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Technical_   Interior_  On Board Computer (OBC) Retrofit

On Board Computer (OBC) Retrofit
Fred Kim

If you're one of those guys who bought a 325 (or a two-door 325i) with the basic 6-button clock, then you're probably envious of all the other guys who are always bragging about knowing their average miles per gallon over a long trip, or knowing how much longer they can go without filling up. Well, now you too can be a bragger! Retrofitting an OBC onto your car is a pretty simple task, but it's just a little time consuming.

(For you 318i guys, I tested a 325e OBC with an M10 318i instrument cluster and all the readings seem accurate. If your car has an OBC relay and an ambient temperature sensor, then I believe this conversion will work for you.)


WHAT YOU NEED

  • OBC from same type of car (eta owners pull one off a 325e/325es, 325i owners need one off a 325i/325is. An OBC from a 5, 6, or 7 series will not work.)
  • complete OBC wiring harness (BMW part number 61 12 1 385 795. This runs from the OBC to the back of the instrument cluster, then splits off and connects into several relays under the dash. The harness can come off any year E30, so long as the donor car came from the factory with an OBC.)
  • OBC backlight (BMW part number 65-81-1-375-461)
  • keypad bulb (BMW part number 62-11-1-368-299)
  • factory screwdriver
  • smaller #2 Phillips screwdriver
  • pliers
  • anti-theft radio puller (for factory BMW radios)
  • Bentley manual (optional)
  • lots of patience

ESTIMATED COSTS
I was lucky and bought my OBC for the low price of $30 from Dustin Wunderlich. Most junkyards sell them for around $60, and I've seen online wreckers sell them for as high as $100. Shop around for these things.

I purchased a wiring harness from a local junkyard for $37. I pulled it out myself, which may have saved me some money. I'd estimate that they would go for about $50 elsewhere.

The OBC backlight came from my local dealer, who charged me an unbelievable $33.93 for it. I've heard most dealers sell them for about $25. The keypad bulb is $0.72.


PROCEDURE
1) First open the glovebox and remove the upper black plastic cover by removing the front 5 screws and taking out the two clips located on the left and right sides of it. Unhook the two prongs that connect to the light. Unhook the glovebox door by removing the two straps from its housing, then let it rest on the floor. (To avoid a mess it may help to remove the contents of it first.) Remove the right black plastic dashboard panel (adjacent to the glovebox) by removing the clip located towards the floor, then slowly wiggling it out of its position.

2) If you have a factory BMW radio, pop out the two tabs on the side and use the anti-theft puller to remove it. If you have an aftermarket radio, reach in from behind the dash and slowly push it out. (If you have an older Alpine, use a ballpoint pen and release the two tabs on the front.) Disconnect the wiring harness and power supply and set it aside. It may be helpful to remove the metal dashplate that holds the head unit in place.

3) Reach in from behind the dash and pop out the button closest to the clock. For me, it was the circuit breaker, but on your car it may be the defrost or hazards.

4) Flip up the switch on the back of the clock and pull out the green plug.There are 4 screws holding the clock in place, one on each corner. It is not necessary to remove the screws completely, so try to leave them partially unscrewed. If you do happen to take them out, be extremely careful that it doesn't fall into the bottom of the dashboard, where it will never be seen again. (Trust me, you will never see it again, so be careful. I've tried looking.) Now slowly remove the clock, taking care not to wiggle it excessively (otherwise the screws will fall out, duh) and replace it with your new OBC. Once it is in place, retighten all 4 screws.

4a) By now, you should have replaced the backlight with a new unit, because nothing is worse than finishing the installation only to realize that you can't read anything because of a burned out bulb. If you didn't change the bulb, now's the time: Using a pair of pliers, grab the white tab on the right side of the OBC and pull out the old housing and replace it with a new one. Also, using a pair of needle-nosed pliers, change the bulb behind the 13-button keypad to avoid future hassles.

