Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Alternator Wiring help?

I'm fitting a new uprated alternator and am a bit confused with the wiring in my car!

This is the wiring diagram (from GOMOG). I have a two wire alterantor. There should be a large gauge brown wire that goes to a post on the starter solenoid, and from there another brown wire goes to the ammeter. I have that Brown wire that goes to the Ammeter. The back of my Ammeter has two Brown Wires and two Brown/White wires as per the diagram.



However on mine I have a Brown/White wire that goes from the alternator into car. It then somehow has connectivity with the two Brown/White wires connected to the ammeter but I think the two brown/white wires on the back of the ammeter are a smaller guage. When the thick Brown/White wire is disconnected from the ammeter, the lights and ignition still work fine. When I turn the ignition on, there is 12V at the 'alterator' end of the thicker Brown/White wire.



The current wiring works (as in everything runs and the battery charges OK) although I never get much movement from the ammeter.needle.

I'm thinking that I just create a new brown wire from the Alternator to the starter solenoid post and then cap off the previous Brown/White.

Any thoughts?

On our 1985 4/4 the ammeter is wired through an additional "starter relay" not shown on your diagrams.
The wiring diagram in our car's handbook also shows this relay.
Might this help explain what is going on?

Had a look a the wiring diagram on GoMog and I have none of those relays - completely different system unfortunately.

I'm thinking that the GoMog wiring diagram is actually wrong. From what I'm reading, an ammeter needs to sit between the output wire of the alternator and the battery.

I've looked at an earlier wiring diagram for a dynamo car, and the Brown/White goes from the dynamo, to the Ammeter, and then a Brown goes to the battery terminal Starter solenoid. That mirrors the route my wiring takes (albeit with an Alternator) so seems to suggest that my car wiring is correct.



I think I'll add a couple of extra piggyback wires to and from the Alternator to cope with the increased ampage of the new alternator.

What alternator is it?

Why the upgrade?

Arwyn

The cable you have floating in your lower picture is main positive alternator output usually labelled as B+ on alternator. It should be the thickest one and brown/white in colour. It goes to load side of ammeter with other brown/white wires. The battery side of ammeter has plain brown wires one of which goes to battery via the common connection point of starter solenoid.

If in doubt just remember the battery feeds start system and maybe horn directly and loads (ignition, lights and hazard) via ammeter. If you're unsure of ammeter connections it doesn't matter if you get them the wrong way around as long as all brown go to one side and all brown/white to the other, it will simply work in reverse with regard to charge/discharge.

Smaller brown/yellow wire goes from I or AL connection on alternator to charge warning light of course fed by ignition so it comes on before engine is started. Presence of (3w) bulb is important as it provides initial field current to kick-start alternator once engine running.

Hope this makes sense.

BTW the top picture shows alternator output connected directly to battery so it could not possibly show charge current into battery on centre zero ammeter.

It's a Wosp LMA 259.

Thank you - yes I've come to the conclusion that my car is wired correctly and the wiring diagram on Gomog is incorrect.

When I first had her I swapped the alternator bulb for an LED in error. The correct 3W went back in!

There was a short interim period TBM when alternators were first introduced where they kept the centre zero ammeter. As alternator output currents quickly crept up it didn't take long for them to be displaying off the scale charge currents so they were done away with and alternator output then did go direct to be battery.

TBH loosing the ammeter is a blessing electrically (but maybe not for originality) as bad connections to same won't inhibit alternator charge current.

Yeah, I'd prefer a voltmeter but I don't think there's one that fits into the quadrant gauge.

This is a rare example of the transition to alternator charging. In this case on a later Series 2a Land Rover where the Smiths segmented gauge cluster houses a voltmeter. Probably rocking horse poop category now as alternators were initially an option, but who knows.