Replacing early type 1850 alternator

[dollyman]

HI all,

I am replacing my early 1972 alternater.
I know the large brown wire will go to the large terminal, but there are two smaller wires going back to the loom. One solid brown and one with a yellow tracer. What do i do with these two?

Second question.
Due to multiple snags including a snapped anchor nut on the rad..... And a kenlowe fan in the way....
I cant get the long bolt out. I have come up with an idea of grinding the old alternator off where the bolt goes through, and then cutting a slot in the new one to aid easy fitting without removing the bolt
Has anyone done this? I cant think of any problems as it will be a tight clamp, i was also going to fill the slot with "JB Weld" when bolted on.

Tony.

[MIG Wielder]

The thick brown wire is the main current output which goes to the connector block by the battery.
The thin brown wire on the early Dolomites is the " sense" wire which monitors the voltage at the same connector block by the battery and feeds it back to regulate the output voltage. On later Dolomites it is replaced by a 2nd thick brown wire to carry all the extra current and the battery voltage sensing is done locally at the alternator output terminal .
The Brown / yellow wire goes to the IGN warning light and also provides the initial field winding current when the car is first started.

On MPD my early 1850 I seem to remember cutting the bolt and replacing it with a minimum length of steel studding inserted from the back of the alternator.
HTH,
Tony.

[dollyman]

Hi Tony,
Many thanks for the reply. I should have mentioned that the old alternator had two plugs....
So do i connect the two brown wires together?

Also i have tried threaded rod and also found another bolt the same size, but it wont go through because of the water pump outlet.
I guess nobody has tried my modification or butchery as some might call it So i will give it a go, i thought someone might have tried it.

Tony.

[tony g]

Dont use threaded rod, its usually made from cheese.

Tony

[cliftyhanger]

Tony, High Tensile studding is available, and can be very useful. But it is nowhere near as common as the cheese type. Luckily I have Namricks on my doorstep for emergencies, or fleabay if I can wait a few days....

[MIG Wielder]

Hi Tony,
Many thanks for the reply. I should have mentioned that the old alternator had two plugs....
So do i connect the two brown wires together?
Tony.

Hi Tony, If you have 2 plugs on the back of the alternator then that looks like a very early 15ACR alternator.
I had to refresh my memory on this one but Page 179 of the Haynes manual explains a lot.
One of the plugs has the main + Output and it also looks like a separate earth terminal.
There should be a thick brown wire here which needs to go to the top large terminal of the new 17ACR alternator.
If there is a separate thick earth wire on this connector it can be ignored as the earthing for the new 17ACR alternator is via the casing.
The 2nd connector will have a brown / yellow wire linking 2 terminals. This goes to the lower small terminal on the new 17ACR unit with the 2nd connector wire taped back.
There will also be a thin brown wire on this 2nd connector. This is the original "sense" wire and should go to the middle terminal on the new alternator. This ensures compatibility with early alternators with this Sensing function.
But yes, it will end up going to the same place as the other thick brown wire.
The circuit diagram on page 247 of the Haynes manual explains this as well. Compare it with page 249 to see the later wiring explained.
Tony.

[dollyman]

Hi Tony, Many thanks once again, i did think that was where the wires went, but i just wanted to make sure. Your knowledge of electrics came to my rescue once again. I am hopeless with anything that has wires attached.
I will at the weekend on how and "if" the cutting of the bracket worked.

Tony.

[MIG Wielder]

Hi Tony, I did some measurements on my 1850 ( admitedly a 1977 one ) and came up with the following...
Distance from the front face of the front fixing lug to the rear face of the rear lug = 103 mm.
Now the front lug is 9mm thick.
The distance from the front face of the front lug to the radiator is 105 mm.
So going back to this idea of using studding.
Assuming the dimensions on your car are similar to mine you should be able to cut a length of studding to 105 + 9mm = 114 mm and feed it through the front lug. Then lower the alternator carefully into position with the studding just touching the rad; and the stud should then push through giving (114 - 103mm) divided by 2 = 5.5mm sticking out each side. This should be enough to get a thin nyloc nut on each end of the stud.
I see what you mean about slotting the fixing lugs but the trouble is that if your brand new alternator fails the motor factors may refuse to replace it.
Let us know how you get on.
Cheers for now,
Tony.

[dollyman]

Hi Tony,
I tried the measurements on a piece of "cheese" rod and it was not long enough So, out came hacksaw and file and cut the new one It is now fitted and feels and looks great as you cant see the piece i have cut out But my back has given up now, so i will fit new terminals tomorrow and see what happens and will let you know.

Tony.

[dollyman]

Everything is now done and working Doing it this way is not as i would have liked, but it works and i cant see it causing any problems? But it has saved me a lot of time and expense. Plus you cant see cut unless you go under car

Tony.