jd 40c won't start

[01hunter570]

I have a jd 40c that was running when I bought it, now can't get it running. i'm not sure which position the ignition switch should be in. I thought it was the first click to the right but not sure. I put in new points and condenser with no change, still won't start. I put the switch where I thought should be on and checked for power at the + side of coil with a test light but i'm not sure if I did it right as it is positive ground. I hooked the test lead to the frame and touched the probe to the + side of coil, no light. now i'm thinking the switch must be bad. does this sound right? how much trouble do they have with these switches as I also have an mc that basically acts the same. thanks in advance for any advice. 01hunter570

 

[Roadworthy]

The tractor may be positive ground but the test light doesn't care. It's a light bulb. If the clip has a good ground touching the probe to a source of power will get a light. Want to check? Ground the clip and touch the probe to your battery. It should light. If it doesn't light there it won't light anywhere else. Power goes from the battery to the ignition switch. If you turn it on it should go to one side of the coil. When the points close they ground the other side of the coil creating a spark. The condenser absorbs most of the spark at the points so they don't burn up and pit so quickly. If you replaced the points you have to set the gap so they open and close the correct amount. You should also put a little grease on the fiber thing that rides on the lobes in the distributor.

 

[01hunter570]

thanks for the reply Roadworthy. I gapped the points replaced condenser, replaced the spark plugs which I also gapped. all the old cars I worked on in my younger days were negative ground and I can't understand the principal of positive ground. is the polarity reversed on the battery so the negative terminal of the battery is actually where the positive energy exits the battery? if I ground the test light to the frame should I touch it to thee negative battery terminal to get it to light? where does the power to the ign. switch come from, the starter? thanks for your time and info, 01hunter570

 

[Roadworthy]

Many automobiles of the past have been positive ground. My 1960 Austin Healey was positive ground as is my 1972 Triumph motorcycle. Ford automobiles were positive ground into the fifties. Negative ground is the way it's currently done - the standard. As far as I know all current production vehicles (and tractors) are negative ground. I don't really know a valid reason for one over the other, I think it's arbitrary. Why have a ground at all? It saves a BUNCH of wire!! The only time you need to concern yourself with whether it's a positive or negative ground is when you replace the battery. Any battery will work. The battery doesn't care which side you ground, but if you ground the wrong side your starter may spin backward or something like that. When working on the tractor just figure ground is ground and the wiring is hot. Light bulbs don't care - though LED bulbs do. Your ignition system will work either way. I didn't ask whether your tractor was six or twelve volt. That was another change which came about in the fifties. There was a reason for that change. A twelve volt system requires less current to deliver the same power. That allowed manufacturers to use smaller wire, saving money in the process and increasing profits. The new twelve volt accessories worked better than their six volt brethren so that change was a win - win.

 

[DJ54]

The wire coming from the switch should be connected to the negative side of the coil. Check for power on that side of the coil, with switch on, grounding to frame, or positive side of the battery. If the test light doesn't light, in what you think is the "on" position, find the input lead to the switch, and check for power there. If it lights, go to the power out side, and check all positions on the switch. If it doesn't light, it's the switch. If you have enough room, you could probably run a jumper wire with alligator clips to the input side, connecting to the output side going to the coil, then check the negative side of the coil for power, grounding to the frame. If the test light lights, you definitely know it's the switch.

The only time the test light will light, putting it on the positive side of the coil, grounding to frame, or positive post on the battery, is when the points make contact when turning the engine over.

 

[1010]

Sometimes carbon will form on the points, button and cap. Especially if the switch was left on for some time.

EDIT, I see you added new points.

 

[01hunter570]

thank you DJ54, you gave me the exact info I needed.i'm leaning toward the switch. I checked the neg. side of coil with the switch in all positions and had nothing. I had a good grnd. on the test light because it lit when I touched it to the starter lug. i'm going to pull the switch and check it as you suggested. I checked and they have new switches on yesterdays tractor. thanks again for all the replys from the knowledgeable people on this site, sincerely 01hunter570

 

[DJ54]

If you haven't taken it out yet, you may try ratcheting it back and forth 15-20 times, then check to see if you have current flowing though it. If it has set out side, moisture may have gotten in it, and corroded the contacts. If you have it out, you can do the same, and a shot of something like WD-40 around the switch shaft may creep in and help clean things up. I've had it work less times, that I've had being successful, but you never know.

 

[01hunter570]

good idea DJ54 , I think i'll try that. maybe a little wd 40 first and follow up with some electrical contact cleaner I have. nothing lost nothing gained, if it doesn't work. thanks again 01hunter570.