Thread: Spotlight wiring

Gary

Much more detailed reply than I was going to give, well done

Bottom line is it's much safer to use diode protected.

Resistor protected relays are available as well, but they suppress the spike rather more slowly than a diode does.

So a 40AMP diode protected relay is what you want

Steve

I sort of grasp the need for diode protected relays in the main fusebox with circuits controlled by the BECM but I dont see why running a simple set of spotlights on a separate live feed, directly from the battery, switched via a possitive feed (main beam) coming from another existing diode protected relay will be an issue.
Can someone explain. Where is any potential spike going?
Also some relays have a LED, light emitting diode to show they are on. Are these the same as diode protected relays.

Hi Wayne,

I guess it's like the old joke about why the Irish wear two condoms "to be sure, to be sure"

You are probably correct that a diode protected relay is not really required here, but given the cost and hassle associated with damage to any of the electronics on the P38, it's cheap insurance IMHO.

I would suspect the LED only acts as an indicator not as protection, though LED does stand for Light Emitting Diode

Steve

I imagine they would be different as an led needs a resister to limit the current. .... and if I remember right the annode and cathodle are reversed in an led?

The lights on the p38s are driven straight from the becm, most likely from an internal relay, but they are field sensed, which is why the becm knows if the bulb is blown.

You can just buy the doide and solder it in line.

The voltage spike comes from the low amperage side of the circuit ie the switching control. It is the energy remaining in the coil that creates the electro magnetic switch that is the problem.

Gary

Hi,

Gary is correct, if you look at the diagrams around, the diode is across the coil.

If you really want information overload, you can read this

http://www.autoshop101.com/forms/hweb2.pdf

Regards
Steve

I did not realize how complex it was going to be just to hook up a couple of driving lights. Is the spare relay (No.10) in the engine fuse box able to be used for the driving lights or does it make it more complex? Is this relay a diode protected relay? or does it need to be?
Back to the switch, which wire/s do you need to power up to make the switch turn on.
In the wiring diagram that Steve has shown previously in this thread by switching the power on by earthing the relay through the switch, will this protect the BECM from spikes when the switch is turned off if a diode relay is used?
I have certainly learnt that you just about need to be a professor to understand the electrical system of the P38 or you need information overload to try and comprehend.
Regards
Kev

To be honest, the diode is a pretty standard thing to do in just about any relay circuit and it's not p38 specific.

Yes the diode will protect the spike in his diagram. I've got some idea about electrical/electronics but I'm sure someone else will confirm.