Road Runner Nest

hello back in 1996 i was a little under the influence of alcohol and hooked my tach wire up to pos on coil and fried it.what did i fry a solenoid or something is it easy to fix.sucks not having a tach and a new one is over 300 bucks.love to hear your input yes i know it was stupid was a kid back then and not wire friendly.

Did you have a factory tach, cause the wire would never reach the engine. A factory tach hooks in at the bulkhead connector, cause it was an option it had to be easy for the workers to add to the instrument pal quickly. Get a service manual and it will show where it hooks up in the wiring schematic. And if you have an after market tach you could hook it up the same I guess.

I guess you mean on the engine side of the wiring - engine harness - you connected the gray tach wire to the coil + instead of -.

The + side of the coil is at battery voltage when starting, then at a reduced, sort of variable voltage when running via the ballast resistor. That voltage jumps around due to the current spikes in the coil each time a plug is fired. I suppose it could fry the tach.

If that's the case, there's no easy fix. Have it sent out for reconditioning - not sure if they can fix the fried electronics - OR, find a replacement.

For a '71 - '74 Rallye Dash, Classic Industries has their own drop-in replacement, #MB323, for $200. They have fairly frequent promotions with as much as 30% discounts. I bought one a little while ago, but haven't installed it yet. In my case, I'm replacing a non-working clock.

You might try hooking up an aftermarket tach to confirm that your wiring is correct. The gray tach wire uses bulkhead disconnect terminal #20. On the tach end, only two wires connect to the gage - +12 V from the "ignition" circuit, and the gray tach wire. Ground is accomplished via the mounting screws into the back of the cluster, which is sheet metal. There are two lamps in the tach, also.

thank you guys for your answers and info.have a great weekend.gonna check out Classic Industries..ill look through their catalog thank you again.found the tach harness wires part MB 322 for35 bucks may as well replace as well and OE tach MB323 for 200 bucks like you said very cool