Resistance unit

[bobv]

What does the "Resistance Unit" in the wire from the ignition do?

[Joe KCMO]

I assuming you have a 6 volt ford. The resistor lowers the 6 volts to about 2volts for the points in the distributor. I am not exactly sure of the voltage, but you get the idea.

[G.M.]

Joe it lowers the coil voltage to between 3 1/2 and 4 or slightly higher volts. At 2 volts the coil will not put out a strong enough arc to stay lite across the spark plug gap when the compression comes, it will blow the weak spark out. Below 3 volts it is hard to start and will sometimes start just as you release the stater button. The voltage raises when the starter load is gone, the engine is still spinning and a stronger spark fires the engine. Some plugs will get like this and when tested properly in a plug tester air is put into the "ignition chamber" of the tester and as the air pressure is increased you can see through a sight glass the spark blows out as the "wind" gets to say 35 pounds. On good plug you can go to a 100 pounds or more and the is little or no change in the spark. G.M.

[bobv]

Yes 6v ford 85hp. I just got the car and trying to get spark, it has been sitting for 60 years. I'm working my way thru things and found the resistor and thought maybe it's bad. I haven't done distributor yet, the parts are on the way. Thanks for the info, i'm sure I will have plenty of questions as I have never worked on one of these before, learning as I go.
Bob

[G.M.]

When they sit for years the points get a corriosive coating on them. You need to clean the points, check the voltage to the coil. The voltage should be over 6 volts with the points open and close to 4 volts with them closed. You can tell if the points are working by just bumping the starter and you can tell by the voltage if they open and close. If they don't work it won't run. When they work have someone crank the engine and while the engine is turning squirt a good shot of starting fluid down the carb. and several small squirts to keep it running. Starter fluid will start it when gas won't. Start out with a fully charged battery so you get full voltage to the coil. G.M.

[bobv]

Sponsored Links (Register now to hide all advertisements)

Still no spark. The only way I can get spark is to jump direct from battery to coil. I have checked voltage from battery to Ignition switch, to resister, to coil without the jumper wire and all seem fine around 6.48v, and I get 2.55 to 2.75 from coil wire to ground. What am I missing?
Bob

[Bill OH]

Remove the 2 screws holding the ignition switch terminal block to the steering post and clean the contacts inside the switch. Also remove the Bat and Ign wires and clean the eye terminals with either a flat file or sand paper and also so the same to the terminal nuts. Remove the 4 nuts from the resistor block, run the nuts across either sand paper or flat file and do the same to the resister terminals and the 2 ring terminal wires, remove the resistor and silver bearing solder the nichrome wire ends to the terminals and test for continuity with an ohmmeter. Reassemble putting on two nuts, one on each post, followed by the resistor terminals, then the wire ring terminals, and lastly the nuts on each post. The connections that I have described cause problems that are not solved with points and plugs. Connections need to be CLEAN AND TIGHT.

[Mr 42]

The resistance unit provides the right voltage under driving conditions.
The coils are designed to work at 3.5-4.5 volts leaving maximum spark

When you start the engine the starter will draw current and lower the aviable battery voltage to around 4 volt.
When the resistor coil is cold it will passthru all the voltage, providing around 4 volt to the coil, and it provide maximum spark.

When the resitor heats up by the current drawn thru it. it will lower the now incomming 6-7 volt from the battery to around 4 volt. And not causing the coil to overheat.
Thats what the resistor do.

[Joe AZ]

I had original wiring in a '40 coupe I bought, and had intermittent spark. Turns out there was a broken wire in the original wiring harness between the resistor and coil. If you've got original wiring, might be a place to look.
Joe

[bobv]

I will go thru the connections again, I think that is my problem just can't find it. I did replace the resistor to coil wire. There are not many wires but it is sure giving me a bad time. Anxious to get it running, it been sitting since 1951.

[G.M.]

Sounds like a dirty, wornout ignition switch. check the voltage that comes into the switch and out to the resistor UNDER LOAD. G.M.

[Mr 42]

If you connect a wire from the battery negative post to the ignition coil.
you should be able to start the engine and run for a couple of minutes, without problem.

If it works the problem is between the battery and the coil, otherwise you have a problem with the coil or distributor.

[bobv]

Now we are getting somewhere. Started at the battery cleaning and checking wires and when I took the ignition switch apart it was dirty with some wear. I bypassed the switch and she started. Only ran for a couple of seconds then died but that's Ok for now battery was getting down anyway. So I will get a new switch, charge the battery and try it again in a few days. I do think it's fixed. Thanks for the help, I will post again in a few days with progress report.

[G.M.]

You can fix the switch better than it was when new. The rounded ends of the ball contacts don't make much contact area on the brass pads. The black phonolic and the pads were machined with a large cutter that put ridges and groves on the surface. With the small ball on the end of the contacts they are sitting on the ridges makeing very little contact and arcing occures. Put 320 sand paper on a flat surface and sand the phonolic and brass pads to a smooth surface, sand it again with 1,000 so it's smooth. Take a small screw driver and bend the balls down maybe 1/32" being careful the spring don't pop out. Put the 1,000 paper on the flat surface holding the assembly straight and sand the balls all at the same time until you get a flat about 1/8" or less on the ends. Now when installed you should never have a switch problem again. G.M.

[ssrcobra]

I found this old post that I would like to add on to with a question.

If you turn on the ignition and don't crank the engine will the resistance unit overheat? If not what would cause it to over heat? A short? I've traced the wiring 5 times and everything seems correct

Thoughts?

[JSeery]

If you leave the ignition switch on and the points happen to be closed you will overheat the coil in a few minutes. Not sure about the resistance unit, but it would have current flowing through it which would heat it up. This is a good way to destroy a coil by the way.

[V8COOPMAN]

Originally Posted by ssrcobra

I found this old post that I would like to add on to with a question.

If you turn on the ignition and don't crank the engine will the resistance unit overheat? If not what would cause it to over heat? A short? I've traced the wiring 5 times and everything seems correct

Thoughts?

Given your above scenario, it will overheat if the points happen to be closed at the time. If the engine stopped with the points in the open position, no current will flow and the resistor will not heat-up. DD