Your thoughts on this idea

[Skunksmash]

So now I'm down to the fuel. I got the tach and the new water temp gauge going good, but this new fuel gauge is giving me some trouble. My truck has two tanks, and that is making it difficult for me to just trace the correct wire all the way to the dash.

I need to locate the exact point I should solder to on the printed circuit. There are only 3 options, as I'm sure many of you are aware. The factory fuel gauge had only 3 plugs (or prongs) sticking out of the back. These 3 prongs just plug right into the little metal things that attach directly to the printed circuit itself. So I started out by just soldering the autometer contact points to the printed circuit. These trucks use 0 Ohms for an empty tank, and 90 Ohms for a full tank. For some reason the gauge must be reading far beyond that, cause the needle on it immediately dove down to way past the "Full" mark on the gauge. And stays there even once the whole thing is installed back into the truck.

So am I doing something wrong here? Is there some reason that soldering this won't work? Maybe I am creating too much resistance by soldering? I don't want to just keep guessing and soldering and then desoldering, cause I don't want to ruin my precious printed circuit. I need to get this right the first time. Well, the second time I mean. I can't just keep trying things.

[SAATR]

I would have suggested first running test leads to the gauge from the traces you intended to use to make sure the gauge functioned properly.  I would say you probably have the wires backward, as a good solder joint will have negligible resistance, and you are simply applying voltage and ground to the wrong poles of the gauge.

[Skunksmash]

That is a good idea. See I knew I just needed some new clear head to help me think about this.

[Skunksmash]

Ok here is where I am now. Finally got more time to work on this project. It just sits there for months at a time sometimes lol. Anyway, I got everything all figured out with the gauges except one last detail. I took some pics to show you what I'm talking about. If you look at the pic of the factory plug, that plugs into the gauge cluster itself, you can see that each little "pin" is numbered on each side. With use of a Chilton's manual, I have narrowed the sending unit wire down to either the number 18 pin, or the number 16 pin. Gotta be one of those two. One the page it says that its pink. Yet both are pink, but one has a stripe.

I highlighted on there to make it easier to find.

[Captkaos]

If you have dual tanks, the wiring is routed to the tank switch.  the one coming straight out of the harness runs to the back and terminates.  The one from the switch plugs into the one on the harness and runs down to the switch connector and then to each tank.  Both of these wires go to the cluster, they are the tan/white on the bulkhead connector.   Somehow the switch to pink in the #18 slot.   If you are tying into the Pink #18, it should work.

Did your fuel gauge work before?

[Skunksmash]

Yeah it worked before, although poorly in my opinion. The new one doesn't seem to have that wavy needle problem that got on my nerves. Guess I'm just a perfectionist or something. But I did get the new fuel gauge going finally. It is the number 18 slot. All you really have to do is trace that slot on the printed circuit, to find your solder point. It turns out its the far left hole. The other two are just positive and ground. Thanks for all the help.

Now I just gotta get the tach going and I'll be ready to put the truck back together. As you can see from wiring diagram pic, the wire for the tach is white. Unfortunately, there are two white wires on the coil. One on the left, and one on the right. This is probly a dumb question but, shouldn't I just be able to use my Digital multimeter to figure out which side is negative and which is positive? Only get once chance at this one. Get it wrong and ruin the tach.

[Skunksmash]

Well now the dang tach has started giving me trouble. So to troubleshoot, can I just pop the hood, hook up the negative on the tach to the negative on the battery, the positive on the tach to the positive on the battery, and the signal wire to the negative on the coil? I'd like to test with the simplest configuration possible, so I can then rule out what is wrong. I'd like to just do it all right there under the hood. Is there any reason I shouldn't do this?

[VileZambonie]

Did I read this right? You are soldering your connections to the printed circuit? You should be going directly from the harness to your new gauge not the printed circuit.

http://forum.73-87chevytrucks.com/smforum/index.php/topic,9072.0.html

[Skunksmash]

Yeah. I am soldering directly to the printed circuit. I guess I didn't do it exactly right, but it was quick, easy, and it worked. And I gotta stop trusting the guy doing my soldering lol. He had the positive and negative reversed on the tach. Same thing he did on the fuel gauge to begin with. I suck at soldering, and he's very good at it. Just not so good at hooking up the connections to the right points heh.

[bake74]

Yeah. I am soldering directly to the printed circuit. I guess I didn't do it exactly right, but it was quick, easy, and it worked. And I gotta stop trusting the guy doing my soldering lol. He had the positive and negative reversed on the tach. Same thing he did on the fuel gauge to begin with. I suck at soldering, and he's very good at it. Just not so good at hooking up the connections to the right points heh.

     Maybe you could supervise more and look over his shoulder and just make sure he does it right, then you can the best of both worlds.

[VileZambonie]

Why would you solder your connections to the printed circuit instead of going directly to the wiring harness?

[Skunksmash]

Well the way I look at it, why not? Its all right there and I don't have to run all this wire and make all these connections when all you have to do is pull the gauge housing, and go to town soldering. Then simply plug it back up and it all works. Well, if you don't have your pos and neg reversed of course. I didn't have to cut into loom on the harness, or otherwise come up with some way to splice into those wires. I wanted to leave the harness alone if I could, and just plug it in and have it work.

I think I had this idea that I wanted to just alter the factory gauge cluster to be what I wanted it to be.

[Skunksmash]

On an 87 it will be labelled ING

Ok I used up the ING on the fuse box that already had a fuse in it. I just got one of those adapters with a wire on it that lets you plug in two fuses. You get 2 fuse slots in the adapter. 1 for the original fuse that was already in the ING fuse slot, and one for the new fuse that you want to add.

So now I need to make use of that extra ING slot. But how can I do it? There is a piece of plastic made into the middle of the slot, that won't let you plug in a fuse. Its like there are two smaller holes for the extra ING slot. What goes in there?

[jaredts]

Would it be easier to just tap into the circuit that you already added using the fuse adapter?  I think a spade connector goes into the slot you are talking about.

[Skunksmash]

How would you go about that?