Starter motor wiring help

[dirtbike]

Good day guys,

I need some help.

I recently removed all the wiring from the truck to tidy it up and get some non working items working again. All is going well unit I got to reconnecting the starter motor.

I have a 1965 F100 still using original wiring besides a few relays that I have now added for horn, headlights and thermo fans.

There are three wires from the wiring loom red/blue , brown and black/yellow going towards the starter motor.

I currently have the black/yellow connected up with the main cable coming from + battery terminal to one side of the solenoid.

I have tried connecting the red/blue and brown to the other side of the solenoid on the starter. When I turn the key the starter motor spins but does not engage. I measured the voltage while the ignition is in start position and I only get 8.9v where on the main cable coming direct from battery I am getting 12.4v.

Do the red/blue and brown wires both go on the same terminal on the starter solenoid?

Any suggestions?

[Roger Carter]

The blue/red wire should go to the "S" terminal on the solenoid and the brown wire to the "I" terminal. If there is only one black/yellow wire it would go to the Bat + side of the solenoid.

The blue/red wire is the "trigger" wire for the solenoid, that is, "hot" when the key is in the "start" position. If your truck has an auto trans this blue/red wire also runs through the neutral safety switch.
The brown wire is the ignition bypass. This bypasses the ignition resistor wire to supply full battery voltage to the ignition when the engine is cranking.

If you are getting the 8.9 v reading across the solenoid you should replace the solenoid, due to excessive internal resistance.

Hope this helps.

[dirtbike]

Thanks Roger.

Unfortunately there is no "S" or "I" terminals marked on the starter motor.

I think it is time to replace it with a fresh one!

[F7BIGJOB]

Thanks Roger.

Unfortunately there is no "S" or "I" terminals marked on the starter motor.

I think it is time to replace it with a fresh one!

The 'S' or 'I' is on the solenoid on the firewall.

[dirtbike]

The solenoid is on the starter motor, I replaced the original 300 engine with a 351C about 10 years ago.

[F7BIGJOB]

The solenoid is on the starter motor, I replaced the original 300 engine with a 351C about 10 years ago.

Understood-sorry

[dirtbike]

The solenoid is on the starter motor, I replaced the original 300 engine with a 351C about 10 years ago.

Understood-sorry

[Toyz]

If in fact just using the solenoid at the starter ( without an additional one one the fender), black/yellow should be your power to the ignition switch, and from your description, and the fact it energizes the solenoid, that part seems correct. The blue/red wire should go to the small terminal on the solenoid. often to the left of the larger battery terminal, with the brown wire attached to the other small terminal. I suspect that you have those two smaller wires reversed, thus the feedback from the coil feed thru the resistor wire is giving you the 8.9 volt reading. For diagnosis, leave the brown wire dis-connected, hook the blue/red to one terminal and try it. If it works, go ahead and hook the brown to the opposite terminal. If that doesn't work, reverse the two smaller wires, and you should be in business. It's quite possible I'm missing some key info here, so if this procedure does not work, just reply!
Paul

[dirtbike]

Thanks for all the input guys.

I pulled the starter motor out and had a decent look at it. It is still the original Bosch starter motor. I must have broken the connector sometime on the point marked 'SW' 1 on the photo. I managed to repair it. Popped the starter motor back in and she now engages and turns the motor over. I cant start it just yet as I am in the process of relocating the fuel tank from inside the cab.
So i'm still not sure where the Brown wire must go, from what I can tell it supplies 12v to ignition coil. So would I put it on number '4'? I have the positive cable, alternator and black/yellow attached to point number '3'.

[Toyz]

You could put it on #4, possibly with no ill effects. The other side of the coin is that it may tend to keep the starter energized due to continuous feed from the normal resisted ignition circuit. If you were to probe what appears to be a lug at #2, I believe you will find it is hot when the starter is engaged, thus, the correct location for the ignition starting bypass. I don't know what the availability of the solenoid is in your location, but it looks as if you might be a good candidate for such if available. If solenoids are not readily available, and it is proven that the coil needs full available voltage to easily fire the engine; a temporary "rig" would be a wire from battery to coil with a momentary switch to be engaged while starting.Another "fix" would be the use of a diode in the brown wire to allow flow only toward the coil. Running it from the #4 terminal may appear problem free, and could remain so, but well fits Mr. Murphy's premise that if it can go wrong, it will, and often at the most inopportune time!
Paul

[dirtbike]

Thanks Paul.
I sorted something out to get fuel to the carb and it turns out the engine starts and runs with the brown wire disconnected. Now I am really confused!

[Toyz]

Not really, one of two situations exist. Since you noted lower voltage at that point earlier, the logical answer is that the car will in fact crank off at the reduced voltage afforded by the resistance wire. This is not unusual with a good fresh tune and the absence of temperature extremes coupled with a good battery so coil voltage doesn't drop waaay down with the starter load. The other possibility is a back-feed from a full battery voltage source, which IMO, is unlikely in your case. I wouldn't recommend this as a long term solution, but may well work until inclement conditions exist. The good news is that if you note a reluctance to start, you can always jumper from a full battery voltage source to the positive side of coil to start. Just be sure to remove that jumper for two reasons. First, it WILL burn up points and probably coil; second, shutting the key off with it jumpered will not kill the engine, a somewhat bad situation in an emergency. Glad it's working; I would really plan on replacing that solenoid! Just be certain that brown wired is taped up and secured in the interim; if it touches ground, you are likely going no further.
Paul