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Use an end wrench. It reaches over the insulating ridge of the relay and more easily carries the current. But he wouldn't get a click from the fender relay if the park/neutral/clutch safety didn't complete the circuit... This is why I asked if the starter turns when the solenoid on the starter is jumped. We eliminate the fender relay and the pink wire from the equation. Tom seems to have everything wired correctly.

Interesting that it's labeled C321 That is indeed the Duraspark II connector! Standard 698/ NAPA EC127 is the other side of that. But you're looking for the module side of it, and I don't think anyone (even Motorcraft in their pigtail catalog) ever sold a connector that got tossed with the dead module

Depending on how it was soldered on (this is all LONG before RoHS compliant lead free solder) it's best to flux first and then use Goot Wick or similar to pull the solder off the back of the board. There is no schematic for the millions (now Billions) of gates and junctions etched into silicon. If you did have all the masks you'd lose your mind, or die of old age before you figured it out. I often say that when reading even simple schematics like in the EVTM, that [solid state] is like having a map where the whole of Africa is labeled "thar be dragons here!" But some things can be deduced from what pins connect to what.

I got introduced to electronics by bread boarding Forrest Mims projects and desoldering the components on server rack sized boards from DEW Line radar stations. 👴 Gary is right. You need to work quickly and have a deft touch.

I honestly can't say. I wouldn't expect it is given that it would have to control twice as many channels. Do you have a schematic for the other radio? Is the chip the same number? Maybe Bill or Gary have something to offer??? I haven't dealt with this stuff in 40 years.

Not at the fender relay, at the starter. Of course out of gear and ignition off. But that's the point I'm trying to make (and understand)

Be careful with retarded ignition timing. Your engine is going to be running hot and 300's are known to warp heads and manifolds.

If the solenoid on the starter clicks when you jump from the black (hot) cable, either the starter winding isn't getting power (usually a braided connection) or the starter itself is dead.

Under the battery cable somewhere? I'm sorry i don't see it on my phone... Have you tried jumping the starter solenoid pink wire from the black hot lead, on the starter? If that works the pink wire is at fault.

Yup 300's ground the starter rather than the block like V-8's Where is the heavy black starter cable (not the bottom ground wire) going to? Battery +??? (because it should be)

I don't have a wiring diagram for the Super Duty trucks, but if it's similar to the 460 Hot Fuel Handling, then default for the switch valve is rear. Maybe that's why it's set up for the aft tank??? You can see in the drawing above how the flanges get wider at the cross members. I don't think 600/700 trucks are anywhere near the same chassis you have. Perhaps Gary knows if we have a member familiar with Louisville Assembly...

Three diamonds. 💎💎💎. Yes, I see the lead from just above capacitor 504 at pin 14 runs to the mic jack. The mic button comes before S4. So if neither the push button or the microphone button works, it's not the switch. Either the IC is bad or the leg of pin 14 is broken off. The XTAL OSC UNIT is the crystal oscillator that determines frequency. IC501 is the common thing that drives both the tuning and the display. Look closely at leg 14 (phones have macro cameras now) Is it broken or have a cold solder joint? If you could look at the package of the chip with a IR camera you might see a hot spot.

When I was six I could read resistors at a glance and bin them in my sleep. Now they're specks the size of coarse ground pepper surface mounted on multilayered boards. 'Times change'...

I think that 5-1 & 5-2 are actually two legs of a single DPDT switch that simply control whether each digit gets a solid ground connection or if it 'sees' 330ohm to ground. I don't think that's possible. IC 501 is controlling which segments of the display digits light up. It probably cycles through channels with a momentary switch, and outputs to the display on one side and the crystal oscillator on the other. (M) prefix makes me think Mitsubishi, but I don't have any of my semiconductor books to look up 58804B anymore. This schematic doesn't follow convention in switch symbols (buttons v/s toggles) but I suspect S4 as that's the only switch that doesn't seem maintained (arrow in lever) The channel select button on the left is momentary, correct?

Right. So you can ground the R/W wire to the block and check from the instrument plug to any ground in the cab, and the wire should be close to 0 ohms. You can plug it into the sender and it should read close to 73 ohms with a cold engine. You can check the sender itself from where the wire attaches and again see ~73 ohms (cold) If you get infinity (OL) with the first one there is a break in the wire. If you get (OL) with the second and third one the sender is bad or someone used Teflon tape and the sender is not making a good connection to the intake manifold. I don't include option three (cab isolated from ground) because apparently the oil pressure gauge seems to work.

With an iR camera you can see hotspots on the board. Some things (like a resistor that's sinking lots of current) are naturally going to be hot but if you see a hot spot inside an IC or some other component that's overheated it's a good clue there's a failure. Sometimes you can even feel it with the back of your hand. I haven't done much troubleshooting at the component level since I was a kid (about when these radios were made)

The link is a little clearer but I'm still zoomed WAY in and can only see a fragment at a time on my phone. S51 & S52 are the dimmers for each of the two digits (7 segment displays, FGABCDE) probably a DPDT* switch. S14 (to the right of Q501) would pull pin 16 of IC 105 to ground. I suspect this is what causes channel shift and the displays to change.

I'm trying to read this on my phone, but I would say what are the two switches directly above transistor Q501(?) on the left side? You say "one is a dimmer". What does it dim? The display? An indicator lamp? They both go to the IC header and switch between direct and through a resistor, it seems. (again, my eyes are not so good anymore and I'm looking at a sub6" screen) Circuit boards can definitely fail without scorches. IC's can fail internally, sometimes a resistor, transistor or diode will fail open without showing on the package. Often the best way to detect a fault without a logic probe is to look with an infrared camera.

I'm not saying "someone should piece it together" Just that other listings show the Motorcraft numbers. But i guess Motorcraft don't sell the shells or pins alone and Ford doesn't have listings for the pigtails.

Oh, that makes a lot more sense. I would say the listings for "Super Duty" are the commercial chassis trucks, since 'Superduty' wasn't a thing until the 1999 MY 250/350 pickups.

Too bad their listings don't include the appropriate Motorcraft pigtail, like a bunch of valves and switches/senders do.Should help Goose, and I'm thankful that you always go this extra mile for us, Gary.

Would probably be better to indicate resistance than voltage, as that's what the gauge is doing.

This is why I asked early on what the wheelbase is. I think when you get down to the last 1/3 of the chart and start seeing 137 & 161" WB (Super Duty) is where you find these commercial vehicles with the heavy narrow frame. I have to ask, is 'R' an incomplete vehicle opposed to an F-series with bed delete? I do see one mention -86/88 R (Super Cab)- and a couple "w/ all rubber fuel fill system" or "w/ plastic fuel fill system" Perhaps Haystack has: 80/ 250/350, F (Super Duty)-- E7TZ 9002-B Aft axle-plastic- 19gal, 20 gal. #E0TA 9104-CB, E8TA 9104-HA

I mean I like the novelty of repurposing an aircraft instrument for an off-road rig. Neither one really has any meaning for me but I find small pleasure in the incongruous (like having a hooded fire control button in the cab of a flatbed)

Would love to see an artificial horizon in Bob's Bronco.