67-72 Electric speedo

[ewoody625]

Originally Posted by ls1nova71

I'm not sure what that wire labeled ammeter is, but I probably wouldn't use that for ignition power. The gauges will have power already going to them, so you would just need to use that wire. The speedometer wire would come from the PCM.

I rewired the whole truck with a painless harness and the ammeter to ignition was one of the wires in the stock cluster plug. I cut that off and spliced in my connector for the updated gauges. So the green wire from the speedo I need to wire to whatever it is out of the pcm?

[ls1nova71]

The speedo out put from the PCM will be pin 50, a dark green with white stripe in the C2 connector, which is either the red or green one depending on what year your engine is.

[ewoody625]

Originally Posted by ls1nova71

The speedo out put from the PCM will be pin 50, a dark green with white stripe in the C2 connector, which is either the red or green one depending on what year your engine is.

Thanks

[ewoody625]

So I guess I don't have this down yet. I got the speedo hooked up to the ecm but I'm not sure of the ignition source. I have a wire from the truck labeled gauges B+, which leads me to believe that's hot all the time? I don't want power to the gauges all the time do I? The other wire I have is the one labeled ammeter to ign sw, which I'm guessing is ignition switch. Do I need 2 ignition sources? One for the speedo one for the other gauges?

[ewoody625]

I just took a test light to those wires. Gauges b+ is hot key on, ammeter to ignition switch is constant hot and I have a wire labeled ammeter to fuse block which is constant hot. I'm lost...

[ewoody625]

I studied your picture, I think I have this figured out. I see you have all the ignition wires coming off the fuel gauge and I'm thinking the wire i need is the gauges b+ since it's only hot keyed on.

[ls1nova71]

Yes, you only need one key on hot wire to go to all the gauges. Are you trying to hook up the factory ammeter?

[ewoody625]

Originally Posted by ls1nova71

Yes, you only need one key on hot wire to go to all the gauges. Are you trying to hook up the factory ammeter?

No I did the square body voltage gauge swap. Those are just the wires I have in the truck harness. I'm not sure why those ammeter wires are constant hot and the gauges b+ is not. I'm gonna use the gauges b+ wire and just leave the others alone. Thanks for all your help I think, i hope i have this figured out. Thanks again

[ewoody625]

I plugged in my gauges the other day and as soon as I turned the key the the fuse blew. My dash lights and turn signals are working so I assume my grounds are good. I hooked up each gauge one by one and when I got to the volt gauge I swapped from the square body the fuse blew again. Do I have a bad gauge or is it something else? Thanks in advance for any help.

[ls1nova71]

Can you post a pic of how you have it wired? My guess is it isnt wired quite right.

[ewoody625]

Originally Posted by ls1nova71

Can you post a pic of how you have it wired? My guess is it isnt wired quite right.

I will try to get a picture later today.

[ewoody625]

Here it is

[ls1nova71]

Well, I cant really tell from the pic, but I would make sure the voltmeter isnt grounding out on the tin.

[ewoody625]

Originally Posted by ls1nova71

Well, I cant really tell from the pic, but I would make sure the voltmeter isnt grounding out on the tin.

I ran all my grounds to the screw just above where the factory plug plugs in. Then I grounded my plug just to the right of that. My lights are working so those should be fine right? Are you saying check that the gauge itself isn't grounding out in its mounting?

[ls1nova71]

Yes, make sure the mounting bolts are not touching the tin. There are little plastic parts that insulate them, make sure they are there.

[ewoody625]

Originally Posted by ls1nova71

Yes, make sure the mounting bolts are not touching the tin. There are little plastic parts that insulate them, make sure they are there.

Great I'll check that out. Thanks so much

[ewoody625]

So that was the issue, fixed that but none of the gauges work. Lights are still good, except ses light. I'm ready to throw in the towel....

[ls1nova71]

Did you fix the fuse that blew? If you have power to the gauges I would think that at least one would work, highly unlikely that they are all bad.

[ewoody625]

Originally Posted by ls1nova71

Did you fix the fuse that blew? If you have power to the gauges I would think that at least one would work, highly unlikely that they are all bad.

Yes I did, it was grounding itself out. The only needle that moves is the gas gauge but it goes to empty when I turn the key on and the tank is not empty. The volt gauge doesn't register anything. I cant keep it running long enough to see if the temp gauge works. And I have no idea when I'll be able to test the speedo. My check engine light doesn't come on when the key is on too.

[Factory Guy]

ls1nova71 pm sent!

[chev-obsession]

Finally got this speedo completed! After reading through this thread about 100 times no exaggeration, and asking tons questions I have it completed! A couple things I did a little different was powder coating the tins since I have the equipment and cutting a hole for the tach and clock and welding a trim ring to keep the factory look.

I haven’t put the ls engine in my truck yet and I’m going to wait until the engine is in to install the new cluster. To check my work before installing, I unplugged the factory plug from the cluster that is in the truck now and used alligator clips to connect from various pins in the factory plug to the lights and gauges in the new cluster. The only thing that I haven’t tried is the speedo which is most important. So super excited to try it out. Thanks to Eric and Tom for answering all of my novice questions! I was disappointed in my painting skills, a couple of the numbers didn’t turn out the best, I should have took the decal off sooner. This project defiantly tested my patience!

[chev-obsession]

Another helpful thing I found was this diagram of the color of wires in the factory plug. Also a pic of the cluster light up with LED bulbs

[DM72C20]

Just checking in if anyone has this swap working with a Gen IV engine? I've got an 09 4.8 going into my 72 C20 and was contemplating this gauge swap, but saw that it might not work. Thanks from social distancing in Toronto.

[ls1nova71]

Originally Posted by DM72C20

Just checking in if anyone has this swap working with a Gen IV engine? I've got an 09 4.8 going into my 72 C20 and was contemplating this gauge swap, but saw that it might not work. Thanks from social distancing in Toronto.

I have not personally messed with a lot of GenIV engines, other than one L99, but from what I have read, they don't have a dedicated speed signal going to the instrument cluster as its all on the CAN bus. When I did the L99 harness I believe there was a place to add a wire for a speedo but you needed to have it programmed to work, which we didn't do. So unless you can figure out that way to get that signal out of the ECM, then I am going to guess that this wont work for you.

[aknovaman]

Not directly a solution but good info none the less.


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