I do not know about an 1800, but it works on my 80 GL1100 and 83 Aspencade. Does the 1800 have the single adjustable antenna? If so, it will probably work, but I would NOT key it until I got the SWR's adjusted. You could easily burn out the reception. Also, you MUST groung the Antenna Heavily. Radio Shack has the Antenna to CB connector.
Adapter is Motorola female to PL259 male, but you'll probably need a patch cable won't you?Better to change the connectors to 259s while your at it though. A center-loaded CB antenna on a motorcycle is looking for 8.5' of ground to radiate off of... and it aint there, so help it out in any way you can.