Dual tanks not switching

[pontgta]

Actually disconnect the valve first and try to start the truck and see what you get. Then You can disconnect all the wires to the valve, connect 12 volts and ground to the green and light green wires then reverse polarity and it should switch. if it does not, then you have something wrong with the valve.... I would have Bench tested it before i put it on.. You should have at least heard or felt something.

[hatzie]

Originally Posted by Ol' Red

Ok this is where I currently am. I have the original valve on the truck. I took the new one back to advance because I didn't think that was the problem at the time. So I am getting the proper power to both green wires. 12v from lt green to dk green just as hatzie said. I cleaned and sanded both grounds off the senders. Today I bypassed the sender and went straight to ground. It still didn't work. I hooked. 12v battery to the motor terminals d and e. the way I did it was I had 1 regular wire going from positive to d. Then I had a wire with a test light on it going to e from the negative terminal. The motor didn't go however the light lit up showing I have continuity through the valve motor. I am wondering if just maybe the reason the new valve didn't work when I tried it was because my ground to the sending unit was bad. The last time it was on the right side the gauge was at 3 o'clock which I've heard it lack of ground. I have since cleaned that ground but have not tried a new valve since the . One other thing, for some reason I can hear a small click when I switch left but not right. I hope this is all making sense what I said.
Posted via Mobile Device

The ground to the valve is from the dash switch not the senders. You'll find a buss bar under the dash like the wiring diagram shows.

The senders are a separate circuit.

[78 Bonanza]

I had trouble with my 78 dually tank system for 13 years before I wised up and went with the old valve setup. It wasn't a hard project and it sure beats laying on the side of the highway in the winter with snow coming down and semis spraying slush and road salt in your face.
A year after I bought the truck I changed all of the wiring, switch, tank selector, fuel lines, the works. It lasted for three years of work and then started the same old garbage. The last time it quit on me I was pulling a really heavy load way out of town and it stopped on a two lane without an emergency lane. It was around 98 degrees that day and the truck just happened to stop on an ant hill. Bad day to say the least!
I can get the brass valves for the pre 73 model trucks for fairly cheap (not the $150 that the parts houses want) and can get them to you if you want to go that route. You will need two, one for the feed lines and one for the return lines. I put them just in front of the seat where all I have to do is reach down and turn the handles when the gauge is reading low. Really easy fix! Took me and my kids an afternoon to switch over the system. It was well worth it! The only thing the switch in the dash does now is to let me know how much fuel is in each tank. Hope this helps. Let me know if you are interested and I will get you a price quote with your address.

[chevy1ton]

Disregard the pink wires to the senders they are not used as ground for the valve as I thought, they are for the gauge only, I was wrong and did not mean to confuse you more.
Bench test your valve again, go back to your d and e terminals. As hatzie stated the 2 green wires switch polarity meaning when you hit your switch one acts as a power wire while the other acts as a ground completing the circuit and vice versa when switched to the opposite tank.
Put power to d and ground e, then switch your power to e and ground to d, if the valve is working properly you should hear it switch over.

[Ol' Red]

I tried finding the buss bar but am having troubles finding it. I know you said it was by the e brake but not entirely sure where it is.
Posted via Mobile Device

[dieseldawg142]

Originally Posted by Ol' Red

I tried finding the buss bar but am having troubles finding it. I know you said it was by the e brake but not entirely sure where it is.
Posted via Mobile Device

here you go, left side under the wire in the grommet

[hatzie]

Originally Posted by dieseldawg142

here you go, left side under the wire in the grommet

A couple extra grounds there.

[Ol' Red]

Today I had a chance to look at the truck again. The ground at the buss bar is good. I found out something pretty interesting though. At my switch I took my volt meter and get 12v from the pink to black. Power to ground. When I go pink to either green wire I only get 4v. I understand that whatever green isn't getting power the other is ground. I am jus trying to figure out why it would only be 4v. When I did this I had the switch off the connector. Any ideas?
Posted via Mobile Device

[hatzie]

Originally Posted by Ol' Red

Today I had a chance to look at the truck again. The ground at the buss bar is good. I found out something pretty interesting though. At my switch I took my volt meter and get 12v from the pink to black. Power to ground. When I go pink to either green wire I only get 4v. I understand that whatever green isn't getting power the other is ground. I am jus trying to figure out why it would only be 4v. When I did this I had the switch off the connector. Any ideas?
Posted via Mobile Device

With the switch unplugged the green wires are essentially free floating. They go through the motor in the valve but don't terminate anywhere. You shouldn't be getting any volts.

Either the valve is weakly conducting to a ground (the gauge circuit on Terminals A B C of the valve) or the wires have a weak short to ground via damaged insulation. My money would be on the valve itself...

1. Plug some male 1/4 disconnects into the green and black terminals of the dash switch plug so you don't damage the plug terminals with the meter probes.
2. Unplug the valve under the truck.
3. Set your meter to 1K OHMS and probe from the green wires to the black wire. You should see an open circuit (same as disconnected probes).
4. If you get a reading on one or both find where the insulation is worn away on the frame etc.
5. No reading? Replace the valve. It's shorted internally between the motor and gauge circuit.

[Ol' Red]

This is sort of an old thread but just wanted to let everyone know what the problem was. My switch, valve and wires all seemed to be working just fine. A new valve was the part that fixed it. The switch was. I did continuity checks on it and made sure i was getting the proper voltage to the valve which i was however just for fun I took some wires and used them in place of the switch and the valve worked just fine. I bought a new switch and it fixed it. I have no idea how the switch was bad even though it had the volts going through it but it was definitely bad.

[NASTY-LSX]

thanks for the update!

[hatzie]

Thanks for the update. The switch is the most common failure point. The valve is big bucks but the AC Delco # D7089C switch is cheap.
This part # is listed as 1987-91 RV series TBI only. It's an ON-ON switch, is easier to use, and will last longer than the "right" momentary switch. It works just fine for all 1981-1991 CK RV dual tank trucks.

[Chevy3+3]

Bringing this back from the dead to aid in helping fix my truck

[gmachinz]

The ON-ON switches are the ones to use. I'd dis-regard using the other ones too. I just built all new dual tank harnesses for my project and now have those fuel harnesses available so now at least people can swap out their entire 25+ year old wiring if need be.

[hatzie]

Originally Posted by gmachinz

The ON-ON switches are the ones to use. I'd die-regard using the other ones. I just built all new dual tank harnesses for my project and now have those fuel harnesses available so now at least people can swap out their entire 25+ year old wiring if need be.

He has an 88 TBI so that's already the right switch... but really it's the only one to use with the motor valves period. The intern engineer that thought the momentary switch was a good idea should be beaten senseless with wet spaghetti.