headlights, taillights electrical problem

I have a 1996 tacoma 4x4 w/ downey lift, front and rear bumpers and headers, TRD Supercharged with bored throttle body, K&N intake, injectors, high flow cat and Borla Catback exhaust in other words its my baby. I am having a serious problem in that my headlights will only allow me to flash the brights by pulling back on the headlight/turnsignal lever. The regular headlights and brights will not turn on. Nor will the tailights. Ive checked all the fuses, ive replaced the bulbs more than once, there is power to the HEAD relay although i dont know how to determine if its functional or not, its a toyota brand relay with 4 male ends, does anyone know where to go from here!!!??

Remove the relay. Check the voltage on the female terminals in the relay plug. The should be 12 volts on one small and one big terminal. Use a jumper wire between the two big female terminals, it should be a fair sized wire because it will carry the headlight current. Do the lights now work? If they do check the relay as follows. The Toyota relay should have two big and two small terminals. The small terminals are the switching terminals for the relay coil. If you have a battery charger or any 12 volt supply you can check relay coil operation. Hook the red battery charger clip to one small terminal and the black clip to the other small terminal, polarity doesn't matter on a relay. You should hear or feel the relay coil energize. If you have an ohmmeter check that there is 0 ohms resistance accross the two big terminals. You could also run a jumper from the small terminal with the red battery charger clip to one of the big terminals and measure the voltage on the opposite big terminal, it should have the same voltage on both sides. You really need wiring diagrams for your truck top locate the problem. I'm linking you to a 2003 shop manual, it should be close enough to your lighting circuits to help.
http://fsm.afraid.org/
Look for headlamp circuits in the wiring diagram to get an idea of the wiring layout. The tail lights are on another diagram. You should have another relay in the tail lights. You can look at the lighting circuits in volume II to get some ideas on testing each component.

Note there are separate relays, fuses and bulbs in the two lighting systems. The common components are the ECU, (2003, I assume 96 is similar), light switch and ground circuits into the switch.

Hope this provides enough information to get you started.

Clifton

Check the electrical connector under the steering wheel that connects the wiring harness to the light switch / hi-low bwam switch on the steering wheel. I had a problem where at first my lights would intermittantly turn off by themselves, then my headlights would not come on unless I pulled back on the high beam switch to "flash" the high beams. I traced the entire lighting circuit and had voltage everywhere, but found that I was losing the ground. I found that the electrical connector had actually melted "ahh..that was what that burning odor was!!!". The wires used for the ground, in my opinion, are not sufficent for the load and overheated. There have been several occurrences of unexplained fires under the dashes of these trucks, and I believe this to be the cause. I have complained to Toyota and the NHTSA about this with no results. If this is the cause you should definately take pictures and report this too, so that maybe something will be done about it before more vehicles catch on fire for no reason. The solution for me was to locate the ground wires and remove them from the connector, then use heavier guage wire to splice them back together. Hope this helps.