Low beam issues.

What would cause my low beams to switch back and forth between each other? What i mean by this is, it seems like every time i change my bulb the other one will stop working. And its not like its blowing the bulb either.
I took a look at it on the weekend and cleaned the relays because of green build up. After i cleaned the relays, the one low beam that wasnt working, all of a sudden worked, and the other one stopped working.??????? And my highbeams work fine.

Do i need a new relays, or is this a much larger issue that i shouldnt even bother wasting time with.

Thanks

 

When the low beams 'switch', do you mean:

(a) one or the other goes totally 'dead' (no light at all)
OR
(b) one or the other is in high beam mode (instead of totally 'dead')

If it's (b), and this Taco was originally a Canadian model, I'd suspect a short in the main DRL Relay (not the DRL Relay No. 4) or the wiring connected to it.

If it's (a) and this Taco was originally a Canadian model, it's probably the wiring.

 

Originally a american truck brought in the late 90's, But has the Km's. The working low beam will always go out when ever i change the non-working light. Highbeams work fine, no matter what i do.