Which ends to swap?

[SMEGMA STENCH]

I'm upgrading my 1987 Silverado's headlights from the typical factory sealed headlight, to some headlights that will accept H4 bulbs. The factory connector on the truck already fits an H4 type bulb perfectly, but the "pins" in the connectors are in the wrong spot. They don't correspond to the prongs on the H4 bulb. I'm just going to move the pins around to the right spot. But how do I figure out where to move them to? The bulbs don't come labeled, so I won't know how to rearrange the pins so that they properly power the new H4 bulb. Yeah I suck at electricity. Figured this one would be an easy one for you electrician types.

[forbes]

use a test light to identify which leads do what. then use a bettery to determine the bulb. the ground on the buld should be obvious

[SMEGMA STENCH]

Ok so obviously you got a ground, and you got a power. What would the third prong be for? Perhaps the bright lights? Some bulbs have both bright and dim in one.

[SMEGMA STENCH]

Wait does anyone know if H1 bulbs happen to fit inside an H4 socket?

[racrguy]

You have ground, high and low beams.

[YALE]

Surely there's an EVTM (or whatever GM calls them) for that vehicle.

[SMEGMA STENCH]

Electrical and vacuum troublshooting manual? Yeah I looked around but it seems they want you to pay lol. But in this instance, I'm not sure if I need it. Although I did fail to take into consideration that the factory sealed units... I don't know. For some reason on this truck, when you turn on the brights, all 4 headlights come on. Makes me wonder if there is even any difference between the bright and the dim bulbs for this truck. Its one of those 4-eye 87 silverados.