1984 GT interior light issue

I was looking around and couldn't seem to come up with an answer for this. I have an 84 GT the interior lights and map light are very dim, almost look like when you have a dead battery. so dim that at night if i turn them on or use the map light i need to holds something 6" away from them to get any amount of light to see. I thought maybe the battery, but with the engine running, or with jumper cables hooked up the lights dont change, not even a little. this is a bit frustrating as my other 84 GT interior lights are so bright you need sunglasses. both cars are stock. what else should i check? voltage regulator maybe?