The starter solenoid just quit on my flathead. It has 2 large terminals (1 connected to battery, one to starter) and one small terminal that connects to the ignition switch. No numbers on it but it looks like a Borg Warner Division S79. Plan to get another tomorrow. Just wondering why do some solenoids have 2 large terminals and 2 small terminals? What is the second small terminal, a ground? Posted using the Full Custom H.A.M.B. App!
I just bought a 4 post (two big posts and 2 little posts) 12volt starter solenoid for a 60's ford truck at the auto parts store to replace my 3 post (two big ,one little post) 6 volt one on my 49 Plymouth since it took a **** a few days ago and since im converting to 12 volt and it came with a instruction paper in the box that says just dont use "post B" (one of the little posts) if your vehicle is a 3 wire setup. if your running 12 volt you could use the same thing the 60's ford solenoid was $10 nice and cheap!
Two different ford solenoids are also dependent on your type of starter switch. One is activated by ground the other is the positive hot wire. Most of the push ****on activated types located on the dash are ground activated. Be sure you buy what you need.
The 6V solenoids on a Ford have a hidden connection inside. The starter ****on grounds the solenoid from the small terminal which completes the hidden circuit inside the solenoid energizing the solenoid. There is a battery side and a starter side. The 12V type has 4 terminals . One of the small terminals needs 12V supplied to it to energize the solenoid.
The 4 post solenoids were used on Ford point-type ignitions to allow full 12 V to the coil while starting, byp***ing the ballast resistor, the purpose of the second small (byp***) terminal. The 3 post solenoids came about in the early '70s with point-less electronic ignitions that do not use voltage dropping coil resisters, but run 12 V full time.
So here's the whole story: I'm running a 52' flathead. I have converted it to 12 volt, negative ground. I have a 12V GM alternator. It has a Mallory Dual Point Distributor with Mallory balast resistor. I am using a modern type ignition switch that sends positive to the solenoid. Started and ran fine before. Old 3 post starter solenoid quit (probably because i dropped it on the floor when cleaning it up before remounting it). I just purchased a BWD S603 - 4 post solenoid. Instructions in the box say: "Installation Instructions for Dual Battery Switch" Directions say connect: 2 large posts should connect with 10 ga. to each battery. One small post to 16 ga. ground and one small post to 16 ga. accessory on ign. switch. Not sure this is what i want?
What you have is a constant duty solenoid, the one you want is whats commonly known as a Ford solenoid,although the parts man may have to have a little gray hair to know that, it will be for intermitent duty. The one you have should be able to be used on your system. Now news to me I didn't know the 4th post was the resistor byp*** the ones I've used in the past that went to ground
Yes it makes sense from the directions that this is a constant duty type. For "resistor by-p*** type" the 4th small terminal would have to be hot (+) only when the key is in the start position. The one i purchased says connect 4th small post to ground (-). If i connect it to the resistor byp*** it might result in FIRE! There are obviuosly different types as others mentioned above.
Going back to parts store, will let you know. Kid helped me at Advance Auto this morning. Going to the good old Napa where the old timers are this time.
Right on V8 Bob. Went to Napa and got a ST81. This is Ford type, with 1 battery terminal (+ from battery), 1 starter terminal (+ to starter), 1 ignition terminal (12v to coil) , 1 starter switch terminal (12v from ignition switch). This way I can boost the starting voltage to coil if I wanted to in the future. Also Learned the continuous duty solenoids have metal bodies. The BWD S603 continuous duty would have worked as Vimtage Iron said but does not allow 12V coil boost feature. Hooking it back up 3 wire for now since it was working fine. Thanks again to everybody! By the way - Napa guy walked right to the shelf, didn't even need to look up the part.
The Jalopy Journal
