resistance in ignition circuit?

[Beltfed]

I've been trouble shooting the electrical system on the 38 and found at first 10 ohms of resistance from the negitive battery post and the hot side of the ballast resistor pack. Found loose wires at the ignition switch which solved most of it. Still had 3-1/2 ohms resistance. Measured across the circuit breaker and there was the resistance. The question ...is that resistance normal for a unpowered circuit breaker? Knowing that the circuit breaker is a mechanical contact there will always be a certain amount of resistance at the contacts. Too much? Thanks.

Edited June 13, 2015 by Beltfed (see edit history)

[Beltfed]

I found the problem. The PO rewired the car and wired the ignition switch to the wrong side of the circuit breaker. The resistance I was reading was the circuit breaker coil resistance. After reading up on this so called circuit breaker I realized it's more like a vibrator than a circuit breaker. The current to the lights goes through the coil. I guess thermal circuit breakers had not yet been invented in 1938. Also the only wiring diagram I have is was drawn by a sixth grader, almost impossible to make out what wire goes where.

This car is like swimming in unknown water...one never knows what's going to reach out and bite your behind.

Edited June 13, 2015 by Beltfed (see edit history)

[abelincoln]

If your test meter is like mine, you'll find a couple ohms resistance in the leads.  Never gets to zero.

Abe

[Beltfed]

I use an analog Simpson 260 meter when working around cars. I own a number of electronic test instruments including several DVM's. I have worked in electronics since I went to work for Uncle Sam at 18. DVM's, with the numbers jumping around drives me nuts especially when whatever value I'm trying to read is not steady. Most if not all analog meters have a zero adjustment. Just short the leads and zero the meter. I do use a DVM if I'm looking to measure a small voltage precisely like voltage regulators.

[19tom40]

I have a wiring schematic for the 1938 Zephyr and can post it if you need it.

 

My understanding of the circuit breaker is that excess current heats the element opening the contact points and when the element cools the points close again to deliver voltage to the lights. This was done to ensure that you would have enough lights to pull safely over  to the side of the road. Thia was a big improvement over the head light fuse. I had a headlight fuse blow after going through a puddle on a moonless, cloudy night back in 1949. It was like driving with a bag over your head and I almost put the car in the ditch. Thermal CBs were in use in the 30s, but not in car headlight circuits for safety reasons.

 

I seldom take resistance measurements on cars any more, I prefer to do a voltage drop test. I also use my Weston analog meter to set the voltage for the regulator as I find it easier to to use for this purpose than the Fluke DVM.

[Beltfed]

19tom40, It doesn't work quite like you described. It's a current relay or vibrator. The relay contacts are normally closed. The current is passing through the coil, the closed contacts, then the lights. If a short or whatever occurs after the relay then the higher current than normal causes the contacts to open due to a stronger than normal electromagnetic force at the coil. As soon as they open they close, etc. This will cause a buzz that you will hear plus the lights will act strange.

The diagram I have is from the Ford Service Manual. If you have a good diagram please post. It will save me from having to draw one. Thanks.

[Guest Flyer1]

Interesting stuff, believe it  or not, some cars over here, 74ish used a heated "regulator" (basically a coil of of wire around a bimetalic strip that would "vibrate" according to current draw)  to run the instrument panel and gauges on the dash.

 

They also had a 'fail safe" set up in the light switch that would not completely leave us in the dark if something went wrong, it was sort of a "pinger" type set up where by it would on/off to keep the lights at least half going.

 

Analogue meter on automotive stuff , yes, DMM's can give a very false reading,they will read "stray" voltage and give a false reading.

 

As far as the resistance in an ignition circuit goes , the resistance wire (if it had one) was usually there to protect the coil under running conditions , it was usually "bypassed" (full battery volts to coil)  on start to allow for voltage drop when the starter kicked in to supply what was left of the voltage/current to the ignition system for a half decent spark at startup...if that makes any sense....

[19tom40]

Here is the wiring schematic, I hope that it is better than the one that you have. I have also attached the page describing the circuit breaker. This description is exactly the way that the circuit breaker in my car is wired and functions.

IMG_20150615_0001.pdf

IMG_20150615_0002.pdf

Edited June 15, 2015 by 19tom40 (see edit history)

[Beltfed]

19tom40, That description is interesting. I had to reread it several times to try and understand it. It is as you stated about how the thing works. The description I have said nothing about the bi-metal armature. What I don't understand are the following two descriptions.

"Therefore, an increase in amperage increases the magnetism in the coil which exerts a greater PULL on the armature.

And

However, the excessive current passing through the bi-metal armature causes it to heat as the tempature rises and the bi-metal expand unequally and causes the armature to PULL AWAY from the magnetic field.

I going to think on this and in the mean time will try to post the description I have.

Thanks for sharing both the diagram and operating description.

[19tom40]

I don't have a spare circuit breaker any more, I have sold the ones that I had, so I cannot disassemble one to refresh my memory of what the inside looks like.

 

Here is Ford's schematic drawing of the circuit breaker. It is located at the top center of the diagram.

 

http://www.vanpeltsales.com/FH_web/FH_images/FH_electrical-pics/Flathead_Electrical_wiring1940dlx.jpg

[Mssr. Bwatoe]

fairly simple, if the circut shorts,the shorted issues causes the  magnet to become powerful enough to open points that send power to headlights, 

causing a buzz and loss of lights..

[Beltfed]

Wow 19tom40, From the attached information we both are correct. I like that idea! On the left side of the page is the description of how my '38 works. On the right side is the description of the 1940 and up. It also clears up my understanding on how the 40 and up works. This is the kind of stuff that helps all of us better understand what Henry and his engineers were thinking by batting it around and understanding the small differences between model years. Thanks for your input.

I should have said I didn't read far enough into the circuit description instead of it saying nothing about the bi-metal in an above post.

Edited June 16, 2015 by Beltfed (see edit history)

[19tom40]

Beltfed, I don't know how I missed that in the Service Letters. Thanks for pointing it out. Now I understand how you could have one definition and I had another. The next page describes the change made in 1941, incorporating a dual circuit breaker in the box on the firewall, one for the lights and another for the accessories. There were further changes made for the 49 and later cars, but I don't have the information handy.

[dxod]

Beltfed and 19tom40, do you have the full first page and the next page for those of us with post 1941 cars? (Like my 48)

Thanks

Dan

[19tom40]

Here are the 2 pages on the subject

 

light circuit breaker.pdf

 

light circuit breaker 2.pdf

[dxod]

19tom40- thks

Dan