Body Control Module

This write up talks about how I installed a 98-01 Blazer / Jimmy / Bravada Body Control Module (BCM) in my Fiero.  There is already a write up on how to install the 4th gen Camaro BCM in a Fiero.  The write up is very informative and well done.  Hat tip to Oliver Scholz.  Just like him, I wanted a stock looking remote.  I didn’t want as many features as the BCM has to offer, so in the end I have keyless entry, keyless trunk, parking lights that flash with the alarm or the unlock, a horn honk with the alarm or double press of the lock button, a different louder chime for a few features, and lockout protection.

The Pros

The big advantage to this BCM over the Camaro BCM is that it does not require very much dissecting of your car’s wiring to install with these instructions.  You will not have to remove the dash.  In fact, you will only need to make 4 splices into the Fiero’s harness: Lock, unlock, parking lights, and trunk relay.  All of the work inside the Fiero could probably be completed in less than 2 hours.  The majority of the harness can be built sitting at a desk in comfort with a soldering iron and the right tools. Another big advantage of this BCM and the way I chose to wire it is that you can completely unplug the BCM and everything on the car will still work.  It is installed in parallel to the car’s factory controls.  Remotes can be programmed in the car using the same procedure as the Trailblazer, but instead of using the unlock button on your car door there is a button on my relay module that acts like pressing the unlock button to the BCM.

The Cons

The Trailblazer BCM has only one big draw back, not all BCM’s for the Trailblazer have the alarm feature.  There is probably a way to get these BCM’s reflashed to include it, but I think that requires a dealer connection that I do not have.  If you are reading this and know a guy, let me know.  I have about half a dozen BCM’s sitting around without the alarm feature.  It also does not have a security light like the Camaro BCM, or a shock sensor.  I’m usually parked in a garage and don’t think the flashing light does much to scare off thieves anyways.

Custom Relay Module


To simplify the install I designed a circuit board.  It uses relays from the Trailblazer and 3 parts from  The button, part number HP0215AFKP2-S, sends the unlock button to the BCM.  It is only used for reprogramming new remotes as mentioned earlier.  The switch, part number M2011SS1W01 UC, sends power to the BCM, relays, receiver module, basically all the extra hardware for this install.  The diode, part number 1N4148FS-ND, tricks the BCM’s light sensor so that it only uses the parking lights when the alarm is going off or the remote’s unlock button is pressed.

The circuit board was designed using ExpressPCB’s free printed circuit board software, which locks you into using their build service.  That is fine since they are very competitively priced.  Download the file to recreate the circuit board here: FieroBCMConnectorV01.PCB.  All the pins are pretty clearly labeled with where they go.

Here is a crude diagram of how the BCM is wired into the car:

That was done before I designed the circuit board for the relays.  If you have some faith that the circuit board is built correctly and follow it exactly you will not need a diagram.

How to do it

1) Go to the junkyard and gather these parts:

Bigger picture of parts, click here.

If you find a Trailblazer without a receiver module then it is likely that the BCM does not have the remote functionality.  Make sure to grab as much of the wire as possible to avoid soldering too many extensions.  If you can’t find a Fiero in a junkyard, try a Beretta or Grand Am from the early 90’s.  I found these connectors in one of those two, but they were missing a couple pins, so I had to find two sets and shuffle some pins around.

2) Get a circuit board from me, order your own from ExpressPCB, or wing it using the harness diagram above.

3) Assemble C210 and C201 with the wires tapped into that you need for the BCM.  This is how I made the claim that I only tapped into 4 wires in the car.  There are several other wires I used, but this method let me plug in a connector instead of completely hacking up the harness.

The wiring for C210 is not simply taping into it, some wires are unplugged or intersected, so pay attention to the diagram.  The note on the relay circuit board tries to capture this by saying body, wheel, or both.  Body means that it is wired into only the body side of the connector, wheel means it only goes to the steering wheel side of the connector, and both means the wire connects from steering wheel to body and it is tapped into it.  I tried to capture this in the diagram, so have a close look at C210 as it is drawn there.  The wires in C201 are all passed through and simply tapped into; very simple.

