Hello everyone. I am trying to wire up my aftermarket gauges on my 1985 Toyota's A-Piller mount. I have searched and found some information but nothing solid . I know that the lights use a floating ground. So if I hook up to the rheostat under the steering wheel my after markets will light up as my dash dims and vice versa. Never really being on at the same time. I have seen a few different places that I could hook up to the dash wiring and probably get it working that way and that's the route I would like to go. I have been looking through the 85 Toyota Pickup FSM and found this wiring diagram. From how I read it I should be able to tap to B-5 and B-6 for illumination. Does this look right to everyone else? Before people jump on this post just realize I do not want them to always be at the brightest and I don't want to have to put a resistor in line to my likeness. I also don't want to install another rheostat for this. Is there anyone out there that has been able to get it totally dimmable off the original dash dimming switch.

 

I have am referencing this two pictures from 85EastTxToy's post

 

I've never done it. My electrical wiring side says you have to go in parallel to the current lighting circuit to get "one effect or control" So B-5 and B-6 go to the current rheostat. one goes to the positive pole and the other to the center tap. This way all the lights see equal current. Now since you are adding "load" to the rheostat you should beef up the positive and negative feeds in some way. What I do not want to happen is the increased current draw overload the rheostat and over heat it. So "nebulously" I would get a slightly bigger rheostat and install larger wires and you should be good to go. Factory might be 20ga, I would move up to 14ga or so.
Toyota seems to use the minimum wire size it can get away with. I found out when I re-wired my headlights with 18ga for hot & grnd with a relay off the factory 20ga wires. Big improvement!