40 Ford Ignition Woes

[Lawson Cox]

Originally Posted by Ken/Alabama

Check the ignition switch at the steering column. Take it off and check the contacts. They get corroded and burned and cause a high resistance.

Good call Ken.

[Juergen]

You can eliminate the cap/rotor by checking the output of the coil. No spark there (along with no spark at a plug) says it is not a cap/rotor problem.

You have 6.2 volts at the coil. What do you have at the points side. Steady 0 would imply that the points stay closed, while 6.2 volts would imply that the points remain open. Assuming you have an analog meter, a slow crank speed should show some needle movement that the points are opening and closing.

[philipswanson]

Originally Posted by Ken/Alabama

Check the ignition switch at the steering column. Take it off and check the contacts. They get corroded and burned and cause a high resistance.

I put a jumper between the neg battery post and the neg side of coil. Still no spark. It's frustrating because the system is so simple. I am looking to the cap and rotor next.

[philipswanson]

Originally Posted by Juergen

You can eliminate the cap/rotor by checking the output of the coil. No spark there (along with no spark at a plug) says it is not a cap/rotor problem.

You have 6.2 volts at the coil. What do you have at the points side. Steady 0 would imply that the points stay closed, while 6.2 volts would imply that the points remain open. Assuming you have an analog meter, a slow crank speed should show some needle movement that the points are opening and closing.

I'll check that next with my old Simpson analog meter. Thanks. Points are new and set up on a Sun machine but still could be the problem.

[Mart]

Cap, rotor or wires.
These have caused me trouble before.
I mentioned it in post #2.

I replied having only read page 1.

If you have pos ground and touch a neg jumper to the neg side of the coil it probably won't generate a spark.

You need to have a constant neg feed to the coil and intermittently connect between the pos terminal on the coil and ground. It should generate a spark as you remove the contact with the ground.

[philipswanson]

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Where is the best place to buy a new cap and rotor for the 47 crab? I think that is the problem.

[torpedo]

Thirdgen auto is the go to place. Michael is very helpful.

[Mart]

be careful. The "crab" cap with the wires exiting sideways is (something like) 41-42. A 47 cap would be the rabbits ears type cap. The rotor arm is specific to each type.

[philipswanson]

Originally Posted by Mart

be careful. The "crab" cap with the wires exiting sideways is (something like) 41-42. A 47 cap would be the rabbits ears type cap. The rotor arm is specific to each type.

Does this mean either type is ok for the 47 crab as long as you run the right rotor for a given cap?

[Mart]

Well, what I was really getting at is what type of cap do you currently have? If a crab type, you need the crab type again. If a rabbit ears type, you might want one of those, but might want to go to a crab type for simplicity.
The term "47 crab" in not strictly correct. In 47 the distributor was the same as the earlier ones (true crab type) but was modified to take a new cap, which is nicknamed the rabbit ears type cap.
From an ease of fitment point of view, the earlier crab cap is the popular choice.
Mart.

[35fordtn]

The 47-48 has a two piece cap… a real pita to work on. The 42-46 has the crab type cap that many prefer. The only difference is the cap, rotor, and retaining clips. We offer all three items all made in the USA

[pistonbroke]

I'm no know it all but what I'm seeing and hearing here is a loose or corroded connection heating up and losing continuity. I would start at the battery and work my way to the points cleaning and checking resistance at each and every connection. I had a little experience with this when I bought my 41 pickup. It took me awhile but I found it. Tim

[SoCalCoupe]

Originally Posted by Ken/Alabama

Check the ignition switch at the steering column. Take it off and check the contacts. They get corroded and burned and cause a high resistance.

OK. Unscrewed the switch from the lock. How do you check the contacts? Looks like you have to open the case. How do you do that without destroying the switch? This is a 1941. Don't know if that makes any difference.

[Ken/Alabama]

Originally Posted by SoCalCoupe

OK. Unscrewed the switch from the lock. How do you check the contacts? Looks like you have to open the case. How do you do that without destroying the switch? This is a 1941. Don't know if that makes any

That switch is different from the 40. I’ve never taken one of those apart. Maybe someone here has done it .

[1942deluxe]

Do the mounting holes go side to side or top to bottom?
I have NOS of both types. I could mail you one to see if
it makes any difference.

[SoCalCoupe]

Originally Posted by 1942deluxe

Do the mounting holes go side to side or top to bottom?
I have NOS of both types. I could mail you one to see if
it makes any difference.

Thank you for the offer. That is very kind. I will keep it in mind as I try to crack this nut open.

[Terry,OH]

confusing post since there are two people asking for assistance.

[Ggmac]

I’ve taken the 41 switch apart. Not hard . Drill rivets , be careful the spring inside is small plus a 3 sided contact plate. Clean both contact surfaces and I use super glue to temporarily hold the pieces together while I use small screws or rivets to reassemble.
Before you go through all that , you should check resistance through the switch at each of the 3 connections .
Another issue may be how many amps you have going through the switch at each. It wasn’t meant for much

[Veeder]

Another vote here on the ignition switch. Mine would heat up and the game was over. Bypass the ignition switch completely and see what happens

[Doublepumper]

The contacts in the switch aren't robust enough for much amperage draw. A good fix (in my opinion) is to install a relay to power everything up through the switch. Going this route, removes the load on the contacts. The switch now only activates the low amperage relay coil.