XR4Ti Archived Tech Articles

    3 Dollar Code Scanner - Who needs to spend $40 on an EEC-IV Code Scanner from an autoparts store when you can build your own for $3.


Post Date:    Sun, 29 Mar 1998
Subject:      How to build a $3 code scanner for your Merkur
List:         IMON


Note:  The following information is not the actual post made in March of 
1998.  That post contained very little information on how to build the code 
scanner, but rather pointed the reader to a web page with diagrams and 
explainations describing how to do the job.  What you are about to read is an 
updated version of the web page posted in 1998.



Click any of the thumbnails below to see the fullsize image.


parts and tools Parts and Tools. These are the tools I used to complete the job. I used; wire strippers, wire cutters, an "experiment box" from Radio Shack, an eyeball maplight from an XR4Ti, a 12 foot roll of wiring (with a couple feet leftover), an alligator clip, 3 male quick-disconnect spade connectors, and 2 butt connectors.




wiring assembly detail Wiring Assembly Detail. This image shows the detail of the area that plugs into the EEC-IV STO/STI plugs in the wiring harness. Note that, even though I hadn't done it yet, the male spade connectors I used had to be trimmed slightly to fit properly into the plugs. These are the plugs, and where they go, in order from top to bottom. Plug #1, jumper loop. Plug #2, jumper loop. Plug #3, to negative side of eyeball maplight. Plug #4, aka "alligator clip", to the positive side of the eyeball maplight.




wiring arrangement Wiring Arrangement.This image shows the inside of the experiment box and how the wiring was done. Simple and straightforward. Note that the short jumper wire (shown in the picture above) hasn't been installed yet.




cutout for eyeball maplight Cutout for Eyeball Maplight. This image shows the cutout in the experiment box for the eyeball maplight. The use of the eyeball requires a small locating notch to be trimmed into the opening to allow installation. You can see the notch on the bottom of the edge of the cutout.




completed assembly and slocum's 2.3 eec-iv handbook Completed Assembly and Slocum's 2.3 EEC-IV Handbook. Here is the unit in it's fully assembled form. To use the code scanner now, the cover just needs to be installed. You can see the general location of all the plugs and how much wire I used to do the job. When installed, I can put the code scanner in the storage cubby in the upper dash on the passenger side and read the codes from inside the car. For scale, Allan Slocum's book is a standard 8.5"x11".




diagram a8335-b, merkur xr4ti shop manual Diagram A8335-B, Merkur XR4Ti Shop Manual. This diagram, taken from page 4-3 in Section 4 of Group H of Engine/Emissions Diagnosis, depicts the proper wiring arrangement for the all the connections and the location of the lamp that displays the codes (replacing the analog voltmeter). The right side of this image is what we are concerned with.




sto/sti sockets STO/STI Sockets. This image shows which STO (self-test output, the big connector) and which STI (self-test input, the pig-tail, or small connector), sockets are used. Here are the socket applications, from left-to-right. Left, socket #1, output to lamp. Middle, socket #2, output to jumper/socket #3. Right, socket #3, the pig-tail, input from jumper/socket #2. That's right, the jumper goes between socket #2 and socket #3.




code scanner installed, ready to pull codes Code Scanner Installed, Ready to Pull Codes. This is the completed code scanner installed on the car. The plugs are in their appropriate STO/STI sockets and the alligator clip is hooked up to the positive side of the battery.




General fabrication information. I had to trim the male quick disconnect connectors a bit to fit into the STO/STI plugs. The wiring is simple. There are three wires total. One is a short jumper between the upper position of the STO plug (large black) to the pigtail or STI plug (small gray). The second wire goes from the lower and left position of the STO (large black) to one side of the lamp. It's a long wire. The third wire goes from the positive battery terminal (I used an alligator clip to make it easy to use) to the other side of the lamp wiring. I made the wiring long enough to put the box/lamp in the car so it's readable from the driver seat.



Final Notes. While the info and pictures here is XR4Ti specific, there is no reason why it can't be adapted to the Scorpio or any other EEC-IV Ford. The function of the EEC-IV code testing system and the general layout of the STO, STI and battery are the same.




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Published by Chris Anglin.