Thought the red (handbrake) light was tied in with the yellow abs one anyway.

When you removed the abs you should have unplugged the the abs sensors - most probably at the yellow connector. You need to bridge the two pins within the end of the yellow connector on the end of the loom as keeping contact between these keeps the abs light out.

If you mean the oil presure light - then it is possible you have pulled the connector from the sensor on the back of the engine when removing the abs.