Crank but wont start

[Lifted2x]

Well I got myself involved in another mess of a truck. It is a 90 cab and engine(4.0) with a 86 frame, trans, TC and axles. It looks like the person that did the work did a good job there isnt any splices or bad wiring. But now that its all together there is something that is not working right. It has power where it should and I already checked all the fuses. But it doesnt have any spark. When I connect a test light to pull the codes it is very dim (low voltage) and will not do anything other than shut off when the key is turned on. (it does this with the ecm removed also) I checked for power to the ecm and it has power and I can trigger the fuel pump through the pins. But still nothing I have even replace the ecm from another truck but that didnt work. Any Ideas?