this used to happen with my old 1995 volvo fl10 wendy house.
when i was hooked on to my trailor no abs warning light, but when hooked on to my gaffers curton sider i used to get the warning light, and was told it was an incompatability thing dont worry about it.
when hooked up to older trailors with no abs the light would come on as the abs suzie couldnt register anything so it told me there was a fault when i asked our fitter he told me it was normal, being a bit green i thought it was ok.
i never used to swap very often being a bulk tip operation but we used to sub for another company on traction work and the light always used to go on and off with different trailors so is the incompatabilty thing right or wrong, or is the fl10 a bucket of pooh (retorical question 
)
chris
my amber abs light is on ( ref the unit ) its been in to the dealers for diagnostics ( i watched the technician do it ,very clever!) it says there is a fault with the ecu, not the abs, where would i stand with that?
regards
paul
3 points & £1000 fine according to our fleet engineer
UnionJack:
3 points & £1000 fine according to our fleet engineer
Fleet Engineers often talk out of their rears UJ. If he screws up, you think its your fault, from what you’ve put here mate. That way you will put your hand up (probably inadvertantly), when you’re talking to the people who pull you.
Some older trailers have incompatability problems with modern ABS systems. They show an amber warning light on your dash. Get it checked at the dealers as soon as you can. If the red ABS warning light comes on (yes you HAVE got one) stop.