So After a few years away from my old 91 F150 300 Custom 5 speed, I got this nice 90 Lariat 4x4 with the 351 Auto. Truck runs great, has a few items I would like to address. I am sure I will have some more threads coming up soon. And yes for the past week I have put my left foot almost through the floor because I am so used to putting the clutch down when I start it up...

Anyway I always wanted to have a factory tach on my 91, and I never did it. Now I have this I just have to have it So the local pick and pull had a few trucks and one truck same year had one. However it had the 300 in it. So the factory cluster I pulled was from a 300 I6.

I plugged this in to my truck and the needle sits nicely at zero, as soon as you turn the ignition to run it jumps to 3k and when running it sits at 3k. I rev it up and it will jump up to maybe 3.5k, the truck is probably not turning that fast Im guessing around 2.5k.

I have searched and searched and cannot find any help on this. I know it has been covered, or at least I am sure this has been covered, usually from the V8s to the I6's.

Any help with links would be very appreciated. Here are some pics to tide you over from my $900 find. My 2011 with the 6.2 is hiding in the back ground as well

 

Still not sure what the deal is. I took the tach apart and it says on the back it is for 6 cyl and 8 cyl

think its it’s just a bad tach?? Or is my trucks wiring bad

 

My guess would be a bad tach.

 

In the 1980-1986 trucks, the cluster is the same for a six cylinder engine or a V8. However, the V8 has an extra ground wire in the harness so it will "read" correctly for a V8. Six cylinder engines did not have the ground wire. If the ground wire isn't there, the tach will read too high for a V8.

Maybe the 1987 - 1991 trucks is similar?

 

So I’m leaning away toward a bad tech now. As I got another use the Cluster same year 5 L and it does the same thing

 

Does anybody happen to have a factory wiring diagram? That would be really helpful to trace this down

 

Updating this, I went through 3 junk yard clusters before I found one that worked! I pulled all the available ones in our area and found 2 clusters with the tachs that did not work. Both tachs did the same thing, they would jump to 3k RPM when i started the truck.

Honestly I was thinking this was a wiring issues. Figured I would try the last cluster and it works perfectly. So to recap if you have a tach that is jumps up to 3k or any number really it is likely bad.

Thanks to Subford who helped me out with some wiring diagrams and to walk me through this problem!

Got some of the interior cleaned up. Still has some work to do but its much better now. Also got the exterior just washed. As you can see it's at least white again! She should polish up nicely.

Stopped by LMC truck, they are about 15 min away and picked up the cab corners and some repair panels for the bed sides. Looking forward to trying my hand at some body repair.

Got the drivers power window motor replaced as well. Pretty easy job.

Any advice on cleaning up these aluminum rims? I got some new center caps and lug nuts.

 

Got the rims clean d up and polished. Got the diffs topped off and the transfer case. Also got the rear shocks replaced and the tail lights working again. Had issues with the previous owner trying to install an trailer harness.

Enjoying this truck.

 

Your rims cleaned up real good. They look great.

 

Thanks Glenn! I was suprised honestly how well they did clean up, but after all they are real metal instead of plastic covers like the new stuff!

Wife couldn't believe it either. Said they don't match the rest of the truck now...

That will change. Got some new metal to weld in and gonna have some fun here soon!