Climbing a ladder is not a smart idea after your first trimester. I spotlight at a dinner theater, so I have to climb 3 different ladders 4 times a day and on double days I have to climb it 8 times. And the docs told me after 3 months "No more climbing" it's too much strain on your uterus. As far as carrying heavy objects... They say if you did it before continue on until you feel the first real strain. I carry 30-40lbs of plates, food, and lids on a tray several times a day and I'm doing just fine. In fact it has helped me to get an appetite after morning sickness. Just be super careful not to go too long without food in your tummy. Hope this was helpful :)
I would definitely talk to your doctor. I think for the 1st trimester you will be ok, just really have to watch how much weight u lift at a time and probably shouldn't wear your heavy tool belt. As you progress, depending on if you have any other complications or not, you may have to reduce how much you're up and down a ladder, again how much you lift, etc. And as your belly grows, it will be harder and harder to fit into some of the areas you need to for pulling wire, etc. And of course there is always risk of an electrical shock.
Again, definitely talk to your ob. They may limit your work early.