QuestionQUESTION: Hello, I have a bad silenoid on my 78 spitfire I went to auto zone and they gave me a ford silenoid for use in replacement. It has the 2 large post on the left and right sides and the two small posts on top marked I and S. I was told to cut the ignition coil wire and run it directly to the coil. That means not hooking it to the silenoid at all. I can't get the car to even crank that wasy. I have hooked it up the way you had told another and identifiede the trigger wires. I can get the car to crank and even startt but as soon as I let go of the key the car dies. What am I doing wrong? Which side of the new silenoid do the positive and negative leads goto on the silenoid? Thank you
ANSWER: Hi Gregrory,
If you had a coil wire (white w/yellow tracer) and a plain white wire from a power resistor going to your original solenoid it was a resistor bypass system meaning you have a low volt coil. Here is how the system operated. With the key in "Ign" position power goes to a resistor or resistor wire and on to the low volt coil. When you turn to "Start" position the power to the coil is then routed direct to the coil as a full 12v. The solenoid supplies that power only when the solenoid is active. The reason it is done this way is because a starter motor uses so much current that the voltage drops so there is not enough for a coil to operate so they use a low voltage coil. If they just wire it direct it would over heat after the engine started and was operating at 12v to 14v. So a resistor or resistor wire is used to drop the voltage to the low volt coil. This is how the original Spitfire was wired but many have been altered over the years.
When they gave you a two small lead and two large lead solenoid it was designed to be used with a bypass system like your car had originally.
First test the solenoid by connecting up a ground to the base of the solenoid and a hot wire to the large hot post. Most likely the small posts labeled "I" and "S" are for "Ignition" and "Start" but to be sure do this. Take a small jumper wire and attach one end to the big hot post and with the other end scratch across the "I" terminal. You should see nothing. Then touch the "S" terminal with the jumper and it should activate the solenoid.
If this test was correct then connect your White wire and the White w/yellow tracer wires to the "I" terminal and the White w/red tracer wire and the white w/orange tracer wires to the "S" terminal. All of the plain brown wires connect to the large battery terminal on the solenoid and only the starter wire it self goes to the large starter lug on the solenoid.
Howard
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QUESTION: Howard,
Thank you for your rapid response. I did exactly like you said. when I touched the jumper wire to the "I" =nothing. When i touched it to the"s" the cars cranks. I placed the white and white/yellow wires on the small "I" post and the White/red and white/orange on the "s" post. When I turn the key the ign position i do not get a radio or any instruments. But when I turn the key to start I get a radio and dash components. Additionally, when i turn the key to start the car i can hear the fuel pump running. However, the car does not crank at all. I have changed the large positive and negative leads around on the large posts and still nothing. I cannot remember the sequence of where I had the wires but I had gotten the car to crank and run while holding the key in the start position. But as soon as i let the key ride back into the ign position the car dies. I can even hold a jumper wire from the pos terminal on the battery to the small "s" post and the car will run with the key riding forward in the start position. I am lost for ideas. Is it possible this is a non compatible silenoid? or have i just missed something?
AnswerThere is one more check of the solenoid that you must do to see if you have identified the correct Battery and starter post on the solenoid.
Check for a connection between the "I" terminal and each large terminal. One will have a connection and the other will not. Which ever has the connection, that is the "Starter" terminal and the one with no connection is the "Battery" terminal. The "Battery" terminal also gets all of the brown wires.
If that is how it is now, then you have a wiring problem. Probably at the ignition switch.
You need a wiring diagram laying in front of you EVERY time you try to work on electrics. If the wiring of the solenoid was correct as I out-lined then pick a SINGLE circuit of ONE item that don't work when you turn the key to "Ignition" and take a test light and go to that ONE item (called the Load) and test for power. If you find no power, use the diagram to locate the next joint headed toward the source (battery). With this method it is impossible to NOT find the problem. It is a 100% sure method of diagnosis. Over 90% of the time using this method of diagnosis, when there are several items that don't work, you will correct all of them. I found that it is best to pick a simple circuit to do this test. Follow each on the diagram to see which is the simplest circuit and use that one.
It is a waste of time trying to figure out what might be wrong by symptoms. Testing is the ONLY sure method to correct the problem. If you don't have a diagram, let me know and I will post one on my web site for you to copy.
Howard
