Lotus Elan

Alternator issue

PostPost by: gjz30075 » Sat Mar 14, 2015 5:18 pm

I don't want to steal jbeach's thread title of "alternator wiring mystery" but that's exactly what I have.

I've had rdent's alternator on for about twelve years. Attached is the wiring diagram that he includes.
Pretty simple and has been trouble free. Recently, my ignition light wouldn't go off. I took the alternator
to my local rebuilder and he says the regulator is blown. He puts in a new regulator and I install the alternator on the car and ..... the ignition light won't go out.

I bring the alternator back to him and he tests it in front of me and it works, and it puts out his test ignition light.
I reinstall the alternator and my ignition light remains on. I take the alternator back to the rebuilder and he
installs another regulator of a different type. One that has two spade connectors instead of three. It, too, fails on the car, ie, the light doesn't go out. I also find that the alternator is not charging. I removed the RB340 regulator, thinking it's backfeeding some circuit but that didn't change anything.

So I go to my local auto parts store (Napa), buy another reman alternator of similar type, from a Chevy Sprint, late 80s. Same configuration of case and three spade connectors. I install it and it, too, doesn't put out
the light and doesn't charge.

I now find that if I remove the wire (of the loop) from the 'light' spade connector, the alternator charges, but,
of course, I have no ignition light. If I remove the wire from the 'ig' spade, there is no change, ie, light remains on and alternator is not charging.

So, what is keeping my ignition light on and charging not happening?

Car is a Federal '72 Sprint and my S4 diagram is slightly different from the car.

A knowledgeable MGB buddy says there is a diode that's blown in the 'fasten seatbelt' circuit (which I have) but
I certainly can't find any diode.

Any ideas??

Thanks
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alternator.jpg and
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PostPost by: gus » Sat Mar 14, 2015 7:46 pm

When the car is running and the alternator is charging, there is supposed to be 12 volts on both sides of the ignition light, meaning it is off. In this condition the 12 volts from the light is supplying the regulator with power

when the alternator is not charging then the L terminal is grounded by a transistor and the light comes on.

the alternator charging with the L terminal disconnected, yet not charging when it is connected, and the light glowing certainly implies a bad regulator.

With the ignition on and the alternator br/ye wires disconnected from the alternator, check the voltage on that wire. It should have 12 volts. Your symptoms imply it may be grounded, but I am not sure
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PostPost by: gjz30075 » Sat Mar 14, 2015 8:17 pm

gus wrote:With the ignition on and the alternator br/ye wires disconnected from the alternator, check the voltage on that wire. It should have 12 volts. Your symptoms imply it may be grounded, but I am not sure


Gus, just to be clear, the brown/yellow wires are the 'loop' connecting the 'I' and 'L' spades, along with one brown/yellow wire going to the ign light. I disconnected those wires from the alternator and with the key on (and the ign light on, curiously enough), I get 3 volts on that looped wire.

The brown/white wire is 12 volts constant, as it should be.

Edit: I just pulled the br/ye wire off the RB340 box and now get 12v and NO ign light. Interesting, I thought the
RB340 box was simply a junction box and it's always been connected to the WL tab. Hmmmm,,,,,
Last edited by gjz30075 on Sat Mar 14, 2015 8:29 pm, edited 1 time in total.
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PostPost by: gus » Sat Mar 14, 2015 8:28 pm

that is your problem

you should have 12 volts, chase it back and see why
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PostPost by: gus » Sat Mar 14, 2015 8:30 pm

There should not be much going on in that circuit, it is possible there is simply a short. try pulling the lampholder right out of where it is and check again
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PostPost by: gjz30075 » Sat Mar 14, 2015 8:53 pm

Well, back to square one. I edited my previous post

Edit: I just pulled the br/ye wire off the RB340 box and now get 12v and NO ign light. Interesting, I thought the
RB340 box was simply a junction box and it's always been connected to the WL tab. Hmmmm,,,,,

So, I do get the 12 v at the light connector. Very difficult to pull the ign light but I can see the light socket and the white wire and nothing looks amiss here. The white wire goes into a 4 way connector which I think goes back to the ign switch.

So, I'm back to a charging system IF the wire is pulled from the 'L' spade. No ign light, of course.
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PostPost by: gus » Sun Mar 15, 2015 11:33 am

So where do you get what voltage? When you disconnect the wire at the control box, what is the voltage on the control box terminal?
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PostPost by: gjz30075 » Sun Mar 15, 2015 12:16 pm

Gus, there is no voltage at the control box spade for WL. The two wires that connect to WL per the diagram are no longer connected to the WL tab but now simply connected together. I do have 12v on that wire with the key on.

I'm measuring 12 volts at the end shown in the pic. This is the end that is pulled from the L spade on the alt.
The other end (of this loop) is still on the I spade. I also have 12v at the connection of the two wires that used to be on the WL spade of the control box.
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PostPost by: gus » Sun Mar 15, 2015 2:07 pm

Ok, you are losing me


The voltage for the wire you picture is supposed to come from the warning light. 12 volts is supplied to the warning light, it travels through the light[a current limiting resistor for this conversation] out to the old control box. From the control box[with no other intermediate connections, no other wires on the tab] it should connect to the br/ye wire going to the alternator.

