Ok...as you can see from the title I have a 90 F250. My problem is this. The guy that i bought the truck off of changed the engine out from the original 351 EFI to a carbed 460. now my problem is the tach does not work anymore. I would like to know if the factory gauges ran threw the computer, or if the tach is just connected to the coil?

Also if the tach is in fact ran with the computer, can i make it work by wiring it up to just the coil?

one more thing, I'll be changing the oil in the truck really soon and was wondering what people use for a "engine cleaner"...trans fluid, kerosene, motor flush stuff you can buy from the store? also what is everyone using for oil...I have an older cutlass ( RWD) with a 350 olds and i've had really good success with using 15-40w Rotella T diesel oil. Thanks

Justin
New Baltimore, MI

 

None of the gauges go through the computer.
How ever they did run through a Ignition Suppression Resistor Resistor, E9DB-14A601-FA.

See diagrams below and look at the red boxes.





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Thank you for the reply.

But would you mind helping me out one what the Ignition Suppression Resistor really is or does? does this mean I can or can not still hook up my tach ?

Thanks

Justin
New Baltimore, MI

 

A resistor is used to drop voltage, not sure why it is used here. You may already have it but it may not be hooked up. You should be able to get one from a salvage yard or from FORD if you do not have one. I would use the resistor in the line (wire).

 

Thanks...I'll have to check to see if its still there. If im not mistaken...this resistor would be under the hood on the firewall correct? I believe I remember seeing one there.

Thanks again..

I'll keep this posted.

justin New Baltimore, MI

 

It was located on the 460 engine at the LH (drivers side) of the engine taped in the harness near the distributor.

That would mean that it was in the engine harness. If the engine was changed like you say the engine harness is more than likely gone along with the resisters.

Sounds like you need to find the end of the tach wire under the hood, put a resister in with it and run to wire to the coil tach side.

 

Yea i guess i should have stated the engine came out of a 78 Lincoln.

 

Does anyone happen to know what color wire(s) are for the tach under the hood? I think i read somewhere it was a two connector with a green wire and a black wire. Is this correct? thanks

Justin
New Baltimore, MI

 

I gave you all of the colors of the wires in the two diagrams above. The wires changes more than once. You also have the wire for the number of cylinders that you have.

You have :
R/Y = Red wire with a Yellow stripe.
BK/Y = Black wire with a Yellow stripe.
DG/Y = Dark Green wire with a Yellow stripe.
R/LB = Red wire with a Light Blue stripe.

 

Im going to bring up this again i have the same problem efi converted to carb 1990 my tach in the truck does not work, i have a parts efi wiring harness but am clueless on what wires go to where on the drivers side fender??? the diagrams above dont work anymore??? I really dont want to have a huge tach mounted on my steering coulum and on in the dash thanks guys sorry to bring up the old topic....
Donnie

 

Images restored above.

 

Thanks for posting pictures again, very very clear and understading i found everthing i needed the coil to resister, resister to fender connection to dash console... fail.. even pulled a dash from the junk yard today no go (((( has this been done successfully????? Anyone???

 

Do you have a 12V test light and/or a multimeter?

With the engine running at idle, probe the coil-side of the resistors with the test light, it should be flashing (light may not go all the way out, but should pulsate).

On the tach-side of the resistors, if you have a multimeter that will read AC voltage, put it on a low scale and you should be able to read a voltage there. You should get this same reading at the tach pin on the cluster as well (with the other lead of the multimeter connected to a good ground).

I'm wondering if you may have a bad ground to the cluster or maybe an open-circuit between the resistors and the cluster. Something is not right and you've got to do some basic electrical troubleshooting to figure it out.

 

Either it's not posted in this thread, or I am missing something. But I am looking for the wire that goes to the tach sensor? I was told it's a green wire but I can't friggin find it.

 

Someone must know where the tach wire is?