My old trusted Paj is giving me a weird issue

When Idling and a a standstill, my engine light comes on, then goes off, then come on with the two other lights mentioned. Then they stay on for a while and the all go off again.
This seems to be 80% quicker when I use my airconditioner.
The car runs fine, breaks fine, I cannot detect any other issues.
2003 DID LWB.
Agents in Kuilsriver suggested I check the battery, I did that. Auto electrician recons it's the booster pump without having opened and testing anything.Ligts acting strange
Any advice from anyone?