I have a 1985 F150 that I completely converted to Duraspark II ignition, using all factory Ford parts from a 1983 F150. My question is regarding the starter solenoid connections.

The Motorcraft starter solenoid I have only has THREE connection points, when most of the replacement ones I have seen have FOUR connection points. I am wondering if I am missing anything? This is how mine is wired:

- The positive battery cable is connected to one of the bigger connections
- The starter wire is connected to the other bigger connection
- The "start" wire is connected to the only small stud on the starter relay

Aside from a slow cranking problem when my engine is hot, my truck runs GREAT!
Why do the replacement solenoids and most of the others I have seen have a FOURTH connection?

 

I think some of the old trucks/cars had a fourth wire or the fourth hook up is used when the relays are in a different application. IE: that type of relay is found on wenches, tractors, and many other electrical set ups, so it is cheaper for the manufactures to make the one type,4 hook ups, than to make 2 that are almost alike. Mike

 

Well, that makes sense, except that my starter solenoid only has THREE connection points, and not FOUR, like most of the others I have seen. It is a MOTORCRAFT unit.

The others I have seen have two large connection points and the two small connection points are labeled "S" and "I". Mine only has ONE small connection point, and that is where my "Start" wire is attached to.

So I guess you are saying that I am not missing anything?

 

Since you converted your truck over, it would be a good idea to get a 4 terminal solenoid and hook it up. This 4th terminal (the "I") is used as a ignition resistor bypass. This puts a full 12v on the ignition coil during cranking, and makes the engine start quicker, especially in cold weather. With your duraspark II conversion, you should have added or verified that you have a resistor in the + feed to the coil.

Some of the later trucks(most likely the 83 you got this stuff from) got rid of the "I" terminal, and instead used a special extra contact located in the ignition switch, which did the same thing(bypassed the resistor in the start position). Most of the time though, it's easier when retro-fitting an ignition, to just add the 4 terminal solenoid, and run a wire from the "I" terminal to the coil + in the engine compartment.

There are some special 4 terminal solenoids, but like someone said you will only run across them in forklifts and equipment, and they will not be labeled "S" and "I". They usually are the ungrounded type, were to make the solenoid fire, you have to have ground on one small terminal and + on the other small terminal.

P.S. Do you have the white wire of the module hooked to the "S" wire going to the solenoid? That would help your hot starting problem.

 

Thanks Franklin. When I converted over, I found that the factory resistor wire was already in my harness, even though my truck originally came with TFI/EEC-IV ignition. This was a simple plug and play; all I needed to do was unhook my existing ignition/computer mess and plug in the duraspark harness to my existing plugs. Everything seems to work fine, including my tachometer, except hot starts can be very slow sometimes.

OK, I did get all the components from a 1983 F150 with the same engine. So I guess that means I am using the special contact located in the ignition switch??

How would I find out for sure if I need that wire that goes from the solenoid to the coil + or if my truck is using the special contact in the ignition switch?

I hooked this all up EXACTLY the way it was on the 1983 model. There was only ONE connection that went to the "S" solenoid that I could see, and that was a single wire that came from the firewall. This is the same wire that was in the same location on both the '83 and my '85. Same color and everything.

How can I check to see if the white wire of the module is indeed hooked to the "S" wire going to the solenoid?

Thanks for all of your help!

 

To check and see if the resistor bypass is working, hook a meter to the coil + and ground the other lead to the engine. Crank the engine while watching the meter. The voltage should be high during cranking, and drop a little bit after it gets running. The difference may only be slight, depending on the strength of your battery, since the starter will pull the voltage in the truck down a little bit while cranking.

To check the spark retard function during cranking, take the meter and stick the white wire going to the module and put the other lead to ground. You should have 12v on this wire during cranking only.

 

My 1981 does not use the I terminal either. It's wired in the harness, as on the 1983 you guys are mentioning.

Factory installed Solenoids were three connection, like you have now, "Lariat".

Replacements have four, due to the 70's era trucks need them, and it's silly making and stocking two solenoids that are almost identical, like was stated above.

Nothing is missing from your truck, "Lariat".

 

IMPORTANT:

Also be aware that the color of the start and run wires on the truck, and the start and run wires on replacement modules have been reversed.

The white start wire on replacement modules hooks to the Red/Blue stripe wire on the truck harness side.
The Red run wire on the replacement modules, hooks to the White wire on the truck harness side.

Here is a picture of the Power Plug for the module. See how the wires change colors through the plug from one end to the other? This is normal on replacement modules.

 

Thanks Franklin. I will try that voltage test on my module wires this weekend.

81-F-150-Explorer, you are correct on the module wire reversal on the replacement modules. I am running a replacement (non-Motorcraft) module I got from a junkyard, and the wires are indeed reversed.

When I got the wire harness from the '83, I also grabbed the module, and it had "MOTORCRAFT" embossed in it with the "Duraspark" identification. I notice the original Motorcraft unit is much thicker than the replacement module, and the red and white wires are correct to the plug on my truck.

Why are the wires reversed on the replacement module, and does that make it different somehow? Like maybe the "spark retard' function may not work with the thinner replacement ignition module?

Hmmmm....

 

I have heard rumors on here of that being a possibility, but have not verified if it's true. Maybe you can see if there is some truth to this. The engine should turn over noticeably easier if you are trying to start it about 5 minutes after turning it off on a hot day, with the spark retard.

Several of the aftermarket racing ignitions have this feature since high compression engines are so hard to turn over. I worked with a guy who actually just put a switch on the coil wire. He got the engine turning with the ignition off to gain some momentum, and then flipped the switch to fire it.

GM's are famous for the weights in the dist getting rusty and sticking in the advanced position. I had a car do this once it awhile if I didn't keep wd40 on them, and if it happened to me while I was out, I found if I flooded the engine by pumping the gas a couple of times, it would turn over easier till it cleared out and then it would start.

When you have this problem, instead of the engine turning smoothly with the starter, it will go "rump" "rump" "rump" each time one of the cylinders fires. And this problem will totally go away on a cold morning start.

 

I have seen replacement "Motorcraft" modules also with the wire color reversal, but the factory originals were the same color all the way to the module.

I have also heard the same rumor as Franklin, but again have never verified it.

And the following is also confusing, but correct....

Factory diagrams state, Red/blue stripe is start, White is run. Which is the correct colors for the truck.

Aftermarket diagrams state, White is start, Red is run, Which is also correct for replacement modules.

Which would make sense to why the colors change at the plug.

Who knows if the replacement modules are wired correctly or not?

Probably more of a reason than ever to buy a motorcraft one, even if it does cost more.

 

*****UPDATE*****

Well, I FINALLY found my "hot start" problem. The engine would start fine when cold, but would drag really slow when hot. It finally would not crank at all today after it got hot.

The problem was a GROUND WIRE! The ground from the battery to the engine block was severly corroded, rusted, and loose. Took everything off, cleaned and sanded the surfaces, replaced a washer, and the problem is SOLVED! I thought my truck started fine before, but not compared to how fast it starts now! The engine barely has to crank at all, just fires right up with a bump of the ignition.

CHECK YOUR GROUND WIRE!