Gauge swap, then bad idle

[maxford]

95 2.3L, 5spd.

My gauge cluster is the simple one without the Tach. The fuel gauge has been broken since I bought the Ranger a couple of months ago. It's pegged on E. yeah, its probably the tank sender... but I thought hey, I'd like to upgrade to a cluster with a Tach and I've read many of the reviews saying the swap is seamless. So I thought maybe there is a slim chance I have a gauge problem that would disappear with the upgrade.

So I ordered one from Ebay. It looked good enough. I plugged it in and started the engine. (note, it was loosely laying on the steering column for the "test"). The fuel gauge didn't work and the coolant gauge didn't work and the tach was ratcheting a little when I accelerated. But the most noticeable difference was the "check eng" light being on and the engine idling rough.

With the engine running, I disconnected the gauge cluster and the idle smoothed out. I plugged the old cluster in with the engine running (I know, I know, but I wanted to see how this could affect the idle) As I plugged in the old cluster the idle maintained its relatively smooth tick over. To check this, I unplugged it and plugged the replacement unit back in and "bam" the stumble/missing came back along with the check engine light.

Well, I cleaned up my old gauge cluster and fixed a few of the burned out back lights and put it back in.

Why would the replacement cluster cause an idle quality change which in turn must be causing the check engine light?

 

[tomw]

There are more differences than the cluster. The wiring for the alternator is different, as is the wiring for the (ignition)tach. If you connect something to the wrong wire, it will not work as advertised.
To do the swap, you'll likely have to have a complete wiring diagram of the cluster(both, actually).
I did this type swap(to gain a tach) on an Escort quite a while ago. I had to solder wire to the plastic 'circuit' on the back of the cluster to get it to work. Soldering plastic coated with 'conductor' is no fun, but I lucked out.
You may be lucky, and not ruined some other circuit you have yet to find out about.
Get the schematics/diagrams and work from there.
tom

 

[RonD]

+1, wiring "can be" plug and play but 90% of the time it will not be

You need wiring diagram for your '95(see below) and the "new" cluster, what Year is it?

In 1995(and up) the computer had the Tach pulse(ignition control module)
1994 and earlier it came from ICM on intake or distributor