If you are saying that there is 12 volts at the alternator terminal, with no wire connected to it, then I think something is wrong with the alternator[although I am not entirely sure]

If you are getting 12 volts from some other source than through the warning light, then there is a wiring issue
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PostPost by: gjz30075 » Sun Mar 15, 2015 2:57 pm

Gus, sorry for the confusion.

I have 12 volts at the wire end that is circled in the picture, with the key on. I just measured the alternator spade, to which this wire would connect, and there is .3 (point 3) volts, with the key on. Ignition light is NOT on. With this wire connected to the alternator, the ignition light comes on, but then remains on throughout revving and there is no charging from the alternator, measured right at the alternator.

With this wire disconnected, as seen, charging is happening thoughout revving but no ignition light.

Also attached is a picture of the wire from the alternator connected to the wire from the ignition light. The
control box is no longer in play. In past, for 12 years, these two wires were connected to the WL spade of the
control box. Now, it makes no difference in the symtoms if the WL spade is used or not.

Hope this helps, sorry.
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PostPost by: gus » Sun Mar 15, 2015 3:49 pm

I am still not following exactly when voltages are happening where

One thing first, check the ground side connections. Make sure you have a good solid clean ground strap to the frame, and the battery to the frame. Small problems here can cause weirdness


Here is what should be happening

With no br/ye at all connected to the alternator there should be zero volts at the alternator, maybe .3 is close enough to zero, don't know

with that wire completely disconnected from the alternator[as in both quick disconnects are free, no IG no L] you should have 12 volts on the wire whenever the ignition is on.

With the br/ye wire still disconnected, start the car and see if it charges when the revs are over ~2500. Some will, some won't doesn't mean anything by itself.

If you have 12 volts on the br/ye wire with the ignition on, plug it onto the IG terminal, the alternator should charge from high idle, but don't blip the throttle high. The purpose here is to see if connecting the wire makes a difference.


So, if the alternator, when just the IG wire connected charges, from high idle with out having to rev it to start charging, then we know the br/ye wire is supplying current to fire the regulator, not the alternator powering itself.

so, if for instance with on regulator connection, the alternator charges after you blip the throttle up to 2500 or so, and maintains that behavior with the wire connected, we can assume that the alternator is not getting any useful power through the wire for one reason or another, and search there

If it charges from high idle with the IG terminal connected as we expect, connect the L terminal. If it ceases to charge, it really has to be a defective regulator. Check the voltage up at that termination where the control box used to be,
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PostPost by: gjz30075 » Sun Mar 15, 2015 5:24 pm

My answers are in italics, in the 'quote'.

gus wrote:I am still not following exactly when voltages are happening where

One thing first, check the ground side connections. Make sure you have a good solid clean ground strap to the frame, and the battery to the frame. Small problems here can cause weirdness
Grounds are good


Here is what should be happening

With no br/ye at all connected to the alternator there should be zero volts at the alternator, maybe .3 is close enough to zero, don't know

with that wire completely disconnected from the alternator[as in both quick disconnects are free, no IG no L] you should have 12 volts on the wire whenever the ignition is on.
Yes

With the br/ye wire still disconnected, start the car and see if it charges when the revs are over ~2500. Some will, some won't doesn't mean anything by itself.
No, it doesn't

If you have 12 volts on the br/ye wire with the ignition on, plug it onto the IG terminal, the alternator should charge from high idle, but don't blip the throttle high. The purpose here is to see if connecting the wire makes a difference.
Yes, it charges when connected


So, if the alternator, when just the IG wire connected charges, from high idle with out having to rev it to start charging, then we know the br/ye wire is supplying current to fire the regulator, not the alternator powering itself.

so, if for instance with on regulator connection, the alternator charges after you blip the throttle up to 2500 or so, and maintains that behavior with the wire connected, we can assume that the alternator is not getting any useful power through the wire for one reason or another, and search there

If it charges from high idle with the IG terminal connected as we expect, connect the L terminal. If it ceases to charge, it really has to be a defective regulator. Check the voltage up at that termination where the control box used to be
Yes, it ceases to charge. I'll pull the alternator and have it checked.
,


Another quirk: All looked well, even after I connected to the L terminal. No ign light and it was charging
YEA! I shut it off, then turned the key to on, ignition light is on, and started the car. Ign light remained on
and alternator not charging. UGH!

I suspect the alternator will check out fine but I'll report back.
Thanks for hanging in here with me Gus.
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PostPost by: gjz30075 » Wed Mar 18, 2015 12:19 am

Alternator checks out good. Something in the light circuit is screwing this up, I'm sure. Time for some real
digging :-(.
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PostPost by: collins_dan » Wed Mar 18, 2015 1:16 pm

Maybe before all the digging, just run a temporary wire to the light, so that you can determine if it is the wire.
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PostPost by: gus » Fri Mar 20, 2015 11:54 am

I guess what Dan said. Perhaps run a whole new light 'circuit'

wire from switched power to a light bulb, from the bulb to the light terminal, see what happends
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