1980 F350 4X4 C6 Project

[Atlas75]

I got everything wired up the way I wanted it and reinstalled he cluster.  I fired up the truck and the tach worked!

Next I drained the black fluid like substance from the rear diff and cleaned up the mating surfaces and reinstalled the cover and refilled the diff with new fluid. I also futzed around with a few other things including installing the trim around the cluster.

Time to start the truck and park it next to the trailer…and the tach no longer works.

I guess I’ll be pulling it back out and double checking everything.  I hope it didn’t get ruined somehow.  

[Gary Lewis]

I doubt it got ruined.  Probably just a connection issue.  Like maybe your ignition switch didn't come all the way back to Run.  That happens a lot in cold weather as the grease in the switch and the linkage gets stiff.  There are multiple contacts in the switch and the ignition contacts always seem to make before the accessory contacts do.  So it isn't unusual for a lot of things not to work if you don't roll the switch back a bit more.

[Atlas75]

After reading your post I think I should have done things differently.  I took battery literally and connected “B” to an unswitched 12 volts (I tapped off the electric brake controller which has a wire direct to battery).  Switched 12 volts would make more sense.  I wish I would have paused and thought about it for a minute.  I wonder if the tach will draw power when the truck is off?

[Gary Lewis]

It'll draw some.  But if it has power all the time then the ignition switch isn't the problem.  

[Atlas75]

How do the heater controls come out of the dash?  They are mounted behind the metal part of the dash.  Do they come out the bottom somehow or do you need to disassemble most of the dash to get them out?

[FuzzFace2]

Atlas75 wrote

How do the heater controls come out of the dash?  They are mounted behind the metal part of the dash.  Do they come out the bottom somehow or do you need to disassemble most of the dash to get them out?

If you ask the PO of my (parts) truck he broke the dash to get it out.
I had to graph part of my old non-AC dash into the AC dash I needed to use.

I really dont know as I installed the HVAC in the dash before I put the dash in the truck.
Later I needed to pull it for something and gave up.
I cant remember if it will come up through the radio opening or not as I think I still had the radio installed and did not want to pull it to find out.

Good luck and if you find how it comes out post it up.
Dave ----

[Gary Lewis]

The factory service manual (Documentation/HVAC/HVAC Systems and then the 1981 FSM & the A/C-Heater Systems tabs) shows the procedure below:

[Atlas75]

I got it out.  The ash tray needs to be removed and then you can tip the back of the heater controls up and drop the front down and it comes out.  It’s tight but it comes out.  Thanks for the help!

[Gary Lewis]

Yep, that was part of Step 4.  But you didn't have to take floor register duct out?

Anyway, glad you got it out.  

[Atlas75]

I did not remove any ducts.  That may have made it even easier but I did get it out without removing them.

[Gary Lewis]

Good to know.  Thanks.

[Atlas75]

Going back to the tach…my test light is telling me that the 12v supply and the grounds are all good.  I have yet to test the tach signal from the coil all the way to the tach but I did trace it under the hood and it was getting as far as the connections by the duraspark box.  Hopefully tomorrow I can check it at the tach.

If it is bad I bet it got ruined when I jumped the vehicle with the tach connected to battery.  So much for my great salvage yard find…maybe!

[Gary Lewis]

I hope the tach is fine and the problem is elsewhere.  Good luck!

[Atlas75]

Well it’s confirmed.  I have tach signal at the tach so I must have smoked the tach.  Well…live and learn I guess.

I have another question.  Neither my factory temp gauge nor the aftermarket temp gauge have worked since I bought the truck.  Today I replaced the old aftermarket gauge with a new one and it doesn’t work either.  Now I am starting to think something else is going on.  Where should the aftermarket gauge be plumbed in?  I put the new one right where the old one was, which is on the radiator side of the thermostat about 2 inches past the thermostat.  Is that a proper location?  If the thermostat was missing or stuck open would the engine get hot enough to register on either gauge?

[Gary Lewis]

Bummer!  Sorry about the tach.  

As for the temp gauge, if the factory gauge worked then having another gauge after the thermostat wouldn't be an issue.  But I believe you need at least one gauge monitoring the engine's temp, and after the 'stat wouldn't show engine temp if the 'stat were to stick closed.

I have both the factory and the aftermarket gauges ahead of the 'stat on Big Blue.

[Atlas75]

Do the 351M and 400 use the Cleveland style thermostat?

[Gary Lewis]

Yes!  See the page at Documentation/Cooling Systems/Thermostats. And that has a link to the 351M/400 page IIRC that has pics.

[FuzzFace2]

You didnt use sealing tape on the sender did you ? they need to ground to the motor and the tape can stop this.

If you ground the sender wires and turn the key on do the gauges move?
If they dont move you need to work back to the gauges.
Do you have power to the after market gauge?
Dose the fuel gauge & oil gauge work?
Dave ----

[Atlas75]

Oil and fuel gauges work as they should.  On the aftermarket gauge I installed, I did not use any pipe tape and the only power needed is to run the back lighting if needed.  This particular gauge has the ether filled line from sender to gauge.  

I have not done anything to the factory sender.  I did find a troubleshooting guide in my 1980 EVTM but have yet to perform the test.  I will also try grounding the wire on the sender to see if the gauge moves.

[FuzzFace2]

Atlas75 wrote

Oil and fuel gauges work as they should.  On the aftermarket gauge I installed, I did not use any pipe tape and the only power needed is to run the back lighting if needed.  This particular gauge has the ether filled line from sender to gauge.  

I have not done anything to the factory sender.  I did find a troubleshooting guide in my 1980 EVTM but have yet to perform the test.  I will also try grounding the wire on the sender to see if the gauge moves.

Well if the after market gauge is a mechanical there is no reason why it should not work
Unless it is not in water to pick up the heat?
Boil a pot of water and dip the sender in it and see if it moves. If not bad gauge.

On the factory grounding the wire is the easiest way. If you have a test light you can put it on the wire and to ground and it should blink if all is good back to the cluster.

They say you can also swap the oil & temp wires on the senders as the gauges are the same just marked oil & temp but work the same.

My factory oil gauge stopped working today just have not done the testing to see if gauge (hope not) or the 2 year old sender.
Dave ----