280z Dash Dimmer repair/issues

[NC280z]

Good evening all,

 

    While I'm sure this should be posted in the electrical section, it seems more people watch the GT section so I'll post my issue here.

 

I'm tracing an issue in the dash wiring that's keeping me from having any gauge illumination lights. My dome lamp, map lamp, etc. all work, but the gauge illum lights only come on extremely dim, in ones and twos, or not at all. I've moved the dimmer knob back and forth, and found that when the gauge lights do come on, they only come on briefly before the fuse glows red-hot and burns out. When the dimmer is moved to the brightest setting, the dash ammeter also dips a great deal, as if the dimmer is putting a large draw on the electrical system. I took an ohmmeter to the rheostat, and it goes from 0 ohms to several mega ohms in a short turn. FSM says 10-0 ohms, so I'm certain that this is the problem.

 

That being said, I can't find any remanufactured dimmers, so I'm going to try and repair it myself. If I can't fix it, I'll put a 5 ohm resistor in its place (middle ground between factory 10-0 rating), but I don't know what the wattage should be. Anyone have a good guess as to what wattage rating I should replace the dimmer with?   

[datzenmike]

The wattage would have to be equal to every bulb in the illumination circuit. They are mostly 5-9 watt each. Take a look at the rheostat... is probably ceramic, which will tell you how hot it gets.

 

Later dimmers are not of the resister kind but solid state, but use three wires, and do not get hot..

 

[NC280z]

I'm hoping that it's just a corroded or dirty connection somewhere inside the pot's canister. Since it's one of the older styles, it shouldn't be too hard to pull apart and clean. The pic of the one you posted looks like a ZX dimmer, but I've read that there were different styles for 240's, 260/280 and 77-78 280's.

[datzenmike]

This one is from a 720 or S110 200sx maybe a Maxima perhaps. The '78 and up 620 had them so maybe this was the cut off year for the old style. Either way the dash lights are never bright enough in the 620s. The dimmer switch should go as high as Nigel's amp.

[NC280z]

So I think I have a short elsewhere in the circuit. I pulled apart the dimmer, and found that one of the rheostat's coils was burned up. I repaired it, placed it back under the dash and as soon as I put the lights on the dimmer burned up again. I turned it to the max setting, and same issue with the fuse blowing like yesterday. I decided to just jump the connection, leaving the dimmer out of the circuit and the wires got hot, quick.

 

I pulled the fuse box out, and found that one of the previous owners had burned up the aircon fuse pretty badly, and decided to do a complete hackjob and wire not one, but TWO 20 amp blade fuses in parallel, and then "splice" (if you can call it that) these two fuses into the white w/ red stripe wire that runs into the box. Very poorly done job, so who's to say there isn't more to be found hiding under the dash. I just hope I can find this issue easily, because pulling the dash out is my worst nightmare.

[NC280z]

Did more troubleshooting today, and found something strange. With the combination switch connected to the rest of the wiring harness, I have continuity between the switches green/white wire, and the switches white/red and solid red wire. Continuity is something along the lines of a few Kohms, and all three wires have continuity to the switches metal frame. 

 

When I disconnect the harness, there's no continuity between any of the switches wires or to the switches body. I found that testing at the harness shows that something's amiss, especially since the 20A fuse for the lights is pulled and I still get continuity. I used a test light and found that I don't have a short, but what could still be causing me to blow fuses when I try to turn on the dash lights?