"Cam's Ol' Blue"- 1986 F-150 Base Ex-State of Oregon

[1986F150Six]

I am late to this party... my son's 1984 with feedback system was "born" without a tachometer. I removed an instrument cluster from a V8 truck and was afraid to fool with the printed circuit, so swapped my son's gauges into the tachometer cluster rather than swapping just the tach. It was plug and play and the tachometer worked. All four of the tachometer terminals were left intact.

I suspect that there is a wiring fault [ground]? I believe that even if both ground terminals [G & 8] of the tachometer were grounded, the tach would still work, but incorrect scale.

I suggest you remove the tachometer and temporarily run wires to the terminals. I have done this under the hood. Run a ground wire to the "G". Run a wire to the coil [green wire] and connect to "Sig". Connect a wire from the "B" to a 12 volt source. Fire up the engine and see what happens.

[ArdWrknTrk]

You're correct.
Grounding "8" will only make it read wrong, it won't damage the instrument.

With a 300 there are only three connections we need to know about.
Now we do, and we know where they go.

I think Gary is right.
If the harnii aren't rat chewed, that single connector is the likely suspect.

[thefraze_1020]

I currently have the nut off the "8" terminal post because I was under the impression it should be disconnected for a 6 cylinder. However, I should mention that the tach cluster showed exposure to moisture, with a few spots of corrosion on the ribbon circuit, and the terminal nuts that came on it were rusty. Is it possible that the nuts being rusty is not allowing a good connection? If so, should I get new nuts for the back of the cluster and try again?

[thefraze_1020]

1986F150Six, are you saying I should unplug the green wire from the connector on the fender, then hook an alligator clip from it to the "sig" post of the tach?

[ArdWrknTrk]

I don't think it would make a difference.
The copper trace making contact with the base of the stud is what matters.

Can you check ground and hot in run?
Can you look at the #169 connector Gary pointed out?

[thefraze_1020]

I'm working today, but I will have the next three days off. So, I will pull the cluster, remove the tach and test it under the hood. Then I will check the C169 connector, and verify when I reinstall the tach that the terminal posts are making contact with the coppee trace. I thought that the connection went from the trace, through the nuts to the posts. Thats why I was asking about the nuts.

[1986F150Six]

thefraze_1020 wrote

1986F150Six, are you saying I should unplug the green wire from the connector on the fender, then hook an alligator clip from it to the "sig" post of the tach?

I was describing my way of testing a tachometer before the installation. Wiring directly to the terminals, without any part of the original circuitry being used, will prove if the tachometer is a working unit.

Way, way back, on another forum, a guy wanted to add a factory tachometer. He hardwired the tachometer as I previously detailed because the printed circuit [ribbon] he had was from a truck w/o factory tachometer.

[thefraze_1020]

I did most of the work on the clock, radio and tach last Tuesday. The following are some pictures from that. The first one is an overview of my wrecking yard goodies:








The first thing I did was remove the dash pad to rewire the digital clock pigtail:

[thefraze_1020]

Next I set to work disassembling both instrument clusters, swapping my gauges into the tach cluster from the wrecking yard, and reassembling:

[thefraze_1020]

As I mentioned, at that time the tach was not working, but all of the other gauges were.

Yesterday, one of my buddies came over and experimented to try to fix the tach. The first thing I did was unplug the C169 connector on the driver's side inner fender. I then hooked up my multimeter to a ground (brake line coming out of the master cylinder has served as a good ground for me), and the positive lead to the green wire on the coil side of the connector. We started the engine up and I had about 13.5 volts to connector C169. So, the wiring that far was good. I then assumed it was a cluster problem.

We removed the bezel and cluster, then removed the gauge itself from the cluster. I then set the tach on top of the air cleaner and ran alligator clips to it to test. A black wire from the ground post on the tach to the above-mentioned brake line. A green wire from the tach side of the coil to the "Sig" post on the tach. And finally a red wire from the positive battery terminal to the "B+" post on the tach. We started the engine and nothing. In desperation, I bumped the tach needle and it started to move like it was supposed to, although kind of sticky:








Cameron

1986 F-150 Base, 4x2, 4.9L I6, C6
1992 F-250 XLT, longbed extended cab, 4x4, 7.5L V8, ZF5 5-speed

[thefraze_1020]

I recall reading somewhere that one issue the gauges (tach in particular) have is sticky needles, gummed up inside. So I sprayed inside the needle hole on the face with electronic cleaner, moved the needle around and tested it again. This time the needle moved a lot smoother when the engine was running.

With a working gauge finally, we reassembled the entire cluster and bezel in the dash, and started the engine again. The gauge now moves like it is supposed to! So, as it turns out, it never was an electrical problem, rather the needle on the tach itself was sticky.

[thefraze_1020]

The next tasks are to try to bench test the digital clock and the radio. I have a good idea how to test the radio, but does anyone have a good way to test the clock? It's a 4-pin connector, but I am not sure which wire is which right off the top of my head.

[kramttocs]

Nice work on the tach!

Check this out on the clock:
http://www.garysgaragemahal.com/digital-clock1.html

[Sac79]

Congrats on getting the tach to work.

The W/P wire is power, should allow you to check the clock. LG/Y is memory and BR is to dim the display? I don't have one, so not sure what the brown does, but that's just my assumption going off the EVTM.

[thefraze_1020]

If one of those clocks does not work, is there a common thing that goes wrong inside em? And if so, are they repairable?

[FuzzFace2]

Sac79 wrote

Congrats on getting the tach to work.

The W/P wire is power, should allow you to check the clock. LG/Y is memory and BR is to dim the display? I don't have one, so not sure what the brown does, but that's just my assumption going off the EVTM.

BR is the dash lights for diming
BK (black)is a ground
LG/Y power all the time memory
W/P power with key to run & acc.

Now I don't know what year truck you have as the colors on the truck changed over the years
My 81 the BR wire for dash lights went to LB/R wire on the truck all the rest were the same colors.

I cant help on if it does not work or how to fix as mine, from Ebay, worked when I hooked it up.
Good luck
Dave ----

[ArdWrknTrk]

Really glad you've got it working!  

Sometimes Occam's Razor falls right into play.

[Gary Lewis]

Well done on the tach!  That may be the problem with other trucks as well.

[thefraze_1020]

I tried testing the radio today, no dice. With that said, I tore apart the radio so if anyone needs bits for a 1985-86 AM/FM/Cassette electronic radio, let me know. I have a good faceplate, buttons, and the casing.

[thefraze_1020]

Oh, and Gary, we are moving next week. So, you can change my location to Burlington, WA 98233.
Thank you!