Farmall Cub

I should appreciate some help here. My two red tractors are a 49 M and 49 Cub. Recently converted the M to 12V - no problems. Works fine. Didn't wire the lights. Now converting the Cub - finished - but before re-installing the hood/tank, I see a problem. With light switch and ignition both off, when I connect the battery I get a 5 discharge on the ammeter (which is new 30-0-30). More observations: With lights off and ignition off, battery connected, I measure 12V at "L" terminal on alternator, 12V at Bat terminal on alternator, zero volts at resistor input and 12V at starter post. With ignition on, lights off, the ammeter moves to 7 discharge and engaging the starter moves it back to about 5 or 6 discharge, while the resistor has 12v in and about 8.5v out. New battery voltage at this point is 12.09 (not fully charged). With ignition off, lights on, I measure at the headlamp terminals 11.5V on "D" and 12.02V on "B" light selections. This all appears normal to me except for the ammeter movements. The wiring harness is relatively new, in good condition. The light switch is 4-pole original with 0, D and B indicators, but there is an unmarked stop between O and D, perhaps missing from the decal. No headlamp voltage found from that position. I suppose it is for a rear light, which this Cub doesn't have. Here is my sketch of the wiring, which I hope comes through, as I haven't done this before:


I bypassed the light switch, but the ammeter readings were the same. Checked the new ammeter for short and found none. I have 12v bulbs for the lights when re-installed. My electrical skills are elementary and I could use some tips about what to do next with the wiring or testing for faults. Many thanks.

Re message just posted, I see that the attachment cannot be accessed. Can someone tell me how to get it into a message?

burntgate wrote:Re message just posted, I see that the attachment cannot be accessed. Can someone tell me how to get it into a message?

Works for me.

Don M: When I click on the attachment all I get is the file reference. Is the diagram showing up for you, and how can I see it?

Click on the link. Select "Save". Then select "Open".

Burntgate,
move the wire that comes from the "L"terminal on the alternator to the other side of the ignition switch. And in this wire, solder in a diode with the cathode (the band) toward the alternator. And I highly recommend putting a 30-40 Amp fuse in the wire from the alternator "B" terminal.
Gerry

Here is a diagram of what Gerry is talking about.

Thanks, Don, for the attachment advice, and Gerry, John for the wiring directions. I had just left the "L" wire on that side of the ignition switch because it was already there. I'll make the changes Friday or Saturday and post the results. I can see how it will make a difference.
Glenn

The L wire from the regulator and the L ( or 1, depending on markings) of the alternator serve different functions. On the regulator it is how the ignition and lights get power from the battery. You can move the L lead to the bat. term of the alternator to provide power for the ignition and lights. The L (1) of the alternator is an exciter circuit to start it charging, hence the connection to the switched side of the ignition switch. If you do not install the warning light (not charging idiot light) or the diode, it will keep powering the ignition when the switch is turned off.

To simplify the wiring for battery ignition Cubs, consider connecting the alternator terminal shown as 1 on the #5 diagram above to the input terminal on the coil (shown as + on #5 diagram) instead of at the ignition switch. Just one short wire with two terminals plus the feedback-limiter device of your choice ( resistor, diode, lamp). No need to work at the ignition switch nor add a conductor to the wiring harness. The coil and alternator are in close proximity. For external coil resistors, the relative value of that resistance is so low that it makes no difference for alternator exciting on which side of that resistor the connection is made. This suggestion is functionally faithful to the schematic shown.
Opinions may differ.
For the feedback-limiter, and fuse if you choose to have one, they need to be mounted solidly to limit the movement from vibration. At the moment, I have no photos showing how I mounted the resistor on the back of the alternator to accomplish this. IH used a resistor on the Cubs with alternators and that is my preference also.

ibrake4rust wrote:And I highly recommend putting a 30-40 Amp fuse in the wire from the alternator "B" terminal.
Gerry

Of course bear in mind, it may still be "hot" on both sides of the fuse if it blows,depending on circumstance....It feeds from the alternator and the battery...Sounds like a mouse trap to me...Hey opinions are like , everybody's got one...

So true, some are just bigger than others.
If blown, the battery side is hot always, the alternator side is hot if the tractor is running but in either case there is not current flow. I've never heard of a fuse being referred to a a mouse trap. A fuse is a safety device used to protect electrical circuits.

A little history from the car side, applies to tractors as well:
Before about 1980, there were no fusible links on alternators, but after that it is common practice to have a fusible link between the alternator and battery to prevent fires and wire burning up in the unlikely event that someone installs a battery with the polarity reversed or if a diode in the alternator fails.
Another bit of info on alternators:
Alternators are NOT designed to be battery chargers! They have no regulation for current flow and will pump out current up to their rated output into a battery that will take it.

This diagram is from Alternator 101
Note the fuse, common practice. This diagram is for Delco 10 series but fusing equally applies to all brands used.

ibrake4rust wrote: I've never heard of a fuse being referred to a a mouse trap. A fuse is a safety device used to protect electrical circuits.

A fuse is only protection when used properly...If a fuse blows and creates the assumption the line is dead and you're the mouse, you may fry, well in this case, you might just get a flash,unless you've built up some gas fumes...Fuses blow for odd reasons, sometimes for no reason...And if assuming you're changing said fuse, you should be aware it may be hot on both ends as you have created a back feed to and from the fuse with the tractor running, the key word being " may be" as in be Aware of...I would rather have a battery disconnect switch while the tractor is sitting idle unattended, than a fuse that may cause more problems than necessary...Did I mention "Opinion"....I may have spent 35 years as a Power Company Hot Stick Lineman for nothing I guess...In that spectrum, fuses can kill you...No text book jargon please...Dave

Linemen get killed all the time working on high voltage transmission lines. But you'll never get killed changing a fuse on a tractor unless it runs over you.
Gerry

Gerry what purpose does the fuse serve? The more connections the more problems. Keep it simple in my opinion.