wiring issue

I just pick up a 1955 ford f-100 from a man who said he could never get it to run.After a couple of hours checking the fuel and spark i was able to get it to start and run.The issue i have is it will only run if you turn the ignition to start and hold it in the start position.Once you release the key to the run position it kills the engine.not sure if its a ignition switch problem or its wired wrong.



thanks for the help

 

If there is a ballast resistor, it would be bad, with what the symptoms are....or..

Turn the key to on, without it running. Then see if there is power at the key switch on the I terminal. If not, it would be the switch.

There are more tests you can do but start there. IMO

 

Ballast resistor, or in many older cars a resistor wire, between the ignition switch and coil +. When the starter is engaged a 'ballast bypass' supplies full battery voltage to the coil then when the key is released power is then supplied via the ballast resistor. The ballast is there to trim the voltage to ~ 10 volts, so that when you're cranking and battery voltage drops, the bypass is actually supplying ~10 volts (battery voltage under crank). The whole point is to have a 10 volt coil, which will supply best spark during start. Once running without a ballast the voltage would go too high and damage the coil. To test run a jump wire from battery pos to coil pos and see if it'll run. If so look for a white ceramic block with wires either end near the coil. If no ballast resistor it will probably have a resistor wire, just trace the wire from coil pos to the ign switch, checking every connector as you go until you find the open circuit. A test light is a must for this. Good luck!

 

It could be a bad ignition switch, or ballast resistor, it depends on how it is wired.
Is it original, or modified?
Sounds like an easy fix, good luck with your truck.
Hey throw us some Pics!

 

solenoid wiring backwards ... had this happen to me before, damnest thing.

 

Check the feed to the coil. It should be live in the "key on" position. It sounds like it is just live in the "key start" position. If this is the case trace the coil wire back to the ignition switch and change it on the terminals to the " key on" position.

A quick check would be a wire from the battery pos. terminal to the coil pos. terminal. Turn the key to "start" and release the truck should run until you take the wire off.

I hope that made sense.

 

Thanks for all good advice once this rain quits i will check all that out.

 

If it's 6v there won't be a resister.

 

I was gonna say...it's pretty hard to tell what's wrong with it because the symptoms are something that happens on 12v vehicles, and it was originally 6v. Without some pictures or description, we are just guessing at how it's wired.

 

Hi.. The main coil wire could be connected to solenoid terminal on ign switch....Doug

 

if its older wiring, it'll be a blown fusible link! gm used to run these
undersize wire so that if you had a voltage spike the fusable link would burn out saving the main wiring. finding it may be a bit of a pain though!

 

I just checked and I have power at both sides of the ballast.Then i ran a jumper wire from the batt to the coil and it stayed running.

 

now trace from the ballast to the coil. It's either cut, or maybe it's wired wrong.

 

Thanks for the info.I found that sombody had the wire from the ballast resistor going to the starter terminal on the solenoid.So i removed it and installed it to the + side of the coil and it runs like a champ.

 

Score. Nice when a plan comes together.

 

good news!

some more old iron back on the road... now let's see it.

 

You didn't say what motor you have but here is what usually does what you describe. There is usually a power source that feeds the coil when you are in the "start" position on the key. Then when you release the key to the "run" position there is another wire that goes from the "Ignition" post on the ignition switch to the coil.

The idea is, you get a full 12 volts while cranking then when the motor starts the coil only gets a reduced voltage through a resistor, or resistor wire coming from the "ignition" post on the switch to the + side of the coil.

What is happening to you is that the coil is getting that 12 volts during cranking, but when you release the key to the "run" position something is not connected from the switch to the coil. Either the wire is broken or not connected, the resistor is bad, or the car is wired wrong.



Don

 

Awsome! HAMB WINS! HAMB WINS! That wiring problem never knew what hit it!

 

The "S" terminal (start) is to provide a full 12 volts for starting purposes, then when key to "run" the ballast resister provides lower voltage (approx. 8 vdc) to allow running but reduced voltage to points and primary side of coil. If 12 volts to coil in run position the points will burn up prematurely.

 

I found that sombody had the wire from the ballast resistor going to the starter terminal on the solenoid.So i removed it and installed it to the + side of the coil.is that correct.

 

Not enough info


That old wire might have been correct, "if" the wire came off the I terminal on the solenoid, and then went to the coil side of the ballast resistor.

That would have been the full 12v "jumper" to the coil, only in the cranking position. Then, as you let go of the key and it went to the run position, you would then be running off of the resisted voltage.