4Runner Alternating Headlights

im all set to hook it up but i have a quick question b4 i do.  wont both lights go on everytime the relay clicks, because the voltage will go back through the wire to the other bulb right?

How are you hooking it up?

i was going to hook each lead up to the wire/plug right at the bulb

Yes you have to isolate each one first before you can make them alternate. Use relays and not diodes to isolate them since you'd be losing .7v per light through a diode.

You can make this with a flasher, 2 relays, a switch, and a fuse holder. Wire as follows: Power through the fuse to one side on the switch. From the switch run to the flasher, and to 30 of one relay. The output out the flasher will run to 85 of the relay. Ground 86 on the relay. Connect one headlight wire to 87, and the other to 87a. This will allow the the flasher to alternate the relay. I would do this on the bright side. If you have seperate circuits for right and left head light, your done, if not install another relay as follows: While making the connection to one of the headlight wires, install a relay BEFORE the connection like this: 85 and 30 from the headlight switch. 86 to ground 87 to the wire going to the headlight. 87a unused. Your normal headlights will now work, and so will your wigwags. OR, instead of the second relay, you could use a diode in forward bias on the wires running to the headlights before you connection from the first relay. How did I do guys? Mark

Diode isolation is fine. it will take .5 to .7 volts to "turn it on", but once on I don't belive you will see a voltage drop across it.

Be warned! Not using competently designed and built flasher units can cause damage to your vehicle by burning out the headlight control computer. Better to spend $38.00 on emergency vehicle quality flasher unit than hours of troubleshooting and expense. Just an FYI from someone who installs them for a living. Good luck.R Jackson

Owner/Installer

TRM Emergency Vehicles

Information is advice only and should be confirmed with OEM or quality test equipment.

Boyertown, Pennsylvania

I agree that this would be a better option. Do they isolate the circuit from the headlight switch?

yes they isolate it. you need to hook up usually 7 wires. -constant 12volt -switched 12volt -ground - to driver headlamp -from driver headlamp -to pass. headlamp -from pass headlamp There is also a kill wire you can hook up to diasable it when the parking lights are on but I never use it. And several pattern choices using jumper leads.R Jackson

Owner/Installer

TRM Emergency Vehicles

Information is advice only and should be confirmed with OEM or quality test equipment.

Boyertown, Pennsylvania

But how do you know if the vehicle has a headlight control computer? Say for a 92 Cherokee? or 95 Taurus? Is this something that started around a particular timeframe or do you have to just go one by one?