BMW 502 Race Preperation

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Electrical System—Body Electrics

You'll remember that the stock battery lived on a shelf in the engine compartment where it slowly corroded its way through all the metal in its neighborhood. We have relocated the battery to a plastic box in the roomy trunk to improve weight distribution and get it out of the way. We have used the positive battery cable system from an E30 325i, which comes stock with a trunk-mounted battery. We also installed a rules-required outside battery switch which allows rescue personel to shut off the complete electrical system in case of emergency. 

The stock fuse box is very simple, containing just 6 fused circuits and no provision for relays or future expansion. More sensible people would have added a small supplemental fuse box and put in relays wherever the need arose. Having never been accused of sensibility in these matters, we added a complete fuse box assembly from a mid-eighties 325e, giving us plenty of circuits, plenty of relays, and plenty of flexibility. Wherever possible throughout the rest of the car we have tried to upgrade and update to gain reliability. For example, we were often able to replace old switches, relays, and wiring with equivalent parts from later model BMWs. The column mounted turn signal, headlight, and wiper switches from an E21 320i now reliably and cheaply perform all those functions in the 502. Headlights, driving lights, and horns are all modern, as are the wires and relays that supply them. Most of the rest of the stock body electrics were superfluous to our purpose and have been removed.

The charging system is another area of significant upgrade. The stock generator and separate regulator have been discarded along with their complete wiring harness. After examination of our electrical needs and the space constraints at the front of the engine, we chose an internally regulated 65 amp alternator from an E28 528e, located it on the engine so that the belts would line up properly, and fabricated overly strong brackets. Alternator wiring is much simpler than that of the old generator and regulator.

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