where is the ground coming in?

Puttings relays in for a tow harness, totally stumped. What do you think?

The defeat switch will break the circuit. How are the 85's supposedly grounded? (I suspect some grounding misunderstanding.) If any of the +triggers are grounded when not +12V (for relay on/energised) - is there are reason or necessity? But even if one +trigger is grounded, the other relays will only get a maximum of ~6V (ie, half of whatever your system voltage is) which may not be enough to energise them. If 2 are grounded, then the remaining relay will see 2/3rds of the system voltage (8V - 9.6V) which may be enough to energise it.

unplug the relays and test the trigger wire teminals on the sockets ... you will see that you are grounding backwards through all of the trucks bulb filiments.

install diodes on each of the trigger wires and the problem will go away.

yuk

quiet rural missouri, near KC.

If your system moves you physically and not emotionally, you have wasted your money.

... and that's the +trigger to ground I referred to. (D'oh! I'm curious as to why the defeat switch. If the trailer is attached, the lights should mimic the vehicle's. (And if not attached, the plug/circuit is disconnected.)

maybe the drivers behind him dont like all that clicking noise in heavy traffic without a trailer.yuk

quiet rural missouri, near KC.

If your system moves you physically and not emotionally, you have wasted your money.

Soft subs eh? Then insert a diode in each (or at least 2) of the 85 to switch paths (line to switch/GND).

I had the same thought about the triggers resting at ground but they don't test that way, there's no voltage at rest. Might try diode-isolating the triggers but I'm going to break out the individual connectors on one relay harness & apply them one at a time to see which terminal is the source of B- first. The relay clicking noise is annoying, I'd like to defeat it when not in use - hence the switch. This was an after thought, didn't think it'd be as loud as it is.

85's are summed & feed into a simple SP switch (currently unmounted). From the switch they connect to vehicle frame. The problem still happens even with the frame connection unscrewed. It's a ghost-ground! I wondered if the relay bodies were grounding thru the mount screws that attach them to the truck body but they're nylon, there's no way.

when you parallel that many bulbs upstream, current is gonna backflow.

im pretty sure diode isolating all of the 85 terminals or all of the 86 terminals is the easiesy way to remedy the problem without revamping the whole system.

i wonder if it is so bad that when you sit in total darkeness and hit the brake, the dash lights might light a bit.

PLUS... how do you have a single relay controlling both blinkers?

yuk

quiet rural missouri, near KC.

If your system moves you physically and not emotionally, you have wasted your money.

Actually 4 relays, 2 for blinkers. But then removed one since the brake & blinkers are the same. So now it's 2 for blinkers & 1 for running lights, no brake relay. Good eye tho. Now, someone teach me how to twist multiple wires together in that perfect symmetry some people manage to do...gonna start a new thread on that.