I KNOW THIS IS AN OLD THREAD BUT ............I think I can answer a lot of questions on this issue.
My 1999 prizm headlights went out.... I spent 2 days going over this car and changed the drl module without resolving the issue. ... finally resolved it but in searching I found this same question all over the internet without one real answer ... so read on and I hope this will help.
Problem ---> headlights would turn on when you start car.... if you turned the headlight switch to parking lights they came on with the headlights ... if you turned the switch to the headlight position the headlights go out....
After dark the sensor would kick in and all lights would go out after about 15 seconds.... leaving you in the dark.
#1 LESSON LEARNED = just because the ohm meter says a ground is good doesn't mean it will hold under load.
Here is what you want to know .... power goes from headlight switch ---> thru the headlight relay and then ---> to the dimmer relay then ---> to the headlights and then ---> thru the DRL relay ---> to ground and the DRL module... (and is the key word here)
LOCATIONS =
DRL Module is behind the glove box up high in the dash .... headlight relay and dimmer relay locations will be in the 2 boxes on the drivers side of the car under the hood. .... DRL relay location is in the box on the left front under the hood.
HOW IT'S SUPPOSED TO WORK:
Turning on the Headlight Switch the Headlight relay clicks and sends power to the Dimmer relay which controls High and low beam.... power goes thru bulbs to the DRL relay and from there to ground which is shared with the DRL Module.
THE SOLUTION FOR MY PROBLEM:
If the ground on the DRL relay is not good ...things will work ... but they won't work correctly because it may or may not feed back to the DRL module ground ... see original problem above. If you unbolt the box housing for the DRL relay and pull the white plastic bottom you will have easy access to the wires and the ground wire is the white one. You can easily tap onto it with a blue connector and run an additional wire to any good ground screw in the area. My ground was intermittent .. tested good with meter but would drop under real life load.
SOME TESTING YOU CAN DO:
FIRST THING = check all grounds ... The DRL MODULE has 2 white/blk stripe wires on one end of the connector.... These grounds have been known to fail which is what kills the DRL MODULE ............ it is highly recommended to use blue splice connectors and run 2 additional wires from these wires to a fixed ground in the right passenger kickboard area .
Other locations for grounds = 1cluster on each side behind driver passenger kick panels -- 1 on each side under hood on fender wells -- 1 ground cluster in trunk at drivers tail light --
RELAYS -- you can pry the tops off and see if they look good inside -- no burnt points etc.
Plug them in with the top off and see if they engage when you start car and turn on lights. The DRL Relay and the Headlight Relay are the same so you can try switching them.
HEADLIGHTS AND DRL RELAY GROUND TEST:
If you are good with things like this then here is an easy way to test the headlights themselves.... and the DRL Relay ground.
KEY OFF -- HEADLIGHT SWITCH OFF -- If you have the DRL Module where you can get to it .. pull it. ( not required but it gets it out of the loop)
Pull the Dimmer relay... where it plugs in... the front 2 of the 4 plugs is High/low beam feed (front = towards front of car)
Pull the DRL relay ... where it plugs in ... the wider of the plugs is the switch to ground
Run a hot jumper wire from the battery + to one of the front plugs on the dimmer relay. ( just stick the wire into the plug)
(this will be one of the... high OR low beam)
Then run a jumper wire from the wider plug on the right side of the DRL relay to any good ground ...
be sure to try both plugs in the drl if the first one doesn't do anything. (one goes back to the drl and ground ... you are testing to see if this is good)
You should get headlights ... ( If you do not get headlights then you have a problem with the headlights themselves ... recheck all jumpers etc.)
Switch plugs on the dimmer to test both high and low beams. If you get both working now but they didn't when everything was plugged in then you can bet the ground is bad at the DRL relay. ... follow the directions above and put in a new ground wire.
Hope all of this information helps someone.... these wiring problems can really suck !
HOW TO DISABLE DRL MODULE:
This will keep the daylight running lights from coming on .. but your headlight switch will still control everything.
To disable DRL module ... don't cut wires -- to difficult to fix if you do it wrong ... just pull the module from it's location behind the glove box. pull the circuit board from the box you will see a number of rigid wires going from the plug receiver to the circuit board. On the top row .. cut the 3rd one from the left and bend it apart a little ... if you want to hook it back up later all you have to do is push it back together and solder it. (when plugged into the harness this rigid wire connects to a red/blue stripe wire.... check before you cut in case your car is different)