alternater help needed

[pumpkinman 0]

just installed a brand new chevy alt on my mecury van , its chargeing but not fully i ran over my DMM so i cant test it till tomorrow.. theres 2 wires on the alt one is grey the other is white.. 3rd wire is the big red battery wire.. the gray im told is to battery power and white is a exciter wire but am told you dont have to use this white wire because at 1200 rpm itll turn on.. so a quick test and it was chargeing but i was using a test light for the time being and it was lit but not as bright as the vans own alt when i hooked it to van alt it was bright.. not as bright with second chevy alt .. any one have a clue why its not fully chargeing or am i missing something.. its a small case gm alt originally for a chevy cavalier.. bolted on fine.. this alt will be runnning only my amps battery bank.. . maybe theres a good wiring man here,, ps im told to just hook the grey wire to the battery but after car is off theres still power to alt is this not correct and something about using a bulb as a resistor on white wire to excite the alt hows that done.. thanks so much all..

[Tirefryr 1,742]

If you don't have the exciter wire hooked up, the alt is not charging. If it is, you have the wiring switched or it's self-exciting.