unidentified electronic object

[Mephistopheles]

In my E Type there was an old alarm system from the nineties, which I removed. Unfortunately I had to find out the following: the wiring harness is a pure tinkering orgy. At the moment I‘m busy to get rid of the mess and restore the wiring harness to its original condition. At the contact switch of the handbrake I found an electronic component, which is neither original, nor does it reveal its function to me. Can someone help me and tell me what it is and why it is built into the wiring harness?
Thanks and regards
Holger

[abowie]

It's a zener werbler. It rectifies the passant signal to the flarad on the warning light.

[johnetype]

It's a diode. The green wire is the "door switch" trigger line for the alarm.

Alarms/immobilisers have a door switch trigger line which can be wired up to multiple door, bonnet, boot, handbrake switches etc. as long as they all switch to ground, i.e. the door switch or whatever has one side of the switch connected to ground. The alarm trigger line is now connecting all switches connected to it in parallel so the operation of one switch would effectively work them all so say opening the door would turn on the interior light as well as the boot light and the bonnet light. To stop this, each switch has to have a diode put in series with it so the switch goes back to only operating the light it's meant to but any of the connected switches still trigger the alarm.

[Mephistopheles]

thanks for quick replies!
Regards
Holger

[bitsobrits]

It's a zener werbler. It rectifies the passant signal to the flarad on the warning light.

I was going to suggest it's a low voltage retro encabultor, but upon closer examination I do believe you are correct.

[abowie]

The arrow gives it away.

[Brewer]

I have experienced the same when changing the handbrake switch (see photos). The parasite diode is attached on the positive side of the switch to a braided-looking white on black wire. However, it runs under the LHD driver's seat to an unknown destination and is secured by what appear to be factory-original restraints - metal flaps welded to the floor and under the original paint.

If this is indeed part of an after-factory alarm system, can it be eliminated? Are there other parts of this that need to be exorcised?

[MarekH]

That's a diode. It is there to stop a backfeed of voltage in the opposite direction to the arrow. It is probably part of the seatbelt warning system - look at the s3 wiring diagram on xkedata.com and reconcile the wiring colours.

kind regards
Marek

[Brewer]

Yes, it's clearly a diode and, as installed, would allow a current flow to the powered side of the handbrake warning switch from whatever circuit it is connected to, which would allow that circuit to be grounded as long as the handbrake was on. It would not allow current to flow to the "mystery" circuit. One might assume that grounding this circuit prevents the seatbelt warning light and buzzer from being activated as long as the handbrake is engaged.

Unlike the Jaguar E.165 Repair Manual, the wiring diagram you referenced on xkedata.com does show the circuitry for the seatbelt warning system, but - it does not indicate the presence of any white on black wire, or show a connection to the handbrake warning switch. However, it does indicate a "blocking diode", the only diode shown in either wiring diagram. That, and the direction this wire travels, suggests that this is indeed part of the seatbelt warning system.

Thanks, Marek, for shedding some light on this!

[mgcjag]

S3 Jag service manual 86.65.00......seat belt warning cct diagram B/W from handbrake switch....all details in our Knowledge base section.......Steve

[MarekH]

One might assume that grounding this circuit prevents the seatbelt warning light and buzzer from being activated as long as the handbrake is engaged.

Close, but not quite -sort of the opposite, in fact. The brake float levels and handbrake switch black/white wires remain at 12v so long as there is nothing to ground them. The diode prevents this 12v from feeding into the seatbelt warning system ("SBW") whilst allowing the handbrake switch to ground (and presumably turn off) the SBW independently. Essentially it separates the brake fluid loss and handbrake warning light activation from the SBW and allows the handbrake switch to play a part in both circuits without one triggering the other. This element of the SBW circuit only works if the the handbrake is already ON.

Independence, not conditionality.

kind regards
Marek

[Brewer]

Hmmm - I thought that was what I was saying: Handbrake engaged, both circuits grounded. If ignition is on, handbrake warning light is on, SBW light and buzzer are off. Handbrake off, neither circuit grounded at this point and the handbrake/fluid light is off unless grounded at fluid reservoirs, SBW may be on or off depending on seat occupancy and seatbelt connections.

Regards and thanks again.
Richard

[MarekH]

The chip inside the SBW wants to know whether its pin7 is high or low when it is to apply its simple transistor logic to control the inhibition of the ignition relay, the activation of a buzzer and the lighting up up of a warning light between the dash turn indicators - all of which are differently activated/reactivated.

The use of a blocking relay means two different circuits get to use the handbrake switch. The first circuit is the familiar low brake fluid?/pdwa triggered?/handbrake on? black/white wire circuit. The second is the activation of a relay winding of the SBW relay so a clean ignition fed 12v ("high") signal can be given to the SBW, rather than a potentially muddled black/white wire signal which has a filament bulb between it and the SBW.

https://www.jag-lovers.org/snaps/snap_v ... 1329941230 has the SBW circuit.

You can disable just the buzzer or the ignition inhibition or cut the connection between the buzzer and light by pulling one of the connections at pin10 components internally or by swapping the four white/yellow wires over.

The activation sequence for the SBW is on page7 of the little tan coloured Owners Manual booklet. People converting from lhd to rhd take note. (You can just unplug the damned thing and swap the white/yellow wires.)

If you are really keen, you can make the unique SBW relay out of a 5pole changeover relay by connecting W2 to C3. It just flips a black/white grounding signal into a white wire 12v input for pin7 of the SBW.

kind regards
Marek