I've been searching for a while but can't come up with a definite answer. I have a 1988 E350 RV, dual batteries (one starting, one "house"). I installed an isolator yesterday, correctly from the posts I've read, but turning the key the RV is dead. If I take the A post cable off (alt) and put it on post 1 (bypassing the isolator effectively), it works fine. I've seen some isolators with an "exciter" post....what's that? Do I need that type instead of the 3 post I have? The alternator has a BAT post on it, and a plug with 2 wires going into it, OR/BL and W/BK I believe. Any advice???

 

Sounds to me like you bought the wrong isolator. I have worked on several and the Fords all needed the isolator with the exciter (ignition) terminal.

 

Perfect thanks for the reply! I'll let you know how it goes.

 

Ok, got the isolator with the exciter terminal, wired it up to 12v with ign on, and same thing...nothing on the key. Just like the battery isn't even in the truck! I'm doing something very wrong obviously, but I can't figure it out? Any ideas?

 

Okay, you removed an isolator and should be installing the same thing you removed. What is different? This is normally a plug and play exchange.

 

I believe you must be hooking up the wrong wires. The isolator gets hooked up to the charge wire of the alternator. In other words, the original charge wire for the RV is cut, and the isolator is inserted in this wire. That takes care of 2 terminals on the isolator. The left over terminal gets hooked to the auxiliary battery charge wire.

Since you are killing the whole vehicle, I think you are splicing the isolator into the wrong spot in the wiring. If anything went wrong with your hook-up, it should affect the charging of the rv and nothing else.

 

Thanks for the replies! I haven't had a chance to get back to it, but wanted to clarify: I'm installing an isolator where there was not one before. The wiring was mucked with numerous times it's easy to tell. I removed a solenoid that was half cooked. Actually cracked from the heat.

Here's what I've got so far: the deep cycle battery hooked up to the "house" does work...all the lights etc come on. Also, the RV starts up fine on it's own battery and the alt charges fine. So I hooked the BAT wire from the alt to the A post on the isolator, the cable from the solenoid to the 1 terminal (that solenoid terminal is shared with a cable that goes to the battery), and the positive post of the house battery to the 2 terminal on the isolator. I got nothing on the key, like there is no battery in it. Swapped out the isolator for one with an exciter terminal, wired it to a known 12v "key on" source, and same thing. Nothing.

There are two other wires that plug into the alt (mentioned in my first post). Does one or both of those need to be "involved" lol? I'm a bit lost but am hoping one of you experienced guys can shed some light Any questions to help clarify, please ask!

 

Sounds to me like it should be...

Post A: Charge wire from Alt.

Post 1: 4ga or larger wire DIRECTLY to battery Positive (or you could hook up to the "hot" side of the solenoid)

Post 2: 4ga or larger wire to the "house" battery Positive terminal

Is this how you have it wired?

It sounds like this is how you have it. There's no reason for it not to work like this, the vehicle should run fine with no alternator at all for a little while if the main battery is good.

Kinda like this...

 

"the cable from the solenoid to the 1 terminal (that solenoid terminal is shared with a cable that goes to the battery)"

So if I read correctly you disconnected the solenoid? Is this the starter solenoid or one someone attempted to use to charge the Aux battery?

The above diagram where it shows to vehicle ignition system, Lights, etc is the primary wire on most Ford chassis that goes to the Start Solenoid. If you disconnect that wire you in essence disconnected the main battery to the entire vehicle. I would recommend you go into a parts store and buy a cable with fittings to add to that Starter Solenoid connection and run it to the isolator.

Replace the cooked solenoid ( If Starter)and Add the wire mentioned above. You should be good to go. Remember for an alternator to function it must have battery voltage supplied to the terminal. Make sure you have 12v on it. you may have blown the fuse link.

 

This is a good point that I had forgotten, however this will not cause a "no-start" if your battery is charged. Like Gumbyagain said, It seems the issue is somewhere in the battery and the solenoid wiring. I'm running on the assumption that this has the old style fender mounted starter solenoid like my 86 does.

Your known 12v run source isn't the run lead that engages the starter solenoid is it?

 

as i think about this problem, i remember that when i was doing a 3g conversion in my 87 and went to remove the original charge wires, i found them intermingled with other critical circuits on the vehicle.
for the sake of testing, simply move the wire thats currently on terminal A to terminal 1. if that allows the van to start and work normally, then i fully understand your problem.
if this is the case, your alternator wire shares a fusible link with all manner of other circuits, including those needed to start the engine.
if this is your case, you can solve the problem by moving the alternator output wire back to the starter solenoid where it originally was, and then adding an additional charge wire from the alternator to the A terminal of the isolater.

as i keep thinking about this, your old "isolater" was simply a solenoid (large relay) - and it cooked from heat. i would suspect that a previous owner made the mistake of using a starter solenoid in this position - starter solenoids are only allowed to be turned on about 50% of the time, otherwise they overheat. you could ask your parts store for a continuous-duty relay that looks like a starter solenoid, and install it just like you found the fried one.

or, you could be a real bad-azz like me and just add a second alternator and isolate your systems that way

 

He can't add a "additional" charge wire and keep the original charge wire hooked up. The old charge wire would be a pathway around the isolator. Current from the vehicle battery would flow down the old charge wire to the alternator, and then back to the isolator, through the diode in the isolator, and then down to the rv battery and drain the vehicle battery.

He needs to cut this original charge wire, the correct place is the problem. Probably the easiest would be to take the original charge wire off the back of the alternator and tape it up. Then run a new charge wire to the isolator from the alternator output terminal, and the from the isolator to the battery + or the solenoid battery +.

 

good point - my mistake. looks like connecting as close as possible to the alternator would be his best bet, but bypassing all the factory charge wires means that his ammeter (if it has one) will be bypassed as well. maybe it would be best to run a wire from alternator to post A, and from post 1 back to the vehicle side of the alternator's harness so that the flow of power is as close as possible to original, thus keeping the ammeter working.

 

It's hard to say with the vans, they get a little bit behind the trucks sometimes, but by 88 the trucks had a voltmeter. If his van has a voltmeter it should still work. If he has the old ammeter, I would not worry about it anyway, they never worked very well.

 

my 87 van came with an ammeter, so i'm guessing his 88 did as well. my 87 also has glass fuses and other old-style design details like that - they were just a few years behind, thats why vans kept the 70s body style up into the early 90s