We have three tips for you in this issue: How to minimize failure of your starter solenoid under high heat conditions, improving cranking with trunk mounted batteries and how to meet the NHRA requirement of a positive shut-off of your engine with the master disconnect switch. The three subjects are closely related and were deemed advisable to print them together. This results in a longer than usual column. This writer may now take a break from an issue or two.

Note: You may wish to review last months column on Pontiac Starting Systems for clarification on some of the following listed components’ operation.

Improved Solenoid Operation

If you have an erratic starter solenoid due to heat, a correctly installed Ford solenoid will provide maximum power to the Pontiac Delco solenoid energizing coil (“S” terminal). The idea is to eliminate the voltage dropping effects of all the “start” circuit connections through the firewall (bulkhead), ignition switch, Neutral Start position, and unknown lengths of wires connecting them. Each wire or switch connection will tend to drop some voltage due to wear and tear and/or corrosion, the bulkhead connections heat and expand, the neutral start switch becomes worn and the result is less than optimum voltage at the solenoid coil. The situation becomes more serious when the solenoid heats due to engine/manifold/heater heat, because a hot solenoid needs even more voltage to operate.

Mount the Ford solenoid securely to the firewall somewhere around the master brake cylinder. Assure it is grounded, or it’s negative coil terminal is grounded. If in doubt, run a ground wire directly to the rear of the engine head. Remove the factory wire from the “S” terminal (usually purple) on the Delco solenoid and reconnect it to the small positive coil terminal on the Ford solenoid. Using 12 gauge wire, connect the other large Ford solenoid post to the positive battery cable connection of the Delco solenoid. Use appropriately sized terminal lugs and carefully crimp or solder the wires into the terminals. As the Ford solenoid is only designed to operate a high current switch through the large posts, and does not have to throw the starter drive into engagement as does the Delco, it requires much less electrical power than the Delco. Accordingly, the multiple connections and switches in your vehicle’s start circuit have less detrimental effect and the Ford solenoid will operate more dependably. As the only connections in the Delco solenoid activating circuits are the “S” terminal to the Ford solenoid and the positive battery terminal to on the Delco to the Ford, maximum power is always available to activate the Delco solenoid coil. The effect of the Ford solenoid closure is the same as placing a large screwdriver from the “S” terminal to the positive battery cable, except without the ensuing sparks and bang. As 12V power is permanently connected to the Ford solenoid, carefully position it to minimize any accidental contact with the 12V. A remote starter switch or button can be easily connected, but a safer way is to use a temporary jumper cable only when needed.

Do not install the Ford solenoid in series with the existing Delco solenoid such that it also carries the starting current. Unfortunately, that has been the method many have used and some of the aftermarket kits even specify it. However, doing so adds one more source of voltage drop in the Delco circuit and makes the situation even worse. Use it to only activate the Delco solenoid! Do not waste money with a kit. Go to your local parts house and ask for a simple Ford solenoid. It may have only one small connector and the two large posts, and if so, the coil is grounded to the solenoid frame. If it has two small connectors, connect the start circuit wire to the positive one. This modification will cure most instances of intermittent solenoid failure due to heat while all original starting functions.

Trunk Mounted Battery Start Problems

If you have relocated the battery to the rear and encountered additional starting problems, the problem is likely the ground return path. Although it would appear the body and frame could easily conduct the required current to the starter, in reality, iron/steel is a much poorer electrical conductor than copper. Add in the higher resistance of welding and/or bolted connections, and deterioration of the same due to age and weather. Quite often, the starter will not crank a warm higher compression engine when the battery is grounded at the rear of the vehicle. The vehicles without full frames have even more serious problems of high resistance. The solution? In all cases, run the ground cable directly to the frame and connect it solidly through a clean connection. Connect an equal size cable from the frame close to the engine directly to a starter mounting bolt. (The normal frame to engine ground straps are not large enough to handle starting current.) If this does not solve the problem, run a ground cable equal in size to the positive cable directly to the starter mounting bolt from the battery negative post. The required starting current of approximately 500 amps simply will not conduct through old rusty frames and bodies as easily as it will through adequately sized copper cables.

Power Shut-off Switches For Rear Mounted Batteries

NHRA rules specify that a 12 volt power shutoff (master disconnector) switch be installed if the battery is relocated to the rear of the vehicle. The switch is to be located in the positive wire close to the battery and easily accessible from the outside rear of the vehicle. This rule is intended to allow drag strip safety personnel to immediately shut down a vehicle in case of an accident. The NHRA rules state that the switch shall stop all electrical functions in the vehicle. A literal interpretation of the rule means the engine should immediately stop running when the switch is opened and some tracks enforce that requirement. Unfortunately, the engine on any vehicle equipped with a standard operation GM Delco alternator will not stop when the battery is disconnected. Once energized, the alternator will provide more than enough power to operate the ignition system and keep the engine running without a battery, even at a slow idle. (Have you tried yours?)

