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Fooling the Autocheck System

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Once you rewire your lights, the autocheck system will constantly complain about a burnt out bulb (as if you couldn't figure it out yourself!). Here is a procedure for permanently disabling (fooling, actually) the headlight circuit of the autocheck system. It's all done to one suspicious looking relay location.

The unit in question is located in the auxiliary relay panel, under the dash. Middle row, first on the right (position #6), looks like a standard Hella relay. It is not. It's is a logic controller, P/N 443 919 469B, built around a single chip (either a difference amplifier or a comparator, ULX245M a proprietary SOB). The chip listens to the current that flows through two very low reference resistors, comprised out of two 15mm wires no less than 1mm in dia, probably Ag (they are silver colour and have a very low resistance). The circuit listens to the impedances of the low beams filaments and throws a red flag (6v on terminal "K", goes to a thin grey wire, that is connected to the computer) if either of two conditions are met: 1. At least one filament is blown (R=infinity) or 2. R of one filament significantly differs from R of another one.

You want to shunt those calibrated reference wires. You need to connect 56bR to 56bR1 and connect 56bL to 56bL1. To do this without damaging the original controller, take an old (a burnt one is OK too) standard 4 or 5pin relay and gut it out. Then solder it's terminals in pairs so that when plugged in place of the OEM controller, the headlight circuits are complete, and the computer has no signal to cause it to cry. Or you can just pull the logic controller and make two short (3") jumper cables of 14-ga. wire, with a male spade bit (blue code) on each end. Then insert the spade bits into the relay connections to jumper both headlight circuits. Either way, the two smaller jacks in the controller socket, 31 and K, will be unused, so that the computer won't see a red flag on terminal K and be happy.

(I don't have a relay in front of me and don't want to mislead you. You figure it out, either 85+30 and 86+87 or 85+87 and 86+30. BE CAREFUL, try not to screw up here! Use a thick wire for soldering).

The diagram for the relay panel may mention that this relay position is also for oil pressure warning. That is true only for cars without the autocheck computer. If you do have the autocheck computer (and you do, otherwise you wouldn't be reading this section!), the oil pressure signals go straight into the autocheck unit in the instrument cluster, so this modification will not disable any autocheck functions other than the headlight warning.