73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Electrical => Topic started by: Takilma on March 15, 2015, 09:46:56 PM
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So in case anyone finds their dashboard tank switch to be DOA (see picture for example of switch) it can be replaced with an ordinary "double pole, double throw, MOMENTARY" switch. Examination of the OEM switch reveals that all it does is connect the pink wires to the green wires in one direction (left hand tank) and reverses "polarity" on the same connection in the other direction (right hand tank). Connect pink wires to center pins of DPDT switch, green wires to one pair of "outboard" pins. Make "jumper" wires from other set of "outboard" pins that connect to the pins with the green wires making sure that they CROSS over side to side. Most of you are probably laughing at this simple post, but hey, I had to noodle this up for myself and maybe someone out there is also scratching their cabeza. One more thing, I had to make a cover plate to mount the toggle switch and cover the rectangular hole in the dash, so not for the show crowd...
this whole deal is just to save bucks.
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some pictures might help. i just took mine apart a couple months ago and im confused on what your saying. i understand how the stock one works but idk what youre talