TPI  Electrical and Sensors

The aftermarket fuse box that I'm talking about is the "ATO" fuses common to virtually every car manufactured since around 1980. These fuse boxes can be found at just about every auto parts store in the country. The nice thing about them is they are modular, meaning they can be stacked together. For your stock tpi harness conversion, you may need two, depending on whether you have cold start injector circuit or not. 


The first picture shows the aftermarket ATO fuse block that will have to be used when converting with a stock tpi harness. The second picture shows the soldered connection on the ATO "gang" connector. the ganged connector can be used on the side where it feeds a number of devices off of one hot wire. The third pictures shows some of the wire connectors that may be used.

Picture above shows the difference between a good and "blown" fuse. Good fuse is on the left.  

If the circuit blows a replacement fuse, find the case of the problem and correct. NEVER bypass or use a fuse  with a higher rating. Severe damage or fire to the electrical system may occur.

Below is a drawing showing how the connections are made from a stock harness to your vehicle harness. The wire colors are only assuming you are putting this in a typical Chevrolet vehicle. If you are putting a tpi in another brand, you'll need to obtain a wiring diagram for your vehicle. You may find that the tpi harness wires to the terminals may be a different color, but don't be alarmed, just go by the terminal letters.

Dash wiring diagram    typical for 1985-89 MAF 

NOTICE: disconnect the negative side of your battery before attempting any electrical work on your vehicle. Failure to heed this warning may result in possible extensive damage to your vehicles electrical system!

When tapping into harness, fuses 1 through 4, find the large pink with black stripe wire near the steering column, a wire that goes into or close to the ignition switch, use a tester light and make sure that this wire is "hot" with the ignition key in the "on" position. The best way I would do the wires, is to cut the pnk/blk wire in two, strip the wire back about 3/16", and crimp a ring terminal on each end. The wire color to use for your tap is not important, just be sure it is a size 14 or 12 AWG (American Wire Gauge), with 12 being larger. Strip back the tap wire 3/16" and crimp a ring terminal on the end. Be sure to use the right size terminal for the size of wire. On the picture of the ato fuse box above, the long terminal strip (gang strip) is the one you want to connect the other end of the tap wire to.  When you have the ring terminals installed, you a small screw and nut to connect the terminals together and tape them up with a good quality electrical tape.  Strip the wire and crimp the wire on the end that the fuses do not attach to (see package instructions), for best results you can use a dab of solder on this end to get a good, tight connection. On the ato fuse box single (load side) connectors, tap each wire  from the tpi harness into single connector. Strip and crimp each individual wire and solder for best results        


Picture #1: the various sizes of heat shrink tubing used to seal the soldered connection from shorts and contamination. Use this on all connections, especially under the hood.  Picture #2: To begin making a good connection, strip the wires equal length, be sure to put the heat shrink of proper size on one side of wire before you twist the wires together. Be sure to keep the heat shrink as far as possible away from the end where you are doing the soldering. Picture #3: Twist the wires by crossing them over in the middle and twist outwards.                              


Picture #4: Use a moderate power iron (30-100Watts) and put the wires on non metal  hard flat surface, clean the tip of your iron first and put a dab of solder on the end to "tin" it. Put tip of iron in the middle of wire connection at a 45 degree angle for a few seconds and then put the end of the solder near the iron tip end , until the solder flows into the connection, be sure to get full penetration into the wire strands. Use a pair of pliers to squeeze any strands flat, so it will not poke holes in heat shrink tube. Picture #5: Pull the heat shrink over the soldered connection with the ends evenly spaced from the middle of the connection. Use a low heat source,( the larger end of soldering iron can also be used) and heat the shrink wrap until it forms a tight seal, be especially careful not to burn the shrink wrap, or you will be doing it over. Picture#6: Shows the soldered connection to the ato fuse gang connector. Notice where the wire is crimped and the soldered end.


When tapping for the cold start injector (on 1985-88 harnesses only), use the appropriate size wire(12-14 AWG). You'll have to gang a another ato fuse block onto the first one. Find the purple or yellow wire by the ignition switch, and cut it into two, strip back the wires 3/16" and crimp the ring terminals on. Put a ring terminal on one end of your tap wire on the  other end attached to the gang strip, crimp and solder. On the load side terminal, strip and crimp the wire from the tpi harness (terminal "R").

When the wires are all attached to the appropriate terminals, with the front of the ato fuse holder facing you (fuse end) put the hot wire side of the gang terminals in the fuse block on the left side of the first fuse holder, the same for the gang terminal in the second block if you have cold start injector circuit, otherwise disregard this step. The terminal strips insert from the back side and snap into place. Then with the first block, on the right side is where the individual fuse connectors will attached. Put each individual holder in place, you may want to make a diagram or label to show what fuse goes where.

Depending where you want to attach the ato fuse box at, will determine how long the wires will be. If you have pulled the tpi harness from a donor car, make sure that the under dash wires you cut from the donor car fuse box is as close to the fuse box as to allow you more flexibility in choosing a location for the ato fuse box that will make it readily available. The same for the tap wires, make sure they are long enough to allow for easy installation of the fuse box. The best location will be next to your existing fuse box if space allows.

Most aftermarket harnesses just have three or four wires to attached to the electrical system. A constant +12V hot (usually red or orange wire), a +12V switched ignition on (usually pink or pink/black wire). Also a purple wire to attach to the +12V hot only in start for the cold start injector, the late maf (1989) harness or speed density system will not have cold start injector, and a white or tan wire to run to the fuel tank. The wire for the fuel pump is best to be run along under the carpet protected by the sill plate, along the back trim panel behind the back seat. Drill a small hole to pass the wire through and use a rubber grommet that appropriate size to protect the wire, then you can make your connections to your fuel pump.


Mount your ALDL connector in a place where it is accessible.

Also, consider the type and location of your check engine lamp. It should be mounted in a spot where it can easily get your attention, just in case something goes wrong. You could mount it next to your ALDL connector. There are many aftermarket lamp packages that are self contained. You can also use a small led light that can be mounted on your gauge cluster or console. The one thing you need to remember about a led, that it normally uses a voltage far below the 12 volts in the automotive system, usually around 1.5-3.0V. When you select your led lamp, look on the package for the current rating and voltage of the led. Look at the example below:


Mount your ecm in a spot where it also can be easily accessible. Use the mounting bracket or get one from a salvage yard that has a way to mount the ecm to a heater box or side panel or firewall. Just be sure to mount it high enough out of the way so it won't accidentally get kicked.

This is the location of  my ecm and relays common to a aftermarket set up.

Another thing you'll need to do is to add the TCC lock up disengagement switch for the overdrive (2004R or 700R4) if you decide to use this transmission. The switch is the one that has a connector with a purple and pnk/blk wire on it. If you get one from a salvage yard, be sure to get enough wire to connect to your tpi harness connection.

NOTICE!!  One final note before you hook your battery power to your harness for the first time. Double check ALL your connections for tightness, and make sure they are secured out of the way of anything that may cause it fail, either by excessive heat or vibration.

Make sure your sensor wiring is secured and routed as far as practical from any heat source and from your spark plug wires and ignition coil lead.

If you are using your old alternator, check to see if it is rated for a minimum of 70 amps. Your old 63 amp (or less) alternator will not cut it. Fuel injection systems are power hungry considering all that must be powered up- the ecm, fuel pump, sensors, actuators, fuel injectors. With a low amp alternator, the power output will not be enough to keep the battery properly charged, especially on a cold, wet night with all the lights, heater and windshield wipers operating at the same time.


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