Blowing fuses (no dash lights)

[s30zgt]

Hello

 

I recently reinstalled my dash and harness. I turned the car on and flipped the lights on. Headlight, tail lights, turn signals and side markers all worked but my dash had no light. When i turned the dimmer (rheostat) to high i heard what sounded like a sizzle and saw a puff of smoke through the dash. I immediately turned the car off and checked where the smoke had been coming from. Turned out that the rheostat had fried. Thinking it was just a bad rheostat, i read that it can be bypassed so i connected the wires together and turned the lights back on. This time the Park Tail fuse popped and once again i turned the car off.

 

I went back over the wiring diagram, making sure no connection was loose or corroded on the dash harness. I also searched the web and took care of all the known issues like the turn signal grounding improperly and corroded side markers hoping that would take care of the issue. Once again the Park Tail fuse popped. 

 

Then i tried to isolate the problem by disconnecting all the exterior lighting (head,tail, turn, side markers and inspection light). This time when i turned the lights on it popped the fusible link on the starter. The previous owner swapped it out for one that uses 30a ATO fuses.

 

I have a friend bringing a voltmeter this weekend to help find out where our problem lies but I want to know if you guys see any glaring issues that pop out at you? Could it be the voltage regulator? Maybe a bad ammeter?

 

Any help would be appreciated.

 

Thank you.

 

oh and this is the lighting diagram im using in addition to the FSM diag.

http://www.atlanticz.ca/zclub/techtips/wiringdiagrams/240z/1971_240z.gif

[Domzs]

Whatever you did to by-pass the dimmer ( rheostat ) , undo it and install new fuse ( preffered ckt breaker ) and recheck . From what i read , the fuse was ok until you by-passed the dimmer switch . You might have illumination wire pitched somewhere , don't think exterior lights are the cause .

[Zinpieces]

Here is a trick that I have been using for years and years. Works in cars and buildings. Replace the fuse with an automotive lamp. Take a 1157 in a socket with a pair of alligator clips or spade connectors and put it in place of the fuse. Even with a direct short circuit the current flow will be limited to the draw of the lamp. A bright lamp means a short circuit. As you look through the car and move things around the bulb may suddenly either go out or dim considerably. That's when you've located the problem! Hope this helps.

[Domzs]

Here is a trick that I have been using for years and years. Works in cars and buildings. Replace the fuse with an automotive lamp. Take a 1157 in a socket with a pair of alligator clips or spade connectors and put it in place of the fuse. Even with a direct short circuit the current flow will be limited to the draw of the lamp. A bright lamp means a short circuit. As you look through the car and move things around the bulb may suddenly either go out or dim considerably. That's when you've located the problem! Hope this helps.

Good trick , I forgot about that .

[s30zgt]

Thanks guys for the suggestions.

 

Domzs, the bypass was to simply plug the wires that go into the dimmer into each other. Those wires have to pass power through each other, either directly or through the rheostat, in order to power the lights on the gauges according to the wiring diagram. With those wire disconnected i have no other issues with any other lighting or fuses popping.

 

That is a good trick Zinpieces. i will have to try that. We are talking minimal damage since the power is running through the lamp right? it was popping that 20a Parktail fuse in seconds.

 

Just so i have this clear. According to the diagram on the fsm, power from the alternator flows (WR wire) through that 20a ParkTail fuse through the (GL wire) to the combination switch, then is bridged by turning the light switch to the 1 or 2 position, then flows on the (GW wire) to the rheostat (RL wire) to send power to the illumination lights on the gauges. Is this correct?

 

And if so, wouldnt the issue be after the rheostat along the (RL wire)? Is it possible that the power is grounding around there and pulling more power through the  Parktail fuse and causing it to blow?

 

Thanks again for all the help.

[Domzs]

Like i said , no reason to check your exterior light ckt. . Concentrate on illumination side of the ckt. , from rheostat to illumination .

[s30zgt]

ah my mistake.

 

i will check that end of the harness and make sure nothing is grounding improperly.

[HowlerMonkey]

About 70% of the times I have seen this, it is after a stereo installation in which one of the OEM wires providing lighting to the original stereo or panel lighting nearby is shorted to ground.