So I have the factory dual battery setup. Everything appears to be right, nothing hobnobbled to gether. So I finally got 2 new batterys and hooked up but it,s only charging 1 battery. Anyone have a wireing diagram so I can figure this out. Thanks.

 

Is the auxiliary battery the one that's not charging? If yes, then the first thing I would check is the aux. battery solenoid switch. Make sure it's closing when the ignition is "on".
The diagram shows there's a 7½ amp fuse in the control circuit, I'd start there.
Here's the wiring diagram

 

I have the same setup check the aux battery relay... I also recommend getting a smart relay for the aux battery. The issue with the stock setup is on run both batteries are connected, so if your start battery or aux battery goes bad the other battery tries to compensate. With a "Smart" relay the aux battery does not get charged until the start battery is recharged. With a smart relay you can also jump your start battery using a momentary over-ride switch, just make sure to use 4 gauge wire between relays.

 

Even though it looks the same, the dual battery solenoid is not the same as a starter solenoid (aka starter relay).

E5TZ-14677-A (replaced D3TZ-14677-A & B) .. Dual Battery Solenoid / Obsolete ~ 70+ available NOS

1973/89 F100/350 / 1975/89 Econoline.

 

Yup. The starter solenoid is designed for momentary use, the "accessory relay" is designed for constant use (100% duty cycle).

 

There is a fusible link in the aux battery charging circuit, Check to see if it has blown. The link comes off the (+) terminal of the starter solenoid and is shown in the above wiring diagram.

A note of caution. The previous owner of my '78 had winch on the truck, powered off the aux battery. He told me he had had problems with the aux battery charging ever since installing the winch. Found out he had kept the engine running while winching.
While the engine is running both batteries are connected only by the above mentioned fusible link. The load of the winch, when in use, took out the fusible link.

The aux battery system was designed to power a camper or trailer and isolate the primary battery when the truck wasn't running. Once the truck starts, the charging system charges the aux battery through the fusible link and aux battery relay.

Good luck.

 

Thanks everyone, it look like my mechanical error from when I put the clip back on 2 winters ago. I had a wire where it shouldn't be. I will keep you up to date.

 

So this pic is a junction boas I call it) just behind the booster. The power comes to it from the main starter sol, then drops down to the aux sol. I am not sure which side the wires go to. The aux battery+ cable goes to the side closest to the battery. Thanks, I,m sure this is simpler than me.LOL.

 

From the terminal you should have a fusible link that connects to the opposite side of the solenoid, I will take pics of my setup in about 15 min and post. My setup is stock so it should give you a good idea. Standby for pics

** The 73 wiring diagram above looks to be a miss print as the AUX (+) battery lead should be on the other side to effectively isolate the batteries when the ignition is turned off.

 

Thanks. I had the link connected to the side closest to the firewall. But I think you are right. I have not gone out to switch it yet.

 

See below



From the terminal is a black fusible link



Black/Yellow wire with green fusible link goes to the terminal from the starter relay


Original 100% duty cycle solenoid, still works after 40 years (Ford Tough)

 

Thank a lot. My sol has 2 small terminals on it. Yours has 1, maybe that's my problem.

 

Mine is original and grounds off of the body. Two terminal switches have an extra terminal to ground, make sure your solenoid is 100% duty cycle otherwise it will eventually fail. Also the original wiring isnt designed for high amp loads, ie; it cannot self jump, so if I'm not mistaken the original solenoid is only rated at 60 amps (NumbersDummy will correct me shortly LOL).

 

The line from the terminal block and the (+) cable from the aux battery connect to the opposite sides of the aux relay, as F250 Super 4X4 says. Doesn't matter which side, just as long as they are on opposite sides. If your solenoid has two small terminals on it it sounds like it is a starter relay (momentary contact). The constant duty relay would have one terminal, energized from an ignition on lead.

 

Ok, so I need a single terminal sol then. We have a napa store close by, is there a specific part# that I need?