A master disconnect switch that has two sets of contacts (Double Pole — Single Throw) can be used to meet the requirements on all GM vehicles utilizing alternators with external field wiring. The battery positive cable is connected across the set of high current contacts on the dual switch, and the “field” wiring for the alternator is opened and switched through the second set of contacts. Actuation of this switch removes power from both the battery and the field winding of the alternator causing the alternator to stop charging, and the engine will immediately stop.

To install the two pole master disconnect switch, perform the following steps, and then follow steps appropriate for the type of alternator you have:

1. Install the switch on the outside rear of your vehicle.

1. Fabricate a short section of battery cable and disconnect between the positive battery terminal and one large stud of the switch.
2. Connect the battery cable (running to the front of the vehicle) to the second large stud. Use brass crimp type connectors for the battery cable and crimp them with a hammer and small drift or punch. Carefully insulate both terminate with shrink sleeving.

2. Alternators with internal regulators:

1. Internal regulator units have the Field (F) terminal permanently connected to 12V. On these vehicles, cut the field wire (normally dark blue) between the alternator terminal (marked F and/or 2) and where the wire disappears into the wiring loom on top of the engine. Connect a new 14 gauge wire to the wire from the alternator field terminal, and route it to the rear to the new master disconnect switch. Connect the new extended field wire to one of the small studs using a ring connector either crimped on or soldered to the wire. Carefully insulate the cut end of the original field wire on top of the engine and tuck it into the wire loom.
2. Fabricate a short jumper using the same type wire and connect it between the second small stud and the large stud that is connected to the battery cable noted in step 1.B. (cable running to the front).

3. Alternators with external regulators:

1. The external regulator provides voltage varying from 0 to 12.4 volts to the Field terminal on the alternator. The circuit (dark blue wire) from the regulator Field terminal to the alternator Field terminal must be opened/closed by the new disconnect switch.
2. Cut the wire between the alternator field terminal and where it disappears into the wiring loom on top of the engine. Connect the alternator field wire to a new 14 gauge wire and route it to the rear of the disconnect switch. Cut the Field wire between the regulator field terminal and where the wire disappears into the wiring loom. Connect a second new 12 or 14 gauge wire to the regulator field wire and route it to the disconnect switch. Connect the new wire from the alternator field terminal to either of the small studs and the wire from the regulator field terminal to the remaining small stud on the disconnect switch. All connections should be crimped and/or soldered and insulated.

The net result of these wiring changes provides exactly the same voltage to the starter and alternator field as does the factory wiring when the master disconnect switch is in the “ON” position. When the switch is “OFF”, the battery is disconnected from all circuits, the alternator stops charging and the engine immediately quits. There are no current surges that might damage an ignition system, and all power is disconnected from the master switch to the front of the vehicle.

Many commercial items of off road equipment, and industrial in-house freight moving equipment, use the double pole master disconnect switch. Cole Hursee Company makes a double pole switch that meets all the NHRA requirements under their Part Number 75904-01. It is weather resistant, has a manual operated level (no Key lock), and is rated 1000 amps intermittent, 150 amps continuously, through the large studs, and 20 amps continuous through small studs. An ON/OFF plate should be ordered with the switch. Other companies undoubtably make similar switches, so check with material handling or earth moving equipment dealers. Thanks to fellow racers Gary Carnivale, Kevin Kirk and Don Green for help in resolving a method to meet NHRA rules and in identifying the switch.

Self-energizing alternators (one wire alternators) have no field connection to open. In order to meet the NHRA requirement to kill the engine with the master disconnect switch, the alternator out-put must be disconnected from the vehicle electrical system in the front of the vehicle and routed to the battery positive terminal on the disconnect switch. When the switch is in the “ON” (normally closed) position, the alternator charges the battery and power is distributed through the battery positive cable through the solenoid. When the disconnect switch is turned “OFF” (opened), both the battery and alternator outputs are disconnected from the ignition system (and all other systems) and the engine automatically quits. A single pole high current disconnect switch is satisfactory in this case. Although this change will meet the NHRA requirement, a minor safety concern remains. The alternator output wire from the battery to the alternator retains 12V even when the switch is opened. Hot Rod Magazine discussed a more elaborate version of this modification in the June 1996 issue.

If you know of more NHRA approved methods to immediately kill the engine when the disconnect switch is switched “OFF” while using a functional Delco charging system, please contact me and I will pass it on to other readers. Any device or operation that requires the driver intervention at any time will violate the NHRA intent, because the driver will be unable to do so if incapacitated in an accident.