You might find this URL useful:
http://www.***.com/asiaoverland2000/Bordersingmalay.html
Leaving Singapore:
- Immigration: Give the passports and the necessary cards (green card for EP/DP holders, work permit card, etc). Put in the cashcard into the machine to pay the tolls.
- Customs: drive slowly and be prepared to stop unless if the customs guy waves you through. They will also randomly check your fuel gauge for the 3/4 tank rule.
Entering Malaysia:
- Immigration: present the passport and the duly completed Malaysian immigration card. If you don't have the immigration card, pull over before the immigration booth and get the cards from the booth, fill in the cards and re-join the queue. Note that if you need visa to enter Malaysia, you need to apply for the visa in advance at the Malaysian high comm at Jervois Road, off River Valley Road.
- Customs: similar to when you're leaving Singapore. Drive slowly and be prepared to stop unless the customs guy waves you through.
Hope this helps. Thanks.