Confirmed it is a solid black wire that comes out of the main harness behind the cluster.

 

If it's truly a solid BLACK wire with no colored stripe for as long as you can follow it, then check continuity between the following:

1) Bare wire, and ICVR body (cluster plugged in)
2) Bare wire, and exposed metal behind the dash

This is a total of two resistance measurements. Report your results.

 

Do I do this with key on light switch on or both off?

 

Doesn't matter. But for grins, do it with the key OFF and the lights OFF.

 

I changed out my cluster and my dash lights work now. For some reason my fuel gauge goes to 3 quarters and stays there now. Fuel gauge worked fine before. Any ideas?

 

The last time we talked, your next steps were to perform some continuity checks to vet out the ICVR ground path and help ID a bare wire. Now you're saying you changed out the cluster instead? That's a lot of variables. You're going to have to fill me in on what happened between then and now.

FYI, it's not very efficient for me to suggest advice, then you come back 2 weeks later having done something completely different - and then ask me for input on a problem that arose from you diverging down a different path. You'll get this solved quicker if you just follow my instructions.

Where we are now, is that the original problem never got ID'd, there's presumably a bare wire that never got traced down, you've added a bunch of new stuff, and now I'm not really sure what you're working with. Please start from the top, describe exactly what is wrong (inaccurate gas gauge only?), describe exactly what was changed, and use clear and explicit detail. And most importantly, follow my instructions.

 

I changed the cluster because my circuit board was ripped/ torn and like I said half of the lights worked with ignition off, switch on. Buddy of mine gave me one. So I swapped it so all the lights worked to solve that issue. When I drove my truck home at night after swapping it all the dash lights worked. So I didnt think the bare wire mattered if they worked sorry. I can still do the test if you want.

Only issue im having now is inaccurate gas gauge readings. Everything else works. The gas gauge stays at 3 quarters of a tank even if tank is empty or full.

 

Yes, perform the two tests I described earlier.

 

Ok I will, I forgot to mention I put that solid black wire on a screw on the dash. Only way the lights would work. When I get time I will do your tests.

 

Please undo that connection temporarily prior to executing the test. The goal of the test is to identify the wire. I advise against tying a wire any which way until its source is understood. I've seen some bad dash fires doing it your way (and I mean bad). Please add this test with the wire disconnected as you found it:

3) ICVR body (cluster plugged in) and exposed metal behind the dash

 

Im going to do these tests saturday after I install my new gas tank and sender. Can you tell me how to do these step by step. Im bad when it comes to wiring, dont know how to use a multimeter properly. I also found another cut off black wire that comes out of the dash cluster connector.

 

78 ford guy:
Before you do anything like change the fuel tank, sender, etc listen to what FMC400 says about diagnosing. He has been helping me with a problem and I like you tried things out of order, or two things at once and made a complete mess of everything. Diagnose, diagnose, diagnose and don't just change parts. I speak from experience of being an idiot.

With wiring you don't want to take any chances. Loose wires can lead to big fires. The 70's Fords have been known to have significant dash fires when things aren't taped off or secured correctly. Get a multimeter if you don't have one. if you ren't sure how to use the multimeter, just ask.

Good luck and listen to FMC 400's advice!

 

Didnt have a choice on the gastank and sender mine had a huge hole in it. This truck is my means of transportation at the moment until I can weld my rangers block. Can someone explain how to do these tests for fmc with a multimeter?

 

Set your meter to read resistance, the units for which look like an upside-down horseshoe. The BLACK meter lead only has one place it can go; the RED meter lead usually has a couple places it can go, one of which should have the same upside-down horseshoe symbol (ohms, represented by the greek letter Omega).

If your meter does not auto-scale (and has a **** that says 2/20/200/etc...), start at "20", and make firm contact between each lead and one of the conductors under test. It does not matter which is RED or BLACK. If the meter reads "0", "1", or "INF", turn up to 200 and repeat until you get a real number. If you can never get a real number, it's called "open circuit." Report your results.

You're interested in checking the continuity between the instrument cluster voltage regulator ground, and actual ground (how easily can current return) which is done by measuring resistance. Measure the resistance between the ICVR body, and unpainted metal behind the dash. This is to tell you whether your dash cluster is grounded properly.

Next measure the resistance between the bare BLACK wires and unpainted metal behind the dash. This is to identify these wires. These tests are a hair different than what I described earlier because I'm trying to distill this into something simpler.

 

Test 1: icv regulator to bare metal was 72 ohms.

Test 2: wire 1 to bare metal was 0

Test 3: wire 2 to bare metal was -.016

Test 4: wire 1 to wire 2 was 72 ohms

All tests done with key off switch on. Did I do these right?