Hello! I'm converting mech. FP to electric. Also, the choke will be electric instead of heat pipe system. Starter will be Powermaster 2-pole instead of orig. 3-pole. For these reasons, I need to find a good source of switched +12V from Ign. key. Likely so that it will stay hot during start. Any good advice where to take this signal, it probably can be found in the engine side of the wirewall? The other needed thing will be +12V start signal, but finding that is no problem.
All wiring info are welcomed!

 

There are a few ways to do it. You can use a diode, a 30A relay, or a Ford solenoid. I use a Ford solenoid to fire your starter and provide coil+ during start.

 

I have heard/read about using Ford-solenoid. You have then two solenoids; Ford one controlling the orig. one. Original one will be normally cold wired exept when starting. What do you benefit from that? Or is it just the Ford one providing the extra terminal that powermaster don't have?


What wire would you use to control fuel pump relay? Ballist. resistor wire or some other?

 

The Ford solenoid is a band-aid to overcome excessive resistance in the stock starter wiring circuit. As you correctly point out, the stock GM solenoid STILL needs to make contact to get the starter to work.

 

The Ford solenoid is used because the ministarter only has an S terminal and no resistance wire bypass connection. As an added benefit , it helps to prevent hotstart issues.

I would not use the resistance wire to fire your fuel pump. I would use a separate keyed source and a 30A relay similar to this.

 

For safety, you really should run the fuel pump through an oil pressure switch. There are a lot of factory installations that use this and a lot of available switches. These switches all have three terminals, one power in, one NC that powers the pump while cranking, and one NO that powers the pump when there is oil pressure.

 

I understand the use of Ford solenoid to provide the res.wire bypass terminal. More simple way seems to be the diode wire or even a relay controlled with starter "S"-terminal. I'll vote for diode because of no moving parts.
I might be stupid, but I don't understand how it helps hot starting. The original GM solenoid still has to work to get the car started! It is not much of a help if the extra solenoid is out of the headers heat.

 

Joe, are those oil pressure operated safety switches really capable to handle the fuel pumps current without a relay?

 

That was the original factory application of that switch.

The heat causes increased resistance in the GM solenoid coil and contacts. When coupled with a contact disk that is pitted from age, and NSS terminals that are dirty from the grease inside the switch, voltage in the stock starter circuit drops to the point that the GM solenoid won't engage. The external relay (Ford or otherwise) bypasses the resistance drop in the starter circuit wiring to the NSS and ignition switch, applying battery power directly to the GM solenoid. This is enough of an improvement in the voltage drop that it can overcome the heat-induced resistance and the pitted contacts.

Of course, a fresh set of contacts in the GM solenoid and clean terminals in the NSS/start circuit do the same thing.

 

Thanks Joe, I'll do the search for suitable safety switch. Kind of like the idea that relay is not needed. I like to keep things as simple as possible.




About the Ford solenoid, I got it now and agree, it's more like band aid.