Can anyone direct me to info on how to swap out a idiot light 100 mph speedo cluster to a gauge cluster on a 1975 f250.
Any help appreciated.
Thanks in advance.
Tbruz

 

I believe you will need a completely different under dash wiring harness due to sending unit differences and a complete different instrument cluster.....easiest to just get a set of aftermarket under the dash gauges. Oil pressure, temp, alt tap in and go.

Unless you can do some magic and get a lone aftermarket gauge and put it in place of the idiot light, but that will involve instrument cluster surgery.

 

Yeah, it's not easy, and you have to do something with the ammeter, like swap it for a volt meter.

But not impossible!

I grabbed a cluster from an econoline van and the connector (cutting the wires) and studied the wire schematics. I used a small jewelers screwdriver to remove each wire from the connector (easy) and plugged them into the junkyard connector. Then swapped the Oil sender switch to a gauge style sender, and off I went!

Attachment 290205

I did go one step further into crazy and used '90's style gauges that require 12volts and grounds...

 

Rich is correct, to do the swap you will need to change the main, under dash wiring harness and also the alternator harness. You will also need to swap the oil pressure sender for one for a gauge.
This is a lot of trouble to get two extra gauges who's accuracy is so-so at best. The ammeter is so ineffective that Ford actually published a TSB (technical service bulletin) on it.
Unless you're going after originality, I would use a set of good aftermarket gauges. Faster, easier, cheaper, and definitely more accurate than the factory units.

 

I am definitely going for originality, but it sounds like this is more effort than the value it gives back.
4 gauge Cluster appears easy to find on line, replacing a sending unit is easy as well.


Do I really need to replace a harness or could just add some wires and re-pin a connector as mike0o0o0o has suggested.

Where could I review the schematics to decide if I want to pursue this?
Thanks
Tbruz

 

Well then leave the warning lights in the cluster to have it original. The factory gauges are not all that reliable anyway.

Schematics are here and some other things.... https://www.ford-trucks.com/forums/1...then-some.html

 

That's not what I suggested.
The reason you need to change both harnesses is the ammeter is a shunt style meter. It doesn't have the full output of the alternator flowing through it like most aftermarket gauges. There is a shunt wired into the alternator harness that senses the charge rate of the alternator and this is what the gauge sees.
That's why you need to swap the harnesses.
Go here to look at factory wiring schematics. 1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net

 

Might take a gander at some things from 80-86 (this question comes up there, too, and the answers are the same):

https://www.ford-trucks.com/forums/1...olt-meter.html

Rocketman's Classic Cougar Innovations

Ammeter to Voltmeter Conversion

 

Might read this, too... it *has* been done but requires some rewiring of your charging system:

https://www.ford-trucks.com/forums/1...ck-answer.html

 

Good info and good reading.
Thanks
Tbruz