How To: Using the MBEC for Powered Accessories

rebelman06 · Jun 24, 2017

Subject: Using the SEO connector of the MBEC for Powered Accessories for GMT-800 (NBS) trucks
Topic Description: The MBEC (located next to the brake pedal) contains the SEO connector that can be used to power added accessories. Inside of the SEO connector, which is located next to the trailer brake connector, is several 12V+ leads and 1 ground lead. There are two always hot leads, which are 30A and 15A. These two leads are useful if you want to run an accessory without key-on or for wiring in a relay with high-amp applications (up to 30A). The SEO Ign (10A) and SEO Acc (10A) are the leads that can be used for RAP, which means your device only gets power with the various key-on positions. I find the SEO Acc pin more useful, since I don't want my accessories powered up during the cranking cycle. The SEO Acc pin is active during Accessory and Run (after engine start) while the SEO Ign pin is active while the key is in the Start (crank) or Run position.

Requirements:
*Skill Level: Basic 12V wiring knowledge required
*Time: 2 hours or less
*Special Tools: Multimeter/test light, wire stripper/crimper and/or soldering iron

The following parts are needed:
*6 Pin Female Black Delphi Packard 280 series connector P/N 12193930
*Delphi Female 280 Series Automotive connectors P/N 15317768 (~16 gauge)
--or--
Check eBay for already assembled MBEC SEO connectors

The following parts are optional:
*5 Pin SPDT relay and harness for high amp accessories
*heat shrink tubing or electrical tape

I recommend that you order several extra pins.

Step-by-Step Instructions:

Remove the round nut in the center and locate the tabs holding the cover on.

Release the second set of tabs and lift the MBEC out so you have more room to access it.

Here is a shot of the connector with the pins labeled according to my table below.

The table below shows what each pin can be used for. Before connecting an accessory to the Acc/Rap pin, make sure it will not exceed the amp rating. If it does, you will need to install a relay which can feed off of the SEO 1/2 pin or from the battery or under hood fuse block posts.

Reference shots of the connector and pins

If the accessory you plan to connect is going to draw more than 10A, you will need to purchase a 12V automotive relay as pictured below. The harness is not required, but they are not very expensive and make it safer/easier to remove or install the relay. For more information on wiring a relay, please visit http://www.the12volt.com/relays/relays.asp . The Acc pin would be the trigger, the SEO B1 or SEO B2 would be the 12+ supply, ground to ground, and finally the output pin of the relay to your accessory.

Even though I have checked and documented the pins for ground and 12V+, I highly recommend that you do the same before connecting any accessory to the MBEC in your truck. You can check the pins with a circuit tester (pictured below) or multi-meter set to 12V DC. I used both while investigating. You can check by confirming that the certain pins are always hot and that the others are hot only when the key is in the proper position. Checking will take just a few minutes, but could save your electronics if something is different on your particular model/year.

The following images are provided to inform you of where the SEO pins get their fused power from.

Conclusion: I used these pins to power a CB and as the ignition on trigger for a sound system amplifier while using the factory radio. You can power extra 12v outlets wired to the ignition (useful for GPS) or switches that are wired to relays outside of the cab for light bars and other accessories easily with this method. One way diodes are recommended by GM when using relays.

Jasen · Jun 26, 2017

Bookmarked
Nice write up.

silentbravo · Nov 18, 2019

Great resource here. I link people to this page and the GMT900 version all the time.

tomtomz · Feb 26, 2020

This is so well done - especially the marked up photos and part numbers - that I have parts on order and I plan to follow these instructions almost to the letter.

Kudos, and Thanks!

GoodenuffTX · Jul 25, 2020

Pics on writeup aren't working.

JB Long · Jul 26, 2020

Pics are working just fine that I can see. Nice way to advertise your video though, posted/uploaded today

GoodenuffTX · Jul 26, 2020

The pics are working now, but they weren't a few days ago! I tried my laptop and phone, even had my brother and wife check their phones! Glad they're up now, great write up.

callapygian · Feb 1, 2025

such a cool featue that gm included(but never mentioned) !

cloudsuck · May 13, 2025

I have 1999 Sierra and was frustrated that the Cigar/Accessory ports were always live. After much digging I came up with a pretty easy way to use ACC/Run key to control the left and center ports, while leaving the "Cigar" lighter port stock which is always on.

1) Disconnect the NEGATIVE battery terminal cable so the vehicle has no battery power.
2) Locate the MBEC and remove the black plastic nut and cover. There are a couple of side tabs that you must tease to release this cover.
3) Take a photo of your MBEC noting which connector and wiring is plugged into which socket so you can plug them back into the correct ones later.
4) Release the MBEC from the black metal mount by gently prying the right and left metal retainer tabs, then pull the whole MBEC up an off the metal mount.
5) Flip the MBEC over to the side that all the wires are plugged into.
6) Clip off the two zip ties that are around the wires that run to lower half of the MBEC..
7) On the side that the wires go into, loosen the bolt that holds the lower connector. The bolt to loosen looks like it might be the long stud that is on the front side (but it is not - it does line up with it though). Gently prise the entire connector on the wire side out of the back of the MBEC.
8) Where the wires run into the back of the connector, look for two Orange wires terminated into a single crimped push on connector. It is in Row B, hole 8 (see drawing). From the bottom edge of the MBEC go to the second row, then count eight from the left edge and that should land you at the two Orange wires crimped in a single push on connector.
9) There is a blue pin retainer comb on the side of this connector. You need to tease out. Note how it came out.
10) Go to the front side of the connector and using a pin, release the push on connector with the two Orange wires by gently pulling on the wires so it comes out the wires side (back) of the MBEC.
11) Fish these two Orange wires out of the wire bundle to get as much wire length out as possible.
12) Confirm continuity between these two Orange wires, and the center contact in the left and center power ports. These are the correct wires if there is continuity.
13) Slip some heat shrink over the bare metal of the push on connector.
14) Bring the push on connector of the two Orange wires up the back of the MBEC and over the top edge and push it onto PIN2 that is referred to in the OPs write up. This is the SEO ACCY power feed found on the front top left of the MBEC. This is what will now provide power to the Left and Center power ports.
15) Install that little blue pin retainer comb before you forget!!!
16) Reverse this procedure to reassemble everything, and you should now have key switched left and center power on the accessory ports, while the right Cigar port remains always powered.

The fuse for the Left and Center ports is in the LBEC under the left side removable cover over the fuse center and is 10A SEO ACCY. The Cigar fuse is in the under hood fuse box.

How To: Using the MBEC for Powered Accessories

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