• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)

Alternator Swap

Share this page

Dugger

Dugger

Senior Member
Offline
I may have messed up, but I had real good intentions. My OE Lucas ACR17 had a serious squealing front bearing, so I decided that I would rebuild the unit, but until I could get to that little project, I would install a "modern" alternator for the meantime.

I picked up a Motorcraft unit and with a little work got it mounted nice and straight. No problem really, just a little boss grinding here and there and another adjustment arm from an parts store and walaa, modern alternator installed.

Here is where it gets dicey, I connected the 10ga. brown/yellow lead to the "BAT" terminal, discarded the looped 14ga brown/yellow leads (actually left them in the plug for the Lucas unit), connected the brown lead to the "FLD" terminal, and sealed the other brown/yellow lead with heat shrink. I also connected the black ground lead the the "grn" terminal for good measure.

I reconnected the battery and turned on the ignition switch, the ignition light did not come on (?), and when I started the car the amp gauge pegged out of site on the '+' side. While the car was at fast idle (1300rpm) I took a digital VOM and checked the voltage output of the alternator - 18.9 volts. Then I checked the voltage at the "FLD" terminal - 15.9 volts @ 1300 rpm. Mind you the amp guage is still pegged.

I shut the car down and felt of the "BAT" lead wire from the alternator, to my suprise it was not even very warm - I just knew I was going to be running for the fire extinguisher.

So now you have the background....what did I do wrong?

Why didn't the ignition light come on when I turned the ingition key to the 'on' position? (btw-the oil pressure light did illuminate)

Why did the amp guage peg to the '+' side and stay there?

Is 18.9 volts a normal output for a 55amp alternator? or can the internal regulator be bad?

Does the 15.9 volts at the "FLD" terminal tell me anything?

Any help will be greatly appreciated
 
Something sounds weird about those high numbers. I don't doubt you, they just seem way to high. Does that unit have an internal voltage regulator? It sounds like there is a definite problem there.
 
Voltages are way, way high !
Since my Motorcraft is externally regulated, my first guess is that yours is too. The "FLD" label would tend to indicate that as well. Is there also a "STA" terminal ?


BTW, brown/yellow is the wire to the dash lamp, so it's no surprise it didn't come on /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
There is another terminal on the alternator, but it is not labeled. The NAPA guy looked it up and said this was an internally regulated unit. The regulator may be bad.

I should have known better than to trust a counter clerk. I went to the NAPA website and looked uop the alternator, and guess what, it is NOT internally regulated.
 
If the Motorcraft unit has a "FLD" terminal marked on it, it is an externally regulated unit and will not work.

If the back looks like this, then that is the early externally regulated unit.

You might want to try a Delco Delco 10SI (7127) set at the 12 or 9 o'clock position as long as you're willing to modify the drive end housing some. The Tinster even has one on his car. It's one of the items that hasn't given him problems. The one in the picture is at 3 o'clock, determined by where the plug goes in relation to the adjusting ear. The 10SI is a robust unit available anywhere and relatively cheap.
 
Or, you could buy the appropriate regulator for your Motorcraft. It's also robust, cheap, and readily available. But makes for another box to mount somewhere.
 
Back
Top