MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Alt. conversion, wiring issue?, HELP!!!!!!!!

Dear MGenuises,
I believe I've connected everything correctly, yet once again I'm at one of those familiar head scratching places.
The recipient vehicle is a 79' Ca. MGB.
donor alternator is a Delco/Remy from a 3.8 olds. that was working when pulled from the donor.
Fabricated a working mount, no sweat!
2 large brown wires are connected to the terminal marked BAT.
Small brown w/yellow stripe is connected via spade to the terminal marked 1.
Situation: large brown wires show current when checked against alt. casing with test light, indicating a good ground,
Ignition indicator on dash, shows nothing in the on position.
Car will start and run for 1-2 minutes with a Jump.
( probably just until the battery can't fire the ignition any more ).
Any load on the system I.E. lights, fans,etc. kills the motor immediatley.
The girlfriend has locked the liquor cabinet and hidden the firearms, the dog is eyeing me with thinly veiled distrust. HELP!!!!!!
Sincere thanks as always,
JIM.
J A Kelly

Jim. The first thing to do is to disconnect the battery from the system and charge it. When fully charged, the battery should show about 12.5 volts. You should be able to run the engine on the battery for more than an hour with nothing else draining it.

When the battery is fully charged, check the voltage at the terminals, then start the car. Check the voltage at the battery clamps. You should see at least 13.5 volts and, preferably, 14.5 volts. If not, the alternator is not working, for whatever reason.

The indicator on the dash should come on when the key is turned to the "on" position and you should hear the fuel pump click for a moment. Since the light does not come on, this might indicate a problem in the white wire circuit. The light comes on when there is an unbalanced condition between the voltage output of the alternator and the voltage in the white wire circuit.

I am still quite happy with my Lucas alternators, so can provide no further help as I am not familiar with the hook up of the Delco alternator. Paul Hunt, who is qualified to pass such judgements, has written that the brown/yellow wire is necessary to cause the alternator to start charging properly. You may wish to e-mail him about your problem and see what assistance he may be able to provide. Les
Les Bengtson

Thanks Les,
I suspect that paul will sound in here anytime,
(matter of fact I'm counting on it).
In the mean time I'm going to try your suggestions,
thanks again,
Jim.
P.S did you recieve the pic I sent you?
J A Kelly

Jim,
You might want to also check out this site, by Paul Tegler, http://www.teglerizer.com/alternator/index.html . I don't know if it will be of much value to you, but it seems knowledgable. Also, you might want to write to Dan Masters, a visitor and member here, at dmasters@aol.com as he has done some successful GM/Delco alternator conversions. He has a site here, http://www.vtr.org/maintain/alternator-overview.html
Bob Muenchausen

Jim,
Sorry, I discovered that I had to update my links and address for Dan Masters.

His site is at http://www.vtr.org/maintain/alternator-overview.shtml and his email address is at danmas@aol.com
Bob Muenchausen

Alternative alternators (try saying that correctly after 'one over the eight') have various connections, and the Lucas came in two flavours two. Early Lucas units seem to have had two brown connections - one thick and one thin - and both were necessary as the thick one was the output and the thin one the external 'sense' connection. This connection went to the same place on the solenoid as the thick connection, and was needed to ensure correct operation of the voltage regulator. Without this connection the regulator may well shut down, or possibly give an excessive system voltage. Later Lucas alts had two large output spades, and one thick brown in the harness could go to either, the 'sense' connection being internal (making sense ...). Late model cars had two thick browns in thre harness and this was to give a higher current capacity and lower volt-drop under heavy load conditions. All the Lucas alts need the brown/yellow indicator wire on (usually) the smaller third terminal or the alternator may well not start charging. The alts on both my cars 'kick-in' without this connection at about 3k rpm and then charge normally down to about 600 rpm, but it is possible that a brand-new alt out of the box may not do this. The AC Delco used on the factory V8 is the same, but a GM Delco with a BAT stud and two smaller terminals is like the earlier Lucas units in that the BAT stud is the output, one of the other terminals is the sense connection, and the other the indicator. At least one web site (not those listed above) claims that the sense terminal is the indicator terminal, and that *neither* need be connected, making the alternator a truly 'one wire' unit. This isn't the case.

Certainly either the battery must be charged until it can start the car, or the jump leads and donor car left connected after starting until the cars battery has gained some charge, before you do voltage tests or add any additional loads. If your alt has the BAT stud plus two additional connections then maybe one of them has to be linked to BAT, and you have to get this link and the indicator wite the right way round. You can check the indicator circuit by grounding the brown/yellow (NOT any brown wires) with a battery with some charge connected and the ignition switched on and the warning lamp should light. If not, check the bulb, and that you have 12v on the white at the bulb holder as well as the ground on the brown/yellow.
Paul Hunt

Thank you Paul,
If you have not already, you should start writing a
book, I'll let you know the results,
as always you are ( along with Les and Bob ) the
voice of calm and reason.
thank you again,
Jim.
J A Kelly

Jim,
If you're using the Delco 10si or similar, the small input terminal #1 needs to be hooked to switched 12v power and terminal #2 needs to be hooked to full time 12v as this is the sensing lead which goes directly to the internal zener diode within the alternator and determines how much output voltage the alternator will produce based on the voltage at this terminal. Not hooking it up will give you zero output. The simplest method is to simply make a small wire connection from the B+ terminal to the #2 terminal. I did this conversion on my B years ago and it worked flawless. Much more current than the original Lucas and inexpensive too. I got a lifetime warranteed model at Autozone for $38. 65 amps.

Scott
Scott Wooley

Jim. No, I did not get the photos. I use the Aztec server exclusively for this website and it is very primative. No photos or attachments. You may find my website, www.custompistols.com to be of use to you. It has most of the tech articles that I have written and some by other people covering areas in which I have no signficant competence. David DuBois's tech article on the SU fuel pump is of significant value to any of us running the SU pump. If you contact me though the website, photos and attachments are functional. This would allow you to send me a picture of your car and me to transmit any photos which may be of use to you. Les
Les Bengtson

I thought i sent this out earlier, guess the ol' dial up failed......

Scott!!!! your the man!!!
car is charging happily now, if you don't mind I'm going to "RE-THREAD" this info so that others will more readily get the benefit of it without all the trial and error. Also plan to take some photos of my
mounting system, Essentially a steel plate with a hole in the middle, on the rim of this metal doughnut are three ears, 12 o'clock, 6 o'clock, and you guessed it roughly 5'o'clock. saves one from having to remove or neglect the original mounts.
Thanks Scott!
P.S. Girlfriend and dog are speaking to me again
JIM
J A Kelly

Scott,
Glad to hear yours has given you good service. Got any words of wisdom about the best way to mount it?? As you may know, there has been more than one fountain of knowledge on this aspect of using the 10si, and not all have proven as good as others. What is your recommendation for just the mechanical mounting given your success?? It would be a particularly good service to those who rather use this unit.
Bob Muenchausen

This thread was discussed between 09/04/2005 and 12/04/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.