As some of you know, I've been thinking about going with idiot lights for the oil pressure and charge indicator on Big Blue. So, today I pulled out an instrument cluster of each kind. And, I think the answer is "It isn't gonna be easy!"

But first, a little bit of trivia and mea culpa:

1. It appears that 1985 was the last year for idiot lights as an option. At least that's what I gather from the EVTM's, as the 1985 version shows them and the 1986 doesn't. However, the master parts catalog shows idiot light cluster, marked E1TF 10C956-A, as going from 1981 through 1986. But, that may be an error in the catalog. Does anyone know?
2. I've been WRONG about the gauge clusters and tach's. Take a look at the first picture and tell me how a tach is gonna work on the bottom cluster when there's no printed circuit going to it. Turns out that there were clusters that would not work with a tach and those that would. (Dave, I've edited that post. Sorry. )
   
   So, the clusters are marked:
   • E1TF-10C956-A is an idiot light cluster with no wiring in the harness, much less the printed circuit, for a tach
   • E1TF-10C956-B is a gauge cluster - with tach wiring
   • E1TF-10C956-C is a gauge cluster, but no tach wiring

Ok, but what about the idiot light vs gauge thing? Well, count the wiring harness connections, circled in yellow, on the idiot light cluster, which is on top, and the gauge cluster on the bottom: 14 connections vs 18. So, you can't use an idiot light cluster in a truck wired for gauges.

But, maybe you can graft in the lights to a gauge cluster? Yes, I think that can be done by drilling holes roughly where the green circles are and soldering to the traces that are there.




But, here's how the bulbs are on the idiot light cluster and, as you can see from the next picture, there's a red filter with the wording on it, covered by a black bezel. So, somehow that would have to be grafted in.




And, here's what an idiot light cluster looks like with the filter and bezel in place:

 

If you get the lighting mounted in the cluster, then it's a matter of just changing the sending units to switches(I think you knew that already).

Just a bit of trivia you may or may not know; Later on Ford for some reason changed their oil pressure gauge to a "idiot" gauge. I have heard it was because of warranty claims, but I can't substantiate that. They still have the oil gauge in the cluster, but instead of a sending unit, they installed the oil pressure switch. And then branched with the sending unit wire on the cluster they installed a resistor.

No oil pressure, the switch grounded out and the gauge reads zero. Anything over 5lbs oil pressure, the switch opens to ground, and the wire to the gauge is pulled up to a mid value by the resistor. So anything over 5lbs oil pressure, the oil pressure gauge reads middle scale. Pretty neat ain't it?

 

Yes, the sending unit (sensor?) needs to be changed. But, since Big Blue is a 460 with electric fuel pumps he needs the switch anyway. And, the Standard Motor Products PS64 that came in today has NO and NC contacts. So, it could handle both the light and the relay.

As for the trivia, I'd read the same story. Not sure where I read it, but it does seem like something they'd do.

 

Yeah, all the lack of resolution of an idiot light without that annoying ability of an idiot light to get your attention! (the worst of both worlds, not one of Ford's "Better Ideas")

 

Well said!

 

Why would you want to downgrade from a gauge? Unless perhaps you have calibrated gauges installed and want a light to get your attention faster if you're distracted so you know to check the gauges?

Either way in my experience a catastrophic oil pressure failure is very rare and if it happens you'll know immediately from the noise. Most failures are gradual changes that you will notice while normally scanning the gauges. Either way, you'll know aobut a catastrophic failure immediately but a typical failure a light won't tell you until the damage it catastrophic. Alternator failures are not catastrophic and if you notice now or in 1 minute or 10 minutes makes no practical difference. Even if you don't notice until the headlights are dim you're not in for any more time or money than you otherwise would be. Granted if you've upgraded your alternator the factory ammeter is likely non functional, but you could convert it to a voltage gauge. Basically I fail to see the advantage to this.

 

These are the ID engineering numbers marked on the printed circuit boards, except you dropped the last letter of the suffixes (fixed 'em for you).

Whiz over to 10K843 and take a look-see.

Also look up 10848, the instrument cluster backs. One is listed for 1981/86 F100/350 & Bronco with Oil/Amp WARNING LAMPS.

 

This is the great thing about my '87 being a transition year.
I have an idiot light AND a real oil pressure gauge.
I have a Voltmeter AND a charge indicator light.

Anyway, with the redundancy of an aftermarket mechanical gauge pod it makes sense to have lights in the cluster.

 

Cadunkle - I have Autometer aftermarket mechanical gauges, so I don't need the ammeter nor oil pressure gauge. In fact, when I do the 3G upgrade the ammeter won't be usable. So, why not future-proof the truck for my grandkids, who won't have grown up with needing to scan gauges. In fact, probably won't even have had gauges. A big red light might get their attention.

Bill - You've spent too much time looking at the catalog and not the actual parts. Go look at the pictures I posted and tell me where the last letter of the suffix is.

Jim - You have the best of both worlds, but I may make Big Blue match yours. I say MAY because I haven't decided.

 

If I had another 86-dwn truck with the charge gauge, I would rather have the charge idiot light. That gauge never did show much of anything. If you throw a belt off, the light would come on and tell you instantly.

If you wait for noise to tell you you have no oil pressure, the timing would be the same as a oil idiot light really. But I do like a oil pressure gauge for trending as the engine gets more miles on it. That's a real oil pressure gauge, not the factory "normal" one.

I do like a temp gauge though. And I can usually deal with the factory "normal" gauges if you know your baseline and what is really "normal".

 

After looking up this jazz for 45 years, I know that 10C956 is the basic ID engineering number for printed circuit boards (basic part number 10K843).

It's not the ID number for cluster backs, instrument clusters, etc.

 

I turned the storage compartment in the instrument panel into a gauge pod and installed mechanical oil pressure and temp gauges. The oil pressure is connected to a T fitting so the factory gauge still works and I just installed the temp probe into an unused port so my original temp gauge is still operational as well.

 

Dave - I think we are in agreement. And since Big Blue has the Autometer gauges I do have both oil pressure and voltmeter. And big red warning lights would get the driver's attention much earlier than gauges - especially an ammeter that just barely moves with a 1G and isn't usable with the to-be 3G.

Bill - Yes, I said "cluster" instead of "PCB". My bad. But, none of mine have the second "A" or "B" that the parts catalog shows. So I didn't include it as I'm seeing what others are going to see.

Rowdy - That's exactly where Big Blue's aftermarket gauges are mounted. So you also have redundancy in gauges. Maybe you'd like to do this mod as well?

All: I've done a bit more thinking about it and it doesn't look as difficult as it first did. First, the windows in the bezel or mask measure .857" diagonally. So, two 1" tubes would work well to channel the light. And, the tubes could also act as the support for both the filter and the bezel. But, I'd have to mill off the raised plastic crosses and bosses for the gauge studs, as shown below, in order to have a place to glue the tubes down.




And, just for grins, here's a shot of the filter and bezel or mask.




And, I could use a snap-in bulb socket something like this:

 

I would not use that particular socket you have pictured. It only has one wire coming off it and requires it be mounted in something metal for the ground to the light. I would try to find something with two wires.

 

It was actually just an example, but I hadn't thought about needing a ground. So, good point. Thanks!