Vintage Ford Mustang Tech Advice May 2014 Exhaust
Bob Aliberto
May 9, 2014

Aftermarket Exhaust Clearance

I'm presently trying to squeeze a 2½-inch dual exhaust system under my '66 Mustang fastback. My concern is how close will the tailpipes be to the fuel tank? How much space is recommended for a proper and safe fit? Thanks for your help.

Frank Muth
Via the Internet

A 2½-inch tailpipe is a tight fit on an early Mustang and will require some patience to fit. Although the pipe gets hot, it will not transfer that heat to the fuel tank unless the pipe is physically touching the fuel tank. If the tailpipe is kept ¼-inch to 3⁄8-inch away there is not an issue. I would dimple or otherwise reshape the tailpipe in any area where physical contact could be made. The change to exhaust flow will be minimal at best but the danger of heating the fuel tank will be eliminated. Hang the system so there is clearance even as the system is flexed up and down in its hangers to be certain the clearance remains adequate.

Resistor Wire Bypass

I have a question regarding installing a DUI or HEI distributor in a '67 Mustang. I know the pink resistor wire is a no no with either of these distributors and before I commit to getting one or the other for my Mustang I'd like to know the best way to get around the resistor wire problem. I have read somewhere to run a length of wire from the Pertronix to the ignition switch, connecting it to the red/green stripe wire at the switch. Will this be the same procedure for one of these distributors? I have had lots of engine work done to my inline-six that is in the Mustang and I would appreciate some of your expert advice.

John O'Rourke
Kent Lakes, NY

The pink resistor wire is locating under the dash and is the power lead from the ignition switch to the positive side of the coil. Its purpose is to limit the amount of voltage going to the coil in order to reduce arcing and premature burning of the ignition points. Many aftermarket electronic ignitions do not require the reduced voltage and benefit from the elimination of the resistor wire.

Bypassing the resistor wire is easy, as it plugs into a red/green stripe wire pigtail located at the ignition switch. Simply unplug the pink resistor wire and install your wire from the red/green wire pigtail out through the firewall to the positive side of the ignition coil or HEI-style distributor. Be certain to properly insulate the loose end of the resistor wire, as it will be electrically “hot” with the ignition on.

Is He Hot or Not?

I'm scratching my head trying to figure out why my temp gauge on my six-cylinder '66 Mustang isn't reading properly. My Mustang is a complete restoration and I've replaced all of the wiring except for the under dash harness because that was in good shape. The radiator, hoses, thermostat, and temperature sending unit are all new. All of my other gauges are working so I'm assuming it's not the voltage regulator that bolts to the instrument cluster. I let the car idle for 30 minutes on numerous occasions and the needle sometimes will drop just below “C” and that is where it stops. Shouldn't the needle at least be positioned in the middle? All of the hoses and radiator are hot and you get that certain smell, so I know coolant is flowing through properly. Please note I have only driven the car up and down my driveway due to not having the car registered at this time. Any thoughts or ideas would be appreciated. Thanks!

Andrew Eldridge
Via the Internet

Stock factory temperature gauges are designed to be more of an indicator of coolant temperature than an exact reading. The gauges tend to be “individual” and differ from car to car. Your gauge is functioning correctly as it is indicating a change in temperature. A thermometer placed in the radiator will give you an exact temperature reading that can be compared to the dash gauge reading and will allow you to obtain a feel for your Mustang's temperature gauge reading versus actual temperature. If the factory gauge seems to be wildly off, then try changing the gauge sending unit in the side of the cylinder head. Sending units also seem to vary, so a change may help your gauge to be more accurate.

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Send your '65-'73 Mustang questions to: Beyond Basics, c/o Bob Aliberto, P.O. Box 205, Salt Point, NY 12578. Send email to