gauge ground question

[LargerCharger383]

ok I have a 74 with rallye gauges.  I just re-wired the entire car with all year one harne$$e$.  Everything works perfect...except my gauges.  None of the electric gauges work and the gauge lights are on all the time, regardless of whether the head/marker lights are on.  They only turn off when you press the brake pedal.  I looked at the ground wires and the only thing that looks wrong is that there's a ground relay or something towards the right side of the back of the cluster, around the voltmeter, and the far left prong has no wire going to it.  any ideas?

(tried attaching pictures but they were too big and I don't know how to resize them on a mac, I'll try tomorrow.)

[buie1289]

LargerCharger, can you e-mail those pics to me? I think I can help you out with this.

[LargerCharger383]

email sent

[buie1289]

OK, got the pics. Give me a couple of minutes to mark on them and I'll show you where everything goes. Funny, I just got finished wiring all this stuff last night.

[LargerCharger383]

sounds great man, thanks a lot

[buie1289]

OK, so here's the deal. The silver relay you're talking about is actually the Instrument Voltage Regulator (IVR). Basically, this things whole purpose in life is to take +12Volts DC in and step it down to +5 Volts DC because your fuel gauge and your oil press. gauge both require +5 Volts DC to operate. Basically, my response here will get you all squared away with your gauges (provided your IVR is good) but I'll need some more info to assist with the dash light issue. Also, one thing I should mention about the IVR. If you've ever seen the inside of one of these things, you'll be amazed that they work. They're just a small set of points that open and close from the heat generated by shorting 2 contacts. If you still have your AM radio, then there's a good chance it clicks through the speaker because of these 2 contacts opening and closing about twice per second. With all that being said, these things tend to fail, when they do the points will either seize open, which means Fuel and Oil Press. gauges stop working, or they will seize closed, which means that both gauges will burn up and send you hunting for replacement gauges.This thing can be eliminated pretty easily for about 6 bucks. I can provide instructions if you're interested. Anyways, on with the pics.

[buie1289]

Also, here's your dash pic, with some markup showing where wires go.

[71_deputy]

never seen the clock power coming from the VR

The Vr only has power when the ign. is on.

Clock need power all time to work.

[LargerCharger383]

isn't that a power harness going to all the guages?  The one wire is just red cause it's got shrink tubing on it.  But that makes sense, I'll hook up a wire from the fuse block.  Do you think that'll help with the lights?  Also, I don't have a clock.  I have speedo, fuel, oil pressure, volts, and temp.  It's a rallye cluster.  thanks for the help though, I'll hook a power lead up and see what happens.

[LargerCharger383]

also, do you know where I can get an IVR from?  might as well throw one in as long I'm doing everything else.

[buie1289]

71_deputy, you are right. I don't know why I didn't think of that Also I can't imagine why mine was like that. Guess I would have noticed that being a problem when I get a clock that actually works.

[buie1289]

LargerCharger, I don't think that will help with the lights as they come off the fuse box from a constant fed circuit, whereas your IVR is fed from a switched circuit. When I get home tonight I'll look at my fuse box and tell you which one feeds my dash lights. I think it's on the left side either the 2nd or 3rd one up from the bottom. Just a couple of things to check, though would be the ground for the dash lights. On a stock harness, it is in the vicinity of the headlight switch, if it's not grounded, then the lights won't work (I had that problem). Also, as I was tracing out wires, here's what I noticed: If I remember right, there is a wire that comes off the fuse box on the constant side (I think it's pink) that runs up to the headlight switch and supplies constant power to one of the terminals for inst lamps (maybe more), that wire leaves the switch on another terminal (tan wire, I think) and returns to another fuse on the fuse block. It then leaves the fuse block on an orange wire and from there feeds your dash lamps. If it were troubleshooting this, I would start by checking for +12V at the pink wire on the headlamp switch, then I would turn on the headlamp switch and check for +12V on the switch at the tan wire, next check for +12V at the fuse block on the tan wire where it enters, next check for +12V at the orange side of the fuse block, then check for +12V at one of the actual bulb sockets. I think in checking all this, you should run across your problem. I'll put up another post in a second covering your last post.

[buie1289]

On the IVR, they're available at most any decent parts house out there. My local NAPA has them for arount $25.00. If it were me though, I would not go back with that style regulator. I just converted mine over to a solid state chip, using a Texas Instruments 7805 voltage regulator ($1.59 @ Radio Shack) and a generic TO-220 heat sink ($1.49 @ Radio Shack). Using those 2 parts, about 8 inches of wire, a little solder and some hot glue, mine is fixed for good. I've done this to my '64 Barracuda and to my old non-Rally dash in the Charger as well as 5 or 6 for other people. It's cheap, easy and we don't run the risk of smoking our gauges since the solid state chip has fault protection built in.