circuit board problems

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rdm1952

Well-known member
Joined
Jun 24, 2016
Messages
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Location
missouri
My Car
1971 Mustang Mach 1
My 1971 Mach 1 had dash light problems. In removing the dash to replace and check on things I found that the circuit board was modified from a non tach board to a tach board and they used jumper wires to connect the dash lights. I assume just getting a new tach circuit board would do the trick but the resistor seems to be right in the middle of of where the tach sits. What am I missing here?

 
There's more involved...the true tach circuit card accepts a 12 pin dash cluster connector, not the standard 18 pin connector. The underdash harness has to match the dash cluster/circuit card for the wiring to be correct all-the-way-around.

What do you mean by the "resistor seems to be in the middle where the tach sits"? Are you referring to the constant voltage regulator?

Are you sure you have a Ford tach dash cluster? Are there two wires coming out of the tach pod? If not, someone inserted an aftermarket tach in there.

 
Sorry about that, you are right the voltage regulator. There are two wires coming from the tach. Has a Ford part number on the back of it. Trying to figure out how to post pics.

 
OK..someone earlier has replaced the dash cluster pod with a tach pod, without changing the overall dash cluster. Buying a new tach circuit card won't help as the dash cluster connector will change to a 12 pin affair and your underdash harness doesn't have that. There's more wiring changes in the underdash harness as well. Ugh...that's a mess to make correct. If it works now, leave it alone and pray it doesn't break. But you say the dash lamps don't work...look for a broken trace somewhere.

 
Thanks for the info. I was just hoping that he just put in the wrong circuit board and modified it to work. What do I look for in the dash cluster connector to see what I have there?

 
Are all the lights non-functioning? Or just around the tach? It doesn't look like there are many lights on the tach side. I see the brake light and maybe 1-2 more. These lights are SO dim already, perhaps you couldn't tell if they are working or not?

 
There is a simple solution. Go to Rocketmans Classic Cougar Innovations and you can order a modified Tach and Idiot light module that fits right in. You would just need to run a ground wire to the neg side of your coil and follow the simple wiring connections. This is what I did and it works awesome. While your at it, buy a set of Hi-PO Elite LED's (NPD sells them), but do NOT put an LED in the ALT socket. This must be a regular bulb.

Picture attached. ( I do not use the brake warning light)

Rocketman is a member here also. I forgot to mention that he may take your tach as a core return if it meets his criteria.

 
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This diagram is for information only. I do not want to upset HiPo parts.

Note: the ALT position shown is incorrect. ALT is the bottom right bulb location.

 
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