'81 flareside 4x4 project

I went with a cover from someone that did not use it. I think it looks good and am happy with it.

Unless you look for it you would never know it is a cover.
Dave ----

That really does look good Dave, was your dash pretty bad?  I ask because I'm not sure if the cover will stay glued with a really bad pad.

I also have been trying to figure out why my tach doesn't work most of the time.  It worked after a big rain for some reason but has stopped again.  The fuse for gauge illumination (18 I think) has no power to it currently.  Can't locate the wiring diagrams but it seems odd that everything in the fuse block has power except this circuit.  Any ideas?

You can find the 1981 EVTM here:.  https://www.garysgaragemahal.com/1981-evtm.html

This has all the diagnostics specific to your year (and yes, '80-'81 were different than later trucks)

Thank you, Jim!  I'll go through that and hopefully figure it out.

Tach signal should be a dark green/yellow dashed wire from the coil.

"worked a bit after a rain" . that seems to be a clue. certainly prove voltage but also check the grounds. there is a ground connection on the cluster itself where the gauge meets the film on the back. hopefully you will find it before getting that deep but i just point out that there are many connections and each can be the issue.

nmchuck wrote

That really does look good Dave, was your dash pretty bad?  I ask because I'm not sure if the cover will stay glued with a really bad pad.

I also have been trying to figure out why my tach doesn't work most of the time.  It worked after a big rain for some reason but has stopped again.  The fuse for gauge illumination (18 I think) has no power to it currently.  Can't locate the wiring diagrams but it seems odd that everything in the fuse block has power except this circuit.  Any ideas?

I think I used this one from my parts truck as I tried to use the one that came with my truck and I pulled some of the pad apart thinking the cover would fit better ........ it did not

I would say if where the cracks are are raised up to trim them or sand them flat so the cover will sit flat to the old pad.
Also wash the pad a few times and let it dry good before gluing the cover on.

BTW I had to graph part of my trucks non-AC dash on to this AC dash as it the PO cut / broke it to get the radio / HVAC controls out. Look at the bottom in the center.

Dave ----

ArdWrknTrk wrote

You can find the 1981 EVTM here:.  https://www.garysgaragemahal.com/1981-evtm.html

This has all the diagnostics specific to your year (and yes, '80-'81 were different than later trucks)

Jim I think only the 80 is different as most of my 81 looks to be the same as others when I have looked.
What is different has been where some of the grounds are and I think that was mostly for the tail lights.

Think the EVM has the ground for tail lights coming from inside the cab on the fire wall where my 81's were at the lights and did not have a ground wire in the harness.

I wonder if you have a bad connection under the hood and it got wet and started working?
I think there is the tach wire by the IGN box that sometimes needs to be plugged in.
What if you were to pull it apart, clean it and stick it back together and fingers crossed it works.
Dave ----

He's asking about the tach.
Maybe I'm wrong but I thought the cluster flex circuit was different in '80 and '81 model year trucks.

ArdWrknTrk wrote

He's asking about the tach.
Maybe I'm wrong but I thought the cluster flex circuit was different in '80 and '81 model year trucks.

I am pretty sure the 80 uses a different plug wiring to the cluster than the others and were the colors do not match.
Also want to say the wire count is different but not 100% sure as it could be between gauges and lights for the clusters?

I also say the 80 is different because when I installed the tach & printed backing into my non-tach truck it was from a later year truck and it was a bolt in.
I did not have to go switching or plugging in wires either, worked out of the box as they say.

Could check LMC on the printed boards and see what years they list it for.
I still think the 80 is the 1 year only for the wiring of the dash cluster.
Dave ----

Wow, that was a lot of work!  My dash pad is significantly worse than the one you put the cover on, hopefully I can get it to stick.  I plan on removing it this week and will take your advice on sanding it down and scrubbing it clean.    

