How much of the engine did you actually replace? For instance, if all the original manifolds and accessories were bolted back on, then I would look for something electrical left disconnected, like a ground strap or a plug/socket somewhere. If it was a complete used engine, then there may also be some incompatibilities of controls/sensors.

Check missing ground strap first, though, since the lights get bright/dim.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7