VAhunter

Here's what i want to do on my '93 pickup, run 2 driving lights on the brush guard to come on with high beams, i know i need a relay somewhere but i dont know how to wire them into the high beam switch. I also want to run a light bar above/behind the cab with 4 lights, most relays so not to use more than 2 lights per circuit, but can you put them on the same switch?

RAD4Runner

Depends on how you''d like to wire your control, but I recommend that you stay consistent with Toyota's switched-ground wiring scheme. This means you open or close the ground , rather than switching positive V to control circuit- that's the power to the coil of the relay. This is safer because you minimize length of wires carrying +12V, and limit the +12V runs to between stock lights, aux lights, relay and battery. You only run wire from ground side of relay to dash, to switch, then to ground point at driver side A-pillar. If insulation on that ground wire wears out for any reason, chances are you'd be shorting to ground. Worst-case scenario? Aux light comes on. No blown fuses.

To make aux lights turn on ONLY when high beams are on:
Edit: Sorry.... Need to provide more details for turning on ONLY IF High beam is on

However, to make aux lights turn only when tail lights are on:


Example of tap from right-side marker light (first-gen Runner) is ALL-green wire below.

For high-beam tap, pls check your model's schematic.

OK to control more than one relay with one switch, IF you promise that you only use the switch to control power/round for relay coil through the switch.

VAhunter

Actually i was rethinking the overcab light layout, maybe have 2 long range lights and 2 floods on separate switches

RAD4Runner

Same concept, depends on which stock light switch you want to also control your aux lights. Turns out Aux lights on with with high beams would be be slightly more complex than aux on with tails OR with ignition. Would help if you posted schematic for your model truck so we can help.

VAhunter

I just want the driving lights to come on when I flip the switch for the high beams and go off when the high beams go off so they'd be wired to that switch. The overcab auxiliary lights will be on independent switches on the dash somewhere...may just put a switch plate in the ash tray slot

4Crawler

iTrader: (3)

Pretty easy to do, you have two sides of the relay coil, one is the power side and the other is ground (85 and 86 terminals). Since the Toyota headlights are switched ground (high beam wire is grounded to turn on the high beams), all you need to do is hook one side of the relay coil to the high beam headlight wire and hook the other side to say the headlight common terminal (that side has power when the headlight switch is turned on):
- http://www.4crawler.com/4x4/CheapTri...l#HarnessTypes

So basically you have your relay coil wired in parallel with the high beam bulb filament. Then if you want a switch in there to disable those aux. lights, add a switch in-line with the relay, open the switch = no aux. lights, close the switch and they run with the high beams.

The trick is you need to account for the switched ground wiring on the headlights. You have 12 volts at the common terminal and then ground at either the low or high beam terminal to make that part of the bulb light. Because of that, you don't want to introduce any other ground or power connection into the relay coil circuit. So only use the headlight voltage and ground wires.

RAD4Runner

Thanks, 4Crawler! Upon closer look at the headlight circuit, I realized that:

• Altho the headlight relays control the +12Volts to the headlights, the combination/dimmer switch still carries the full headlight current (approx 10amps!) on the ground side, and
• You are right; path of load current is convoluted - It runs from battery, back to dash, to light switch, back to engine comp to headlights.

Similar to the starter system wiring flaw. Goodness! Where did those Toyota engineers learn how to use a relay in a circuit?! On the brighter side, these are proof that Toyota parts are built tough

Tonight my Christmas project priorities just changed to Upgrade (wire thickness) and Modify headlight circuit, as follows:

• Insert relay contacts between headlight gnd and actual ground. Then,
• Combo/dimmer switch pins 5 (R-Y) and 6 (R-G) will switch ground to relay coils

Advantages:

• Contacts will carry head light current to relieve combo/dimmer switch, and
• Load-carrying wires will only run from battery to relay to headlights.

Will post details to my build thread. Shopping time this weekend.

4Crawler

iTrader: (3)

My guess is that Toyotas seem to be designed with safety as an overriding factor, above reliability or ease of service/modification. Like the starter wiring is set up so that even if the starter relay sticks on, you can simply turn the key off to kill power to the starter. Of course the solenoid can still stick on, so not foolproof. Same with the headlights, horn, radio, gauges and many other circuits. Those items are floating in that they are not hard grounded. So if part of the circuit does get grounded usually nothing bad happens. Like if the low beam headlight wire is accidentally grounded, the low beams come on, no fuse blows, no wires burn up. In a switched power system, same thing happens and you blow the headlight fuse or burn up the relay or wiring.

But this switched ground stuff makes working on the vehicle difficult, like if you want to add a gauge or radio or other lights, you might have trouble if that device has any case grounds. For example a gauge with a back light usually has the case grounded, then only one terminal for the light and one for the gauge power and one for the signal. If you try to hook that gauge to the dimmer, it'll mess everything up on your dash sine all those backlights are floating grounds. So if you want to tie into the switched ground wiring, you need to follow the rules for every connection. The other option is to totally bypass all the Toyota wiring and come right off the battery and don't tap into any Toyota circuits and run everything you add in switched power mode. Or if you need to tap into a Toyota circuit, only use that to energize a relay coil then you can do whatever you want with the relay contacts.

RAD4Runner

Thanks, 4Crawler.

Agree with safety concern. In fact, when I did my cranking circuit mod, I added a kill switch to interrupt power to starter solenoid.

Agree. There's a built-in back-up on headlight circuit because light switch (stalk) needs to be on before headlight relay sends power to positive (common terminal?) side of bulbs. My plan is to switch high and low beam grounds with relay contacts (mounted near fuse box). This way current-carrying ground wires run only between bulbs and directly to battery negative (on fender ground here). Instead of running into the cabin to dash, and back to fender ground.

I just want to hard-wire my mod. However, I believe your harness mod does same- shorten current path, correct?

Yep, stalk switch high beam terminal 5 will switch relay coil ground. Normally-open contacts will switch high beam ground, normally-closed contact will switch low beam ground.

I'll submit my schematic plan to forum for review just in case I miss anything
Regards,
RAD