Following up on lucid's excellent post.

I'm pretty sure Stern's kit plugs into the existing headlight connectors.
It also will use clean strong connections to battery power and to ground.

This way the complete original system that lucid described now only has to operate relays, instead of power-hungry bulbs. The relays serve as electrically controlled switches that deliver battery power directly to the headlights.

With this arrangement, the bulb failure warning sensor will only see the relays in the headlight circuit, not the bulbs. Other circuits will be monitored as originally intended (brake and tail lights).
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns, tach, small clock. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.