Headlights cause car to loose 4th gear

[Eych]

Ive been having some weird electrical problems like slipping and struggling changing gears and then when I was on my way home the other night I lost 4th and had to drive home in 3rd but if I turn off the car and turn back on its back for a little bit and then just drops out but then driving during the day without the headlights the gears are still struggling but don't loose any gears, I had some water leaking out from under dash cause of a broken seal thought it might have caused some sort of electrical fault, but not really sure I've already had a transducer replaced cause car wasnt up shifting and now this I'm so annoyed!
It is a 98 VT acclaim with an automatic transmission!
Any ideas what's the problem?