lights!but they work fine if no side lights are on :-/

Timmyt79 · Jul 14, 2016

OK so found another that is duff...this time brown with yellow trace....alternator warning?.
I'm beginning to thing that all my

troubles are down to this little beauty.
Anyone have any ideas what it is/for?have pulled loom from chassis as far as I dare and all seems OK...traced behind dash to dropbox and out into engine bay and all seems OK no damaged to red/yellow or blue/purple.....

Kwakerman · Jul 14, 2016

What sort of meter are you using, two diodes duff is a bit suspicious / rare

Timmyt79 · Jul 14, 2016

I'm using a multi meter...nothing special...just put it onto 'Wi-Fi' symbol..test for sound..then test diode,switch etc.I wouldn't put anything past the electrics in this thing to be honest :-( think I also have duff brake switch,reverse with and duff lock switch !! (The diff never has lit up)

Flossie · Jul 14, 2016

Timmyt79 said:
Sorry Flossie what do you mean by red round light? Could this little bugger have some thing to do with my rear fog light having constant live? ( which I'm struggling to trace :-( ) also my stop lights come on with my tail lights!but they work fine if no side lights are on :-/

It's been a while but a mate was scrapping a disco 200 and in the tailgate door there is a round red light on the shut face iirc,it lights up when the door is opened at night iirc.
I blagged it for my camper door but it didn't work correctly until I found the diode was needed. That was inside the bottom of the tailgate iirc.
If you have diodes then they are necessary for something.
My 1986 110 doesn't have any diodes so you must have an accessory that mine doesn't. Like handbrake warning, brake fluid warning or the like.

Flossie · Jul 14, 2016

Timmyt79 said:
Sorry Flossie what do you mean by red round light? Could this little bugger have some thing to do with my rear fog light having constant live? ( which I'm struggling to trace :-( ) also my stop lights come on with my tail lights!but they work fine if no side lights are on :-/

It's been a while but a mate was scrapping a disco 200 and in the tailgate door there is a round red light on the shut face iirc,it lights up when the door is opened at night iirc.
I blagged it for my camper door but it didn't work correctly until I found the diode was needed. That was inside the bottom of the tailgate iirc.
If you have diodes then they are necessary for something.
My 1986 110 doesn't have any diodes so you must have an accessory that mine doesn't. Like handbrake warning, brake fluid warning or the like.

Flossie · Jul 14, 2016

Oops! Sorry for the double post.

Timmyt79 · Jul 14, 2016

Flossie said:
Oops! Sorry for the double post.

Ah ok though it may be something like that!
One is def for oil warning and I suspect the other is handbrake as warning light has never worked on that!what to reply e them with though?just a 1.2 ohm resistor?currently in barn at moment trying to work my way through the horrid electrics now :-(

Roaming Wombat · Jul 14, 2016

You'll likely need to replace with new diodes, either some research on google as to what the spec needed is or take the duff unit into Maplin (or an independent electronics place).

Just replacing with a resistor will allow the current to flow in both directions so may give some unexpected behaviour.

brian47 · Jul 14, 2016

The two main characteristics when selecting a diode rectifier are maximum forward current and the maximum blocking DC voltage (sometimes called the peak inverse voltage PIV).
A reasonable diode rectifier for almost all 12 volt motor use, except in the alternator controller and ECU use is the 1N5401 available from Maplins and other sources for about 60p each.
These are 3 Amp devices, plenty of capacity for warning lights and a PIV of 100 volts DC.

Diode rectifier Physical drawing and matching circuit orientation.

Roaming Wombat · Jul 14, 2016

That's some fag packet engineering right there! Excellent description and doodle

what is this diode for?!

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