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MG MGB Technical - Alternator Conversion

What is the best and easiest alternator conversion for a 74-80 mgb?
Tom Trepac

It's the Delco/Saturn unit. Go to

Tons of amps, inexpensive, readily available, and with one easy mod, it's physically interchangeable with the Lucas.

Happy New Year!
Allen Bachelder

I just completed the Delco/Saturn conversion. All went well, I did have to grind a small amount off of the back side of the two top mounting ears in order to get it to line up properly. Also had to find a slightly longer belt.
Bob R.

The easiest one is the Bosch alternator conversion. Stock plug in the wiring harness plugs right into the
Bosche alternator.

Quick question about the Delco/Remy alternator. Can you retain the ignition warning light?

If so what is the correct wiring, as the plug has a different number of wires coming from it compared to the Lucas plug and loom.

I have the D/R Alt fitted in my 71 GT and it kicks out a full 96amp but I haven't found way to achieve the ignition warning light or see how its possible, help!!
K Harris

I put the Delco/Saturn in my 74 MG following the connections in the article referenced above. The light is operating correctly and goes out just above cranking speed when starting the engine. I had no interference with the mounting ears and was able to use the same belt and the belt tension adjustment link.

Janson Hurd

Thanks to international NON-standardisation, the Delco/Saturn alternator isn't easily available in NZ, sadly...however there are other almost-bolt on Bosch alternatives.
Curtis Walker

Unless you have lots of extras a godd condition original spec alternator works very well!! Why are you wanting to change?

67 BGT - with alternator from 70 BGT
I D Cameron

Some Delcos are self-exciting and don't have provision for a warning light connection, in which case the only (sensible) alternative is to fit a voltmeter. Other Delcos are *not* self-exciting and unless a warning light is connected they wont start to charge until the engine is revved significantly, if at all. In those cases a voltmeter won't help.
Paul Hunt 2

Thanks Paul, that was the option I was thinking about as a way round the problem.

Iain, I have 100w80 headlights plus 4 Cibie 150w spots plus other toys. The Prince of Darkness was struggling.
K Harris

You can buy a brand new Lucas very resonable. They are reliable as can be and are a direct replacement. Why go to something that requires mods. Unless that is your running a/c. Bob
RHT Thompson

Depending on the amps you need, there is a somewhat less powerful conversion you could do which has been successful for many years and your can find info on it at this site: . It is in many ways similar to the Saturn/Delco (actually a licensed Bosch unit) but without the need to "re-clock" the body and pretty much a direct bolt-in replacement. It puts out about 55 amps, the Saturn unit about 95 amps. The Fiesta Bosch swap is a good one for a standard use B's which used the early 16AC, 16ACR Lucas alternators or earlier generators. FYI
Bob Muenchausen

To add to Bob Thompson's comments, a Lucas 18ACR alternator is just as good a replacement for earlier low powered Lucas units as the Fiesta Bosch or the Saturn unit if you don't need the amps. Proper fit, only minor alterations to the wiring if you have a generator or 16AC or 16ACR Lucas alternator and you get to retain your British motor heritage.
Bob Muenchausen

New fan belt.

Dan Robinson

My local auto-electrician / alternator repair guy reckons the new Lucas units are bollocks and wouldn't sell them because he didn't want to deal with the returns.

That's his word only, of course, and I wouldn't want to start viscous rumours! :)
Curtis Walker

The Moss supercharger system comes with a new Lucas alternator. I've been running mine since 2003 and have had no problems. Ray

A Lucas Alternator can be good, the OE unit I had looked as tho it had been on the car since day one when I bought it and the brushes at the commutator looked as tho that could be true! I replaced that unit, after some 1987 rehab, after 22 yrs when it finally decided to die from a terminal field coil winding short.

I replaced it with another which did fine (except that it was too under powered {it was a 16AC unit, 35 amps} ) to meet my needs on winter evenings (too high a charge speed required to fire it up at idle), that is why I replaced it with a Ford Fiesta Bosch unit of 55 amps back before there was a Saturn unit conversion to be aware of. The Fiesta conversion was done in 1999. It (and the Saturn) had the advantages of more output power AND a much lower rpms requirement to energize the unit for charging making it (them) much better suited for meeting needs when all electrical units were on.

I have been told, however, that even Lucas finally recognized this problem and corrected both of these problem areas when they introduced the 18ACR unit on the latter MGBs.
Bob Muenchausen

I made the Delco/Saturn conversion after switching out Lucas alternators five times in two years.

Knock on wood, so far so good. Ignition light works as it's supposed to and electrical system has plenty of power. Reclocking was not a big deal.

And in the U.S., the Delco/Saturn alternator is more readily available over the counter than the Lucas should I have to make a switch while on the road.

My 2 cents worth.

Ken V.
'77 MGB
Safety Fast!
Ken Vandruff

If I recall correctly, there is a substantial binding post of the back of the Saturn unit, to which you connect the heavy #10 brown wires leading to the solonoid ( (one is a duplicate of the other anyway), using ring connectors. The plug-in wiring pigtail for the Saturn has a red wire and a black wire. Connect the red wire to the MGBs brown-yellow (that's for the idiot light), and the black wire is not used. Make sure the alternator mounting surfaces are clean and shiny so it is well-grounded. I put an additional ground strap on mine - running to a fender bolt - just as a precaution.

Also, if you're counting on all those glorious extra amps, you better run at least one additional #10 from the alternator to the solonoid, and a second directly to the fusebox - to supplement the browns. Between my halogen headlights, A/C compressor and fan, and two additional electric cooling fans, I'm using quite a few of those amps, but they wouldn't do me much good if I couldn't get 'em to the fusebox.

Allen Bachelder

' Forgot to add that I did add a volt meter to mine and, with all the extra electrical loads on my system, it's one of the most useful gauges I have.

FWIW again,
Allen Bachelder


I run my halogens directly off the alternator post (via a heavy duty headlamp switch/fusebox, of course!). Your point about an extra fat wire from solenoid to alternator is well valid!
Curtis Walker

This thread was discussed between 30/12/2006 and 04/01/2007

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