I'm re-installing my 5.3L after removing it 6 or 7 years ago....I have this same problem. There are two wires (one definitely is connected to the load dump module) that come down the right hand inner wing, both terminating in smallish circular connectors. I *think* both of these go on the smaller terminal on the rear outer edge of the alternator. I understand the purpose of the dump module and saw somewhere in another post/forum that the other wire is alternator excitation.

Is this correct, do both wires go on the alternator?

Thanks,

Brad
1991 Jaguar XJS Coupe, Classic Edition (now with a 5 speed manual transmission!)

 

These diagrams show the dump module.



One wire goes to ground. According to the diagram they're both black. You'd need to figure out which one so that the diodes are in the right direction.

Cheers
DD

 

What is the purpose of load dump module?

I have never heard of anything like that, or run across anything like that

 

It's a protection device but I've never known the theory behind it nor why the XJS needed one when other cars didn't.

Earlier XJSs, like my '88, had an overcharge warning light. Again something I've not seen elsewhere.

Others will chime in.

Cheers
DD

 

….which (they say) is worth a thousand words!

”G” marks the load dump ground. The connection that I am asking about is aft of the load dump box, marked “??”

 

To my eyes it looks it might be brown/black. If so, that's the exciter wire that goes to the alternator together with the dump module wire

Cheers
DD

 

The alternator load dump system works to mitigate huge voltage spikes that can occur (I've read from 100 - 120VDC! To be fair, these are very short transients, up to 100ms, but still pretty impressive) when the load of charging the battery (or other large load) is suddenly removed. This is done to protect sensitive electronics that would otherwise get fried.

Brad

 

Yes, it IS brown/black.

Thank you, Doug!!

Brad

 

So it acts a bit like a condenser on a points ignition then?

 

Seems like a Lucasism device, to me.

I've seen many otehr cars with alt warning lights, that would illuminate in an undercharge or overcharge condition, but not overcharge per se.

I also see the alternator "seems" to be of a 2 wire variety, rather than three wire, which may ahve something to do with the module, unless the module acts as the third wire.

A typical SI alt I am familiar with has the main power wire, an ignition wire that keeps the regulator inactive during 'off", and a voltage sensing wire that gives a relative voltage from distant source to compare to batt voltage, and adjust output accordingly.

Doug

 

Here is wiring for a typical US alternator and regulator, both external and internal regulation. Note the ext regulated alt has a capacitor

Doug

 

No, it has zener diodes that will conduct at anything over a specified voltage. So any voltage over the zener's spec will be clamped to ground. They are fast so they will/should get rid of any/most transients and protect electronics on the +12V battery power line. They act as a voltage regulator. It looks like the load dump module is kind of a pricey part, >$200 for a used part. If mine went out I would probably buy two 15V zeners from Digikey for about $.13 each and replace the Jaguar part.

 

So, there is no internal voltage regulator on these Jag alts?
Doug

 

They do have a traditional internal voltage regulator.

Cheers
DD

 

The interesting thing is that the Series III V12 sedans, which had the same electrical architecture as the XJS, and were being built concurrently to the XJS, never had the dump module nor the overcharge warning light.

Cheers
DD

 

And the late 6 Litre ones, such as the one whose alternator I'm trying to resolve, don't show mention of a Load dump Module. Presumably everything managed via the internal regulator?

Paul

 

Duplicate. Apols

Paul