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MG TD TF 1500 - General Electrical Question

This is for a B but it's a generator question so it applies to us T guys just the same. Why not post it to the B forum you ask? I like the wisdom over here.:-)

I've been working on this '65 MGB, converted it to Neg ground, did all the right stuff. Polarized the Genny as described. When I start the car, the ignition light stays on dimly until I give it gas and it goes out. Charging right? Wrong. It is not charging. I had it out on about a half hour drive and when I got home it was dead. Regulator, battery and generator are all new.

There is a MOSS Motors youtube video describing how to check the generator and the regulator. I have tested the generator in this manner and the meter is not climbing but descending. So this tells me the Generator is NG right? Wrong. I have three other gens and one is in another car and is also new and is known to be charging it's system. I performed the same test on all gens and the meter shows it descending.

If the generators are all bad (unlikely) then moving on to "Testing the Regulator" video seems pointless. Also before you ask I tried different regulators with the same result. According to the owner the charging system was fine.

I have looked at Dave D's site but I was swayed by evils of simplicity from the video and it seems so easy. I did however make a neat little jumper (see pic) to connect the terminals on the generator, added a lead to ground through my meter and held the revs to around 1000. My meter only has a 2v, 20v or 200v setting and at 20v she was at around 16.00. If I gave her some gas it climbed, it I let off it decreased. My assumptions were that with this test the Generator is good. The 2nd part of Dave's article is testing the Reg, but it states, "Connect the multimeter between the D terminal and start it up." Between the D terminal and what?

What gives with my Generator?regulator? Any clues guys?

Vince


vping

I don't see where you say you polarized the generator.

Jim Northrup

I polarised it as I've done 3 times before. By the meter going down could it be it's not polarised?
vping

I know it's going to be a PIA Vince but give us the step by step of the process and lets see if we see any errors.
LaVerne Downey

Vince - Thanks for calling my attention to the omission in the procedure to check the generator. That sentence should read between terminal D and ground.

Now, what Kind of a meter are you using? If it is a digital meter, that could well be part of your problem. Digital meters meters can do some strange things, but the biggest problem is that they don't display continuously as an analog meter does. Instead, they sample the voltage for a short period of time and then display the result while again sampling the voltage, the display then jumps to the level of the last sample and so on. Instead of seeing a needle swing up as the voltage climbs, the display jumps to successively higher samples and you don't see what is taking place between samples. If you are not using an analog meter, I would suggest that you pick one up at Radio Shack, Lowe's or Agent Orange.

Your statement that the voltage decreases with increased engine RPM would indicate that you have not gotten the generator polarized correctly. Are you touching the wire from the battery terminal to the smaller of the two terminals of the generator? If not, then the polarity of the field pole pieces are not being magnetized in the correct direction. Cheers - Dave
David DuBois

Ok Here is the abridged version.

Disconnected Battery
Disconnected Generator
Disconnected Coil
Disconnected fuel pump

Replaced fuel pump with a Negative ground facet
Added Negative ground pertronix
Reconnected coil, reversing wires and added two new wires for Pertronix

New wires, rotor, cap, plugs.
New Generator belt - .5" play.

Removed Tach.
Reversed loop in white wire - did this by cutting and crimping with solderless terminals.
Un-soldered green wire and resistor inside of tach and reversed their locations. Re-soldered back in place.

Re-attached a bunch of wiring that had not been connected. Mostly dash lights. There is a spare white wire which was not connected to tach which turned out to be hot and controlled the gauge lights so now there is a white spare under dash not hot. There is also a brown (not hot) and a yellow (OD) which are the only two not connected and right above the steering column.

Reattached Brown lead to Generator. Connected a jumper to the brown terminal on the fuse block and flashed the other end to the smaller terminal on the generator. Polarized at the Generator and not at the regulator.

Reversed the leads to the battery. She fired right up. Tach not working is THE only thing I can find electrically wrong. (other than the Generator not charging) Someone said the early Tachs and Pertronix don't mix. Is this true?

Things to note. One of the first things I did was to fix the horns that were not working. Horn was loose and grounding at the grille. Also at one point I had no headlights and the ground wire up under the right side of the dash by the wiper motor was disconnected. This ground wire was found after I found the generator was not charging. At some point during the testing I also found that the fuse block was cracked so I replaced it. Nothing was effected by this during this adventure.

I replaced regulators several times and nothing changed. I noticed the ignition light on the tach slowly goes out when I give it gas. When I tested the generator ala Dave Dubois, I noticed it is on during the test.
vping


Reattached Brown lead to Generator. Connected a jumper to the brown terminal on the fuse block and flashed the other end to the smaller terminal on the generator. Polarized at the Generator and not at the regulator.

Reversed the leads to the battery


If this was the exact order in the process Vince, I'd say you polarized the generator back to positive ground. Just for kicks do it again. That would also explain the dead tach.
LaVerne Downey

I would be careful with the Petronix... I know one wrong hookup and they are burned out (so I have heard)...you might disconnect it before doing anything more?
Someone with experience with them might chime in....?
gblawson(gordon- TD27667)

You can polarize the generator with everything disconnected.
Just for your info, I have a B gen. on our TD I'm finishing.

1. I would disconnect both wires on the generator;
2. Fire up engine;
3. Take a wire and touch it from battery + post to the smaller field terminal on the generator for a second.

This will maximize the correct flux across the entire armature and switch the residual magnetism to your favor instead of working against you.

I'm sticking on a clear regulator off of an Edsel that says it automatically polarizes. Time will tell!
Jim Northrup

Vince, it was necessary to connect the battery terminals before 'flashing' the generator. The brown terminal on the fuse block is not 'hot' unless the battery is connected (both sides). Bud
Bud Krueger (TD10855)

My bad. When I started writing this my thought was that this exercise started and ended with the battery. I did in fact polarize after I re-connected the battery. I'll have to try Dave's recommendation and report back.
Vince
vping

This thread was discussed on 22/06/2010

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