i first bought the truck and noticed when it got dark that all the lights (headlights, dash lights) were very dim. i had an alternator belt that was going so i figured that it might just be not getting enough power? changed the belt and nothing changed, should i consider replacing all bulbs or upgrading something like battery or alternator? dome light and tail lights work fine. thanks in advance!

 

Use a Volt meter, best $20 you will ever spend

Test battery, engine off
Should be 12.3-12.8volts
12.8v is a new battery
12.3v is a 5 to 6 year old battery and time to shop for battery sale

But battery has nothing to do with lights when engine is running
The battery is ONLY used to start the engine, thats it, then everything is running off alternator power

Start engine
Test voltage at battery again, this will be alternator voltage not battery voltage
Should be 14.3 to 14.8volts
Let engine idle for 5 to 10minutes then test again
Should now be 13.5-13.8volts, about 1 volt lower that just after startup, and 1 volt HIGHER than "battery voltage"

Now turn on the headlights and turn heater fan to high
Test voltage again, should never go below 13.5volts, if it does you have a bad Field in the alternator, there are 3 fields, so with 1 bad field alternator only has 2/3s power output

If voltage all checks out then all is well with charging system
If not then you have a problem, let us know exact voltages


Because the dash lights and head lights run through the Main Light Switch it could have corroded connections that only effect those lights
The dash lights do have a dimmer which I assume you can adjust, rotate the headlight switch clockwise?

Taillights use a different wire from the main light switch so they may be OK, but other wires are not

The main light switch does need to pass a lot of AMPS so they did fail over the years, not uncommon at 30 years old to have to replace one