Right. I am trying to bring back to life a 1948 desoto suburban that has been sitting underneath a tree for quite a long time. When I cranked the engine it turned freely but It wont run. I checked for spark and got nothing. I installed a good, full charged 6v battery, turned the key on and checked if I had power to the coil, I found with a voltmeter that indeed I had a bit less than 6 volts to the negative side of the ignition coil, my next step was to check the ignition coil itself, I tried to bypass the circuit to the points/condenser using a wire from the negative side of the coil, plugging a spark plug directly to the ignition coil main wire that goes to the distributor, grounded the spark plug to the engine case and did several quick shortcuts to the engine coil to see if the sparkplug would fire but nothing, then I removed the ignition coil and checked primary and secondary circuits and I got very low numbers in the voltmeter so I thought the ignition coil was the one to blame. So taking advantage of my trip to the auto part store I decided to get a new set of points and a condenser too. I installed all of them into the car, I did set up the point gap to the specifications corresponding to my car (0.020) and I checked for spark again. I was sure this time I would get spark from the main wire coming from the coil but still nothing. As many of you guys sure know, the car is positive grounded, I dont know if I am doing something wrong since this is the first time that I've had to work with the electrical system in a positive grounded car. Any suggestions?
Sounds like youv'e done everything right, I would suspect the coil. If you can't get your hands on a 6 volt coil, isolate the ignition system from the rest of the car and substitute a 12 volt coil and battery. You can just power up the negative side of the coil and earth a plug coming from the centre post of the coil, as you already have.
Hey! Thanls for your comment brother. I actually replaced the ignition coil with a brand new 6 volt one, I threw in a new set of points and condenser but didn't make the trick. I can't think in nothing else to do to make it work. Maybe something is not properly grounded, I'm kind of lost here.
Pos ground makes no difference, works the same as any points ignition system. I would be checking step by step. Is power getting to the coil? Is it getting from the coil to the points? Are the points making and breaking the circuit? You can check this with a 6V test light or a multimeter. If this is all correct you should get a spark from the coil, you can check by sticking a plug wire into the coil and setting the plug on the head and see if it sparks. You can do this by flicking the points open with a non metalic stick. At this stage you should either have a spark or know the reason why. Check for frayed or broken wires, grounded wires, your car may have the self shifter transmission which has controls that work off the coil, you can temporarily disconnect these wires until you get it running. Just to eliminate one possible problem. Once you are getting a good spark you can clean and inspect the cap and rotor put it together and see if the plugs are firing. One more thing is to check the timing and make sure the plug wires are all going to the right plug, for some reason they get mixed up especially # 3 and 4.
What he said - you should be able to "open" up the points from a closed position - and get a spark there - open with a screw driver....if it does spark - keep the distributor off and make sure the rotor is turning as yoou crank it... if you have spark there - look at the rotor or cap.....
Should get spark with key on - if not we should look at a hot wire to the coil from the battery.......
With the key on and the points closed, does the distributor side of the coil go to zero volts? If it doesn't, and I think that may be the case, you don't have a ground at your distributor.
I want to thank each of you for your comments trying to help me out. I finally got a spark. There were a couple of issues,. Since the beginning, as I mentioned in my first post, I had close to 6 volts to the negative side of the ignition coil with the ignition switch on, but that was it, there was no power beyond that point. It turns out that a little wire coming out from the base of the points got no insulation at all and it was touching permanently the distribuitor body, so I taped that down properly and that was that. Then I came accros a second issue, my desoto has a kick off relay that governs the transmission; following the wirimg diagram, one of the wires coming out from this relay goes into the positive side of the ignition coil, the problem is that if I hook up that wire, I don't only lose spark from the coil to the distributor, but I got some smoke coming from the wires in the negative side of the ignition coil. If I leave it unplugged, I got a perfect spark all the way to each sparkplug. I cleaned perfectly well each of the 5 terminals on the relay and I repaired every piece of non-insulated wire but I still got the same issue each time I try to hook up that freaking wire to the positive side of the ignition coil. I suspect I got a short and probably comes from inside the relay. Should I try to pry off the cap of that relay and see if some oxidation in the points inside is causing the problem? The desoto manual mentions I should not do it and that once this relay is faulty it must be replaced, but I've seen some comments about other similar relays were some people had those opened and cleaned. Any words of wisdom?
Pry off the cover and see if the points are stuck closed. Use some fine sandpaper or emory paper on the points and try it again. What have you got to loose?
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