5) On the driver's side of the car, remove the lower knee bolster by taking out the three thumbscrews and sliding the plastic hook out from underneath. Disconnect the door gong. Remove the plastic dashboard trim (just below the cluster and behind the steering wheel) by taking out the two silver knurled nuts from behind the dashboard. They are located on the left and right sides of the panel. Remove the instrument cluster trim plate by taking out the four lower and two upper screws. The small Phillips screwdriver is necessary here. To take out the instrument cluster, remove the two retaining screws and slide it out. For best results, gently grab the two "rabbit ears" (where the screws were) and pull from there, but don't use too much brute force or you may break it right off. If you decide to leave the steering wheel in place, then it's probably easiest to slide the cluster out the left side.

5a) Removal of the steering wheel is optional. I didn't bother with it, but it may help if you don't know what you are doing and/or want a better view of the cluster's backside. To remove a non-airbag steering wheel (note: if you have an airbag and you've gotten this far, leave the damn thing in and go to Step 6), use a small flathead screwdriver and carefully pry off the BMW emblem. Center the steering wheel and mark off its position so it will be aligned properly when reinstalled. Hold the wheel and remove the nut and washer. Insert the key into the ignition and turn it to the first position, then pull the wheel off the column and disconnect the wires from the horn pad. Be sure to turn the key to the off position before connecting the OBC.

6) On the back of the instrument cluster you will see a yellow connector in the center. Release the black plastic tab in the center of the connector then remove it from the cluster. This harness runs to the 6-button clock that you should have removed by now. If you are lazy then you can leave it in there and tuck it away, but if you are anal retentative like me and want them out, you have to unclip the five or six wire ties that connect it to the rest of the dashboard harness, pull it out, then reclip them. It's kind of a pain but no harm is done by leaving it in place.

7) Take the new wiring harness and plug its yellow connector behind the cluster, then wire it through the dashboard and plug the green connector to the back of the OBC. Make sure the black tab is down to lock the connector in place. At the other end of the harness, you will see four connectors (black, green, blue, and white). Wire them down the left side of the dashboard.

BLACK CONNECTOR: Plugs into the right slot of the door gong and is used for low temperature and maximum mileage features.

GREEN CONNECTOR: Plugs into the fuel pump connector and is used for the CODE feature. Also supplies a feed to the auxiliary horn (which must be added); not necessary if you are don't want the feature active.

BLUE CONNECTOR: Plugs into the turn signal stalk and is used for the OBC remote control feature. If youd don't install the turn signal, then you don't need it.

WHITE CONNECTOR: Plugs into the ambient temperature sensor.

Since I have an aftermarket alarm, I don't want the CODE feature activated so I just tied the green one out of sight with electrical tape.

7a) There are some additional features used on the OBC, such as a turn-stalk switch (which also requires an additional harness and relay) and the auxiliary alarm horn. Neither is necessary for use, though I did install the remote control turn signal switch. To install this, remove the steering wheel as described above and remove the lower steering column cover by removing the two lower and two frontal Phillips screws. Unplug the ground connector and slide out the turn signal relay from the column. Trace the wires under the column and disconnect it from the main harness. Install the new turn signal switch and wire the blue connector to the one from the OBC harness.

8) Installation is pretty much the opposite of removal. When reinstalling the instrument cluster, be careful not to break off the tabs and make sure the back of it is cleared of any loose wires/connectors otherwise it won't fit properly. When you turn the key on, the OBC display should read "UHR." To set it to proper time/units, read your owner's manual or click here.

Now enjoy your new OBC, and try not to fiddle with it too much on the road. Ten minutes after installing it I almost wrecked my car because I was paying too much attention to my miles per gallon.


Thanks to Jonathan Lyster-Clayton for information regarding that mysterious green plug.


LEGAL DISCLAIMER: I am not responsible for anything that may go wrong with this installation. If you cut some wires, lose screws, or if your engine mysteriously self-destructs, I am in not liable for any reason. You are doing this conversion at your own risk. Sorry, gotta watch my back.

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