• Hi Guest! Being a Paying Supporter is NOT a requirement to participate at BCF. However, subscribing will help ensure we can continue to serve the LBC community for years to come. If you enjoy BCF and find our forum a useful resource...Please consider supporting us by **Upgrading**
    (PS: Subscribers don't see this banner)

Wiring question for alternator conversion


Jedi Warrior
Country flag
I'm hooking up a one wire alternator and I'm eliminating the control box from the firewall. It seems to me that I need to tie the 3 brown wires together. I think I can delete the field wire (yellow and green) altogether. I am a bit confused about what to do with the 2 yellow wires that connect to terminal "D". I am not going to use any warning light.


Country flag
I have a 3-wire, but think at a minimum you can do this:
Leave the small yellow and yellow/green disconnected. Use the large yellow as your alternator wire, connected to the 3 browns at the firewall.
One friend has done this and has inserted a 25 amp fuse between the large yellow and 3 browns.

Personally, I didn't think the large yellow was beefy enough and ran a 10 ga red wire from the alt to the starter solenoid hot post. But the friend hasn't had problems with his setup.


Darth Vader
Country flag
Here is the drawing that I drew after I did my BJ7. A couple corrections you should notice. 1. is that where I labeled a wire at the alternator as yellow brown is actually yellow/green. 2. Also just ignore the the insertion of the amp meter. But do use the #10 red wire from the alternator to the solenoid ( this is your most direct path for charging current back to your battery).
The two wires that were connected to the "D" terminal of the voltage regulator are the wires for the warning light. ( should be yellow ). As I look at my drawing I realize that I reversed the labeling on the yellow and yellow/brown wire from the alternator. But you can eliminate yellow and the yellow/green wires on your regulator terminals of "D" & "F" since you are using a one wire alternator.
But make sure you do not have any hot wires hanging under your dash because the other wire at the old warning light location is coming from your ignition switch and should be white. Sorry for the confusion in colours but the drawing works. The terminal switch is in place of the voltage reg.


  • img182.jpg
    25.1 KB · Views: 49


Darth Vader
Country flag
Just some comments about the use of one wire alternators verses the 3 wire set up. From my studying this over the years I have read some people with 1 wire alternators, this includes this use on many makes of cars besides Healeys, have reported an inability to keep their batteries well charged. I believe the reason for this is the nature of the way the 1 wire alternator senses the voltage in the system. It's sensing ability is off of the field terminal of the alternator. In a 1 wire alternator there is an internal jumper between the battery terminal and the field winding. Which means the alternator senses its own voltage which is always good if the alternator is working correctly. Because it always sees good voltage it doesn't always charge strongly enough to recharge the battery fully. In the 3 wire alternator the field terminal is connected over in the wiring harness closer to the load. Either at a voltage regulator terminal or at some point common to the power parts of the circuit such as a terminal in my drawing. Since it is connected where is will sense the effects of load currents it also senses differentials in voltage drops hence it sees lower voltage which then tells the alternator to charge more. So the 3 wire system has a better ability to keep the battery fully charged.
Just my take on the two different systems. Dave.
Similar threads
Thread starter Title Forum Replies Date
T TR2/3/3A Question on wiring Denso alternator through ammeter Triumph 4
N Spitfire alternator wiring question Triumph 1
bash Alternator wiring question Triumph 5
E BE Alternator Wiring Question Spridgets 5
T TR4/4A TR4A alternator conversion wiring question Triumph 28
Webb Quick Alternator Wiring Question Triumph 3
LastDeadLast Bosch Alternator Wiring Question Triumph 1
nichola TR6 Question on new wiring harness Triumph 6
J TR6 73 TR6 Temp Gauge Wiring Question Triumph 6
JPSmit Todays question - wiring Spridgets 14
ckeithjordan TR2/3/3A Wiring Harness Question[s] Triumph 10
C MGA Wiring harness question MG 6
Michael Oritt LED bulb/resistor wiring question Austin Healey 24
G TR4/4A Front Parking Lamps Wiring Question Triumph 5
Griz Trafficator Wiring Question Austin Healey 16
Michael Oritt Wiring question Austin Healey 5
Got_All_4 TR2/3/3A Quick Overdrive Wiring Question Triumph 6
K TR2/3/3A Another question about pulling the wiring thru the stator tube... Triumph 15
J TR6 '73 TR6, Wiring Question. Original Owner Triumph 5
AngliaGT '74 Midget - Wiring Question Spridgets 2
Willie_P TR4/4A WIRING question: gear reduction starter Triumph 3
B Question about Dual Polarity Electronic Fuel Pump - How to Connect Wiring? Austin Healey 9
TomChar TR6 '74 brake failure / oil pressure / ARV wiring question Triumph 19
B TR6 Wiring question Triumph 11
Tinkerman TR2/3/3A Front turn signal wiring question on my post 60000 TR3A Triumph 8
D Original BN6 / BN7 Battery Switch Wiring Question Austin Healey 15
T BN-1 Wiring Question Austin Healey 3
Griz Rear Wiring Harness Question Austin Healey 6
Griz Another BJ7 Wiring Question Austin Healey 4
M Quick tachometer wiring question on a '65 Spridgets 10
Tugboat Wiring Question Triumph 6
glemon Wiper Motor Wiring Question Triumph 11
B Another wiring question 57 smallmouth control head Triumph 2
B Question on OD wiring harness 57 Smallmouth Triumph 15
Tinkerman TR2/3/3A Wiring question TR 3A Triumph 4
T TR4/4A White wire question on TR4A A-type wiring Triumph 2
Tinkerman TR2/3/3A Wiring question TR3A Triumph 5
M_Pied_Lourd TR2/3/3A TR3A Gauge Cluster Wiring Question Triumph 7
R TR2/3/3A TR3 Headlight Wiring Question Triumph 6
R Wiring question. No spark, need help. Spridgets 16
Coyote1 Overdrive wiring question Triumph 8
T Wiring hack - iginition switch question Spridgets 8
B wiring harness question: Triumph 3
hondo402000 TR6 Another TR6 wiring question Triumph 5
hondo402000 TR6 TR6 Wiring/amp gauge question Triumph 8
T OT Wiring question - but probably useful to know Triumph 10
Tinkerman TR2/3/3A Wiring Harness Question on my TR3A Triumph 8
H Wiring question? MG 16
jaegzie Wiring Question Spridgets 16
mountainman TR2/3/3A TR3 Tail Light Wiring Question Triumph 5

Similar threads