Since my truck is an '81 I think it may be the more common version.   I have yet to figure out why there is no current to the fuse 18, although looking at the documentation linked, it appears this fuse is only for illumination.  Funny part is that the lights work in the dash, strange.

I believe it could be a ground issue too, although all of the other gauges work just fine.  Page 55 of the EVTM shows the ground behind the radio, I'll pull that apart to check it out.

I pulled both of the connectors that have tach wires at the ignition module and cleaned them up too, no change from that effort.  Wiring has always been my nemesis, but I'll keep at it.

Thanks for the help and suggestions!

I should give a little back ground on my truck.
Note anything built after Sept is the next years model.

It started as a 11/80 F100 Flare Side making it a early 81 model.

All the wiring is from my parts truck that is a 02/81 F100 Style Side long bed, also an early 81 model.
I needed to use the parts truck harness because of the duel tank is not a add on but built into the main & frame harness. I also thought the AC harness was built in but it is a add on.

Neither truck had the ground inside the cab on the firewall by the radio.
If they did I dont remember it in either truck.
So if your truck is an early 81 it may not have that firewall ground either.

But like I said of the tach install it was a bolt in and worked where if it was a true 80 model I dont think it would have worked?
For the most part I never looked at the EVM for my truck as I did not need to.

I did have help from here on wiring the blower fan switch, radio plug, they were cut out, and wiring in a clock as the clocks have 3 different plugs over the years and the clock I got off Ebay did not match my trucks plug.

I was lucky that my parts truck harness was in great shape so all I did was remove it from 1 truck, clean & checked it, and installed in mine.
I did not have a flare side tail light harness but did have a good style side harness so I used it to make my flare side harness.

When you do a 4 year cab off frame rebuild there is not a part that was not touched LOL
Dave ----

What did you use for G701 Dave?
I pointed it out to someone in another thread but was unaware that it didn't exist in 1980

My truck is from 09/80.  Maybe I have the unicorn...

Is it possible to use a VOM to see if there is a signal coming into the connector for the gauge cluster? If nothing else I can verify continuity to the ground wire just to see if that is good.

Tach signal is indeed ground.
I'm not sure if your VOM will mess with spark but it's worth a try.

Ok, I'm still stumped with my tach.  I have really studied the EVTM, basically it appears that the black wire with green strip serves as a ground (terminated at the distributor.  This wire occupies position 1 in the connector to the gauge cluster.  When I test it with my VOM, it starts off reading very low and then moves around and settles at around 12 ohms.  I have taken apart and cleaned all connections I can find and ensured the ground screw inside the distributor was clean and tight.

The ignition works just fine so I'm not sure where to go next. On the connector for the gauge cluster there is a second black wire attached to position 1.  Can't determine where that one runs, so not sure if it is a factor.

On a separate note, I did remove the dash pad tonight as well.  This pad is pretty rough!


I believe the interior color is called dark caramel, any recommendations on a coverlay color?

I also painted the gauge needles this weekend; thought they turned out pretty good.



Thanks for they help from you guys, still chipping away!

Maybe you're reading backwards through the coil windings?
Try taking the horseshoe connector off the coil and see if you still get the weird 12ohm reading.
Beyond that I'd try reading to the distributor and DSII connectors, with them disconnected.

Chasing electrons can be a challenge sometimes.

Sorry I'm late to the party.  As Jim knows, I've been on a cruise and have now come home with COVID.  I'm ok but am just now starting to come out of the fog...

The BK/LG wire is just a ground and it puts the tach into the 8 cylinder mode from the un-grounded 6 cylinder mode.  I don't know why your VOM wouldn't show it as a good, solid ground, but I suspect that it is a good enough ground to trigger the 8 cylinder mode.

So, what's the real question here?  I've not read the whole thread, but I do have the 1980 EVTM so might be able to answer some questions if I understood what they are.

This is from the '81 EVTM:

Like I said two days ago, I think he needs to be looking at the Dark Green /Yellow Dot wire (circuit 11)

That's the one coming from the coil to the ignition module.