Subject: Time:12:35 PM
OFFICE MEMO FAQ on Pos-Neg Conversions Date:11/4/94
How about a FAQ on converting cars from positive ground to negative?
I looked on triumph.cs.utah.edu and I didn't see a FAQ on +/- conversions.
Since this seems to be a frequently asked question, it occurred to me that we
ought to write a FAQ on the subject. How about if I compile comments from
anyone who wishes to contribute? Send comments directly to me,
<reilly@admail.fnal.gov>, cc to the list only if you think it's worthwhile.
First draft outline follows:
Converting 12-V Positive Ground (Earth) Cars to Negative Ground
Version 1.0 (draft)
1. What cars does this apply to?
AC thru year .........? model names could also be listed
Allard thru year.........?
Alvis thru .........?
Armstrong-Siddeley thru .........?
Aston-Martin thru ......?
Austin thru .........?
Austin-Healey thru .........?
Bentley thru .........?
Berkeley thru .........?
Bond thru .........?
Daimler thru '64 (all with generator)
Doretti thru .........?
Fraser Nash thru .........?
Healey thru .........?
Invicta thru .........?
Jaguar thru '64 (all with generator)
Jowett thru .........?
Lagonda thru .........?
Lanchester thru .........?
Land Rover thru .........?
Lea-Francis thru .........?
Lotus thru .........?
MG thru .........?
Morgan thru .........?
Morris thru .........?
Nash-Healey thru .........?
Reliant thru .........?
Riley thru .........?
Rolls-Royce thru .........?
Rover thru .........?
Standard thru .........?
Sunbeam thru .........?
Triumph thru .........?
TVR thru .........?
Vauxhall thru .........?
Wolseley thru .........?
2. What reasons are there to convert?
A. Permit use of a modern 12v neg ground radio
B. Ignition coil provides a better spark
C. Use of an alternator
D. ?
3. Arguments against?
Positive ground = less corrosion at the battery terminals (this is just
something I've heard, can anyone confirm whether it is true?)
4. Do the following components (if the car has them) need to have the
polarity switched?
ammeter - yes, switch the wires on the terminals
battery voltmeter - yes
clock - no
coil - no, leave terminal CB or "-" to the distributor, because in every coil
the primary winding is from SW to CB or from + to -, the secondary winding is
from CB or - to the center tower. By connecting a coil in this fashion, the
CENTER electrode of the spark plug will assume NEGATIVE polarity. The center
electrode of the plug is always hotter than the side electrode. Since it
takes less voltage to cause electrons to move from a hot to a cold surface,
current flow must be from the hot center to the cooler side electrode. If the
coil is connected wrong 20-40% more voltage will be required to fire the
plugs.
distributor contact points - no
distributor capacitor (condenser) - no
electric fuel pump
SU electromagnet & diaphragm type - no
Lucas motor type - ?
electric window motors - no, easier to reverse wires on the switch
fuel gauge - no
generator - must be repolarized, touch the cutout contacts in the
voltage regulator together.
heater fan motor - ?
horns - no
ignition switch - no
light bulbs - no
light switches - no
oil pressure gauge/light - no
overdrive solenoid - no
overdrive switch - no
radio antenna (motorized) - ?
relays - no
starter motor - no, because it is a coil wound motor
starter solenoid - no
starting carburetter solenoid - no
tachometer (electric) - ?
trafficator/semifores - no
turn signal flasher - no
voltage regulator - no
water temperature gauge/light - no
windshield washer pump motor - yes
wiper motor - no, except self-parking type
This is just a first draft. Comments are solicited wherever I have put a "?"
or if you disagree with my comments.
Reply to: reilly@admail.fnal.gov
I have two positive ground cars, but I have not converted either one yet.
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