I'm installing a boost and temp gauge and I have a question.. when wiring into the ash tray wiring, I read that the illumination wire must be split and connected to each wire going to the ash tray... now is it alright to wire another 2 to 1 wire for a 2nd gauge? Seeing how the gauges only use <1 amp , I just want to make sure..

 

No, do not ground the other end of the lamp. The RX-7 instrument lighting system is a pulse width modulated system (to control the brightness). The instrument lamps are supplied with 12 V on one side and the control grounds the other side of the lights for some fraction of time. You need to isolate the gauges so you don't ground either side of the lamp. Then you wire each side to the ashtray lamp wires. If you do it any other way, you will not have dimmable lamps. If that is not a concern, measure each of the ashtray lamp wires with a voltmeter - one will be a constant 12V, the other will be less. Use the 12V to power your gauge lamps. So, find the wire that is 12V, connect it to both gauges lamps "hot" side. The other side of the lamps (this may be the gauge case) either goes to the other ashtray lamp wire (without grounding the new gauges), or it goes to ground and not to the ashtray lamp wire. If you have a plastic gauge pod, having a dimmable boost gauge is easy, but the temp gauge may be a problem, as it may need to be grounded as the sensor may be referenced to ground.

I hope I was clear enough. If not, let me know.

 

Splice one wire to each of the ash tray wires. Make each wire long enough to go to your gauges. Somewhere near the gauges, splice another wire into each of the original wires. You will now have two wires connected to each side of the ashtray wires. Now you simply connect one wire from each side of the ashtray wires to each side of your gauge lights.

This will give you dimable illumination for both gauges, with the factory dimmer.

 

Wire it like this dude, this is how I did mine, works a charm. You don't have to worry about polarity because if your gauge uses a standard lamp, the lamp will work connected both ways. Just don't short out the ashtray wires and you'll be set.


That said, if I was doing it again, I'd not bother with the dimmer. It's cool to be able to dim the gauges with the dash lights, but I NEVER dim the dash lights! So I probably would have been better just using the same 12V I used to power the gauges. Might have been a bit brighter....