On 14 Feb 2006 06:05:32 -0800, "cmackay"
wrote:

Does anyone have a wiring diagram for converting an old tractor wiring
system from 6v (dynamo) to 12v (alternator)?

Charity shop, get a Haynes manual for anything '70s - preferably
something with the same maker of alternator. Just copy it.

Lucas alternators are rubbish. Fit a Bosch. Japanese alternators are
great, but not weatherproof.

It'll be negative earth afterwards and it might have been positive earth
beforehand. If you replace both battery and dynamo/alternator together
then you've sorted it out anyway. Ammeters and voltmeters might care
too, other gauges generally won't.

Alternators come in two sorts - regulators inside, or separate
regulators. Nearly all of them outside the USA are external. The
installation difference is trivial (one extra wire). Regulators aren't
interchangeable, so keep the one that came with the alternator. Replace
the wire between alternator output and battery with something suitably
heavy (recycled from the donor car might work, if long enough).

Wire the charge warning light according to the alternator circuit and
use the right bulb. If it's an old Lucas ACR alternator, then this bulb
is a crucial part of the circuit and _must_ be the right rating!
(usually in a red holder in the dashboard, not black or white like the
rest).

Discard any ammeter. Add a voltmeter if you wish (more use with an
alternator).

Electronic rev counters (which I doubt you have, unless it's a Yank)
need replacement.

All bulbs change to 12V, as does the indicator flasher (if fitted).

Dashboard fuel / temp gauge might need replacement, or else a solid
state regulator (a 7905 and a couple of resistors, AFAIR) added to its
existing voltage regulator.

The ignition coil should be replaced, which is probably a good thing
anyway. Don't use a ballasted coil where there's a resistor in the feed
to it (or a Ford coil).

Diesel pre-heaters can be left alone, but don't leave them on too long.
Replace them with 12V if you do break them.

The starter can stay, but you might change its solenoid (it may not even
have one on a tractor, and I assume it's a helix not a pre-engaged
starter). Or else just ignore it and fix it if you break it. Ford used
to be the easiest source for a separate solenoid, as they kept using
them for longest.

Vehicle Wiring Products (webbable) are your best source for parts. Get a
decent crimp tool for non-insulated crimps and don't use the
pre-insulated sort if you care about reliability. Some silicone grease
too.


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