"Push Gas To Start" with an Alternator
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This page is all about preserving the "push gas to start" feature on older Buick's when you convert from a generator to an alternator. This is all strictly theoretical - I have not yet had a chance to complete this conversion on my Buick and test it out. It is based on my head scratching to date and the input of people on the BuickNailHead mailing list who have done this and gotten it working. This is all "FYI only" and no guarantees are provided that this is all 100% correct - my disclaimer is that if you try this on your car and mess something up, it's not my fault. :-)

Some background for those not familiar with this unique feature - on all Buicks from sometime in the late 40's or early 50's until 1958, the way you started the car was to turn the key to the "on" position and then depress the gas pedal until the car started - the starter would disengage automatically once the engine was running. There was no "start" position on the key nor was there a separate button to operate the starter - a very slick feature, indeed!

This feature used three major pieces to make it work. These three pieces combined to produce the required safeguards that the car was not running (via both a vacuum and an electrical detection) and that the throttle was being operated before the starter would engage. The first piece was a relay that operated the starter solenoid - when this relay was engaged it put +12V to the solenoid and starter assembly. The second piece was a combination electrical and vacuum switch mounted on the carburetor - the switch was only "closed" when the throttle was not at idle and there was no vacuum present in the carburetor. The final piece is the one we are concerned with here - the wiring to tie this all together. That is because the relay coil was "grounded" through the generator such that when the car was not running, the relay contacts would close and the starter could operate and when the car was running, the relay would not be able to ground and the starter would not operate.

The wiring diagram for this feature on a 1958 Buick is shown below - the key part of this diagram is where the ground side of the relay coil (terminal #4) is wired to the "armature" wire from the generator where is connects to the regulator. This is what we need to replicate after the car is converted to an alternator if we expect this feature to still function properly. The rest of the starter wiring should remain intact and functional.

 

In the modified wiring diagram below, there are two tricks, both very important. The first is to hook the relay coil ground wire (terminal #4) up to the proper connection on the alternator. The second is to use a diode in the system to prevent "feedback" and ensure that the car will cease to run when you turn the key off - the diode prevents power from the alternator from flowing backwards through the starter circuit and providing power to the coil - without it, the car will never turn off unless you unplug the alternator, the car runs out of gas, or the engine happens to stall. The key is to get the diode installed in the right place and pointing the right way - it's a one-way valve for electricity, so direction is very important!

Note that earlier versions of this diagram did not show the wire from terminal #2 on the alternator being connected directly to the junction block - they showed it connected to the main output wire in the middle of the harness. This change is to make sure the remote voltage sensing feature of the alternator works correctly. A small, but important, change.

NOTE: This is the part I'm not sure on - the exact details. The diode should go into the warning light circuit to prevent feedback - it should only allow electricity to flow from the warning light/resistor wire under the dash into the alternator. This circuit is also used as the ground for the relay coil - the warning light functions in much the same way as you want the relay coil to - on when the engine is not running, off when the engine is running. If you have looked at my Alternator Conversions pages, some of this should look familiar.

I am unclear if the diode needs to go into the combined branch for the #1 terminal on the alternator, or just into the warning light/resistor wire section of the wiring - I have shown it in the former position for now because I think that is the correct one. In this position, all power on terminal #1 at the alternator goes through the diode, thus preventing any power from the alternator from feeding back into the ignition system. Since the starter relay and the indicator light both get power at the same time from the same circuit (and are disconnected at the same time), they should not have any problems feeding back from one into the other.

Also, the relay coil itself may act as enough of a current draw to eliminate the need for the separate charging resistor in the wiring - I will have to try it out both ways to see what works best. I will update this page and the wiring diagrams as I learn more about this.

This diagram mixes and matches what is under the hood with what is under the dash. To be clear, most of this is under the hood - only the charge indicator (amp gauge), ignition switch, indicator light and resistor, and the neutral safety switch are under the dash.

  • The ugliest issue is that you will need to run one new wire from under the dash out into the engine compartment for the connection to the #2 terminal on the alternator. This has to be done for the alternator conversion anyway and is not specific to the starter wiring. In my case, the 1958 Buick has one unused wire slot in the factory firewall connector, so I'll be trying to use that in my case. You may not be so lucky and may end up running a new wire through the firewall - if so, use a connector and be sure to put some kind of rubber grommet on it where is goes through the firewall to prevent chafing. That's a very important detail - so don't skip it!

  • Next is that you will need to run the wiring for the indicator light and 10 ohm resistor under the dash, as well as mount the indicator light somehow. Again, this has to be done for the alternator conversion anyway and is not specific to the starter wiring. You will need to procure the resistor from somewhere - Radio Shack or another electronics supply store will be your best bet here. Get a resistor that can handle the power requirements - about 1 amp capacity will be sufficient, but remember that the resistor may get hot in operation, so mount it accordingly.

  • You will need to install the diode inline in the wiring harness somewhere in the engine compartment. You can carefully solder wires to each lead on the diode and put the entire thing inside heat-shrink tubing to keep it safe. It will be slightly bulky, but once you wrap up the harness, it will blend in nicely. Just be sure not to bend the harness too harshly right where the diode ends up at and don't use too much heat when soldering wires to the diode. Be sure to get the wire with the diode installed in the wiring harness in the correct direction - this could be easy to lose track of during all that soldering and harness assembly... Again, someplace like Radio Shack should be a good source for the diode you need.

  • You will need to hook the three wires together for terminal #2 on the alternator somehow. The wire coming out from under the dash and through the firewall will be from the indicator light and 10 ohm resistor. You will need to join that to the wire from the #4 terminal on the starter relay and the wire coming from the #2 terminal on the alternator that has the diode in it. My plan for the work on my 1958 Buick is to run both the indicator light and wire from the #2 terminal on the alternator to the #4 terminal on the relay and connect them together right there. In my case, the #4 terminal on the relay is a screw connection with flat-spade terminals on the wires, so I could easily put two spade terminals under the screw on the #4 terminal for a neat and clean approach. Keep in mind that if this connection ends up with a high resistance, the charging system could get confused and do funky things...


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Page last updated 01/02/2009 01:51:39 PM