C201 — A: Ajar Switches Doors — B: Battery CTSY/LID 25A fuse — C: Seatbelts switch ground — D: Parking Brake switch ground — E: Ajar Switches — F: Between Key in IGN and Door Jamb — G: Brake switch signal — H: Ground G201 back of steering column

C210 — P: Brake switch signal — N: Right turn to cluster — M: Left turn to cluster — L: Turn flasher to Hazard assembly — K: Hazard flasher to Hazard assembly — J: Right turn indicator — H: Left turn indicator — G: Horn (ground to activate) — F: Between Key-in-IGN and chime — E: Between Key-in-IGN and door jamb — D: (empty)

4) Put as much of it together before going into the car as possible, like this:

The lengths I have in this picture worked out great.  If you scroll ahead in the instructions you will see a picture of the Relay module bolted to the BCM.  You can use that as your guide to BCM wire lengths.  The ignition line and C201 are about 18 inches long.  C210 is about 24 inches long.  The only suggestion I have is to make the receiver wires longer than 18 inches so it is in a better location for reception.  Try out a few different locations to see what works best.  I have not tried moving mine around much but the reception seems weak at times.

5) Disconnect the battery before working on your car’s wiring. Find the trunk relay on the right side of the steering column and tap a wire in to pin C.  Make sure the wire is long enough to reach to the BCM’s location.  Repeat this for the the light switch, pin E.  If you are lucky you can snake a wire down to the BCM without taking apart very much of the cluster.  It might be easier to snake the wire up to the light switch and then tap it in.   Again, do the same for the interconnect C307, the one near the fuse panel that connects the driver side door, pins C and D.

6) Solder those 4 wires in the right place on the circuit board and plug in C201, C210, and the ignition wire.  That ignition wire fuse panel connector was hard to find in the junyard by the way.  You could get by with just a simple crimp-on quick disconnect like this: When you are done you will have something like this:

Some well place zip ties and spiral wrap wire loom make for a clean install.

7)  Secure the relay module to case of the BCM.  There are plastic tabs on the side of the case to pop it open.  Drill two holes and use some 4-40 bolts to hold it down. Nylon bolts would be better than metal for this application. Maybe even the small plastic push pins would work too, sometimes called Christmas trees.

8) Replace the door ajar light with an LED.  This is necessary for the alarm to work.  Without it the door ajar indicator to the BCM is not working properly and will never think the doors are shut correctly.  Most LED’s and a resistor in the range of 680 to 1kohm will work just fine.  I simply soldered those into the OEM bulb socket for the cluster.  Just make sure you install it in the right direction, or else it will never turn on.

9) Reconnect the battery and make sure everything still works in the car (locks, key, ignition, parking lights, horn, and trunk) and switch on the BCM power at the relay module.  No sparks or smoke?  Good.

10) Get your remotes programmed.  GM part number 15732805. Sit in the car with the doors closed.  Put the key in the ignition.  Hold down the unlock button on the relay module while you turn the key to on, then off, then on, then off.  Let go of the button and the doors should lock and unlock again to signal the BCM is ready to program the remotes.  Hold the lock and unlock buttons on a remote until the BCM locks and unlocks the doors, signaling it has learned the remote.  Repeat for the next remote.  Turn the key to on to end programming.  Take the key out and test the remotes.  Like it says, press the rear twice to pop the trunk.

10) Lastly, where does the BCM fit?  Right behind the fuse panel worked fine for me.  I didn’t even have to zip tie it up to get it fitting nice and securely.

11) Figure out if the alarm works.  Roll down a window. Close both doors, the hood, and the decklid. Press the lock button on the remote.  Count to 15 or any amount of seconds greater than 15.  Reach into the car and unlock the door.  As soon as you open it the horn and parking lights should start doing their little dance.  If not, then sorry, your BCM does not have an alarm.

My car does not have carpet or several of the interior parts as you can see.  I don’t think that should make the install too much different for the rest of you.  Do your homework if you have any other Fiero besides an 88 GT.  Don’t count on me to save you if anything goes wrong either 🙂

If you are interested in purchasing a single board with the 3 Digikey parts and a new door ajar light from me directly, leave me a reply and I will try to help.  Plan on spending about $50.

One Response to Body Control Module

  1. Issac says:

    Great write up and looks professionally done/thought out….not just a hack. Definitely something I can see being a great reference for Fiero and other 80’s GM owners.

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