Oil Pressure Gauge and Tach Suddenly Dead

Howdy all.

Got Blue back from the shop. Gave up on bashing my head against the wall of electrical issues and sent it to be someone else's problem. Great, now it's back. Running, driving, wallet even lighter. Wonderful.

Two problems remain. The tachometer is now broken, and so is the factory oil pressure gauge. Both were working previous to this whole shebang, but that was about three years ago at this point, so...

Really just looking for tips on where to start.

Do I just grab a $20 oil pressure switch and whack it in? I'm pretty confident it's in the right place and the right wire is coming off it. My understanding is that it should be a single wire, maybe red on white? I also used teflon tape when putting in the old unit, which I now realize may remove the ability for it to create current and stop it from working. I do plan to get a secondary gauge set plumbed in somehow but I really hate looking at my dash and seeing zero oil pressure, even if it doesn't actually mean that I have no pressure.

As for the tach, slightly more complex. I'm going to assume the unit is fine for now and that any issues are from the source of current. Beyond that, I'm clueless. The signal should come from the distributor, right? So since it's stuck at zero, is it most likely to be a bad connection in the wiring from the distributor? (I'm using the distributor from the original motor so I'm 80% sure wiring is still good internally) The connectors are not in great shape because they're 37 year old plastic, so should I pull it apart, clean it with a rag and WD-40, and see if that fixes it? Failing that, where do I go?

Any help is much appreciated, and if no help comes, that's okay too. Thanks in advance for your time and efforts.

Ethan

P.S. As far as a Dana 60 swap goes, I'm becoming more and more interested. How much trouble is it? I'm having a hell of a time sourcing an 86-91 pattern D60 but I've heard those are the easiest. Should I bother? I'd go for the coil swap and keep the TTB but my wallet has other ideas. Thanks again.

Well, at least the other problems seem to be solved.

On the oil pressure gauge, the wire should be white/red.  It is the coolant temp wire that is red/white.  But you can ground the wire to the engine to see that the wiring to the gauge is good.  If the gauge goes up to full scale and maybe beyond then the wiring is good and you should replace the sending unit.  If it doesn't go up there's a problem in the wiring.

As for Teflon on the threads, if the gauge was working previously then the Teflon wasn't causing problems.  And I use a thread sealer on sending units w/o problem.

But the tach is harder to test as there isn't an easy way to do it.  I think you can take C323 apart and connect the dark green/yellow to battery voltage as rapidly as you can and the needle should wiggle.  But I've not done that and it might not work.

What will work to test the wiring is to pull the dash apart and ground the dark green/yellow wire on the connector going into the cluster.  If the wiring is good the engine will not run since there won't be any spark.  If the engine does run the wiring is bad.

But I wouldn't use WD40 on connections.  I'd use a Q-tip and alcohol to clean connections.  However, if you pull the dash apart then the connector that goes into the gauge cluster can be cleaned, gently, with an eraser on a pencil and then use alcohol.  The eraser will polish the copper.

As for the D60, I don't know what Blue is so can't comment.  But I will say that in my experience a TTB front suspension with leaf springs rides very poorly.  And a D60 with an RSK and SuperDuty springs rides much better.

Gary,

Thanks for the advice. Got after some of the wiring harness connectors with rubbing alcohol and q tips - nothing was super awful but I gave it a shot anyhow.

Can confirm the wire is white/red. Tried testing it without the engine running but key on by grounding it to the block but not much success - going to have to try again later with maybe an extra set of hands. Should I ground it with a separate wire out to the engine ground, and leave the connection to the gauge? Or should I do the same with the wire all the way off and the engine running?

As far as testing the tach goes, that will have to wait. Lord knows it may just fix itself on its own while I'm gone. I think matters are somewhat complicated by the fact that blue is a 460 truck and so not EFI - couldn't find an EVTM diagram that included a tach but not computer when I checked. Will check on the wiggle test first for sure as soon as I get the chance, though.

And finally, re: D60. Blue is an 86 F-250HD with the leaf sprung TTB, I believe a D50 because it has the big 4 and whatever inch hubs. The ride actually isn't terrible - much nicer than my 1st gen super duty one ton - but a d60 might be the most feasible way to get the tire size and lockers I want.

Thanks again for your help.

Just ground the white/red wire to the engine and then turn the key on.  The gauge should climb to at least full scale, and maybe more, in a few seconds.  If not the wiring or the gauge itself is bad.

As for the D60, an RSK kit like that from Sky Offroad and SD springs will get you ~2" of lift in the front, so your tires will fit easily.  And that's a good time to add a locker.