I just acquired an 87 GT Hatchback for restoration. The car is in pretty good shape with a few exceptions. The problems I am having are as follows:

1) The tachometer displays incorrectly (like 4k at idle and way in the upper red when I slightly rev the engine. could this be a printed circuit issue, a missing resistor or ??


2) When I bought the car the prior owner said he was charged $1000 to trace down a short that was found in one of the instrument cluster panel illumination lights. The gauges all appear to display correctly until I turn on the headlights. At this point the tach changes revs, the left turn signal indicator light stays on, all the gauges peg out, and only the right side if the instrument panel illumination lights work. I notice that if I slide the dimmer control back and forth it effects the gauges as well. I have not taken the cluster out yet but I did need to tighten the steering wheel shaft and when I removed the lower column trim I noticed someone had spliced in wires leading to the multifunction switch on the column. I purchased a Haynes manual and it does not even list the tach in the wiring diagrams or the wiring for the printed circuit on the back of the instrument cluster.

I would welcome any suggestions regarding these issues and need to be steered to a source for a good, complete wiring diagram for this car because the haynes one isn't sufficient.

Also, this car has the 85mph speedo so i have been looking for an 89 instrument cluster (complete) with 140 mph speedo.

Thanks in advance guys. I'm new to the site but am sure I will be a frequent poster.

 

You're welcome.

http://www.veryuseful.com/mustang/tech/engine/

Replace your dimmer switch. They are prone to failure after this many years. You can get em cheap sometimes in the classifieds or on Ebay. That will solve that problem. And rewire the wires from the multifunction switch back to original. Maybe that can help.

 

The module on the column on the right side (held on by 2 tamper proof torx) also could be faulty. It controls some of the power going to instruments and to the multifunction switch. I had mine break internally, I found it feeling it was loose, when I took it off and unplugged it, it fell apart in my hand.

 

i wouldn't replace anything yet.

you say this is a project car, so what you need to do it remove your entire dashboard and start tracing. look for obvious problems. you sound like you have 3 or 4 wires in a harness together somewhere that got shorted and burnt and fused a few together, including a ground.

i chased a problem like this on a 95 bonneville ssei
that freakin fully electronic dash is no god damn fun

 

Thanks guys for your fast replies..keep em coming. The last car I restored was a 68 Z-28 back in 1989 and the wiring was A LOT simpler. I have an 89 Cluster coming with a 140mph speedo that is in excellent condition. I figured if I was going to get down and dirty in the wiring i might as go ahead and get the updated speedo. From what I have read the 89 should bolt right up with no modding. Is this correct? Heres the cluster:

http://cgi.ebay.com/ebaymotors/ws/eB...10497&rd=1

Another question. Does the mutifunction (tree) switch come with the harness that goes down the column? I would rather have to pull the steering wheel and replace the whole unit then splice the wires back.

This is a project car that will be a daily driver once I finish it so I want everything 100% when I finish

 

What were the symptoms it was showing before you found the module broken?

 

THANKS for the link! Now I have a starting point!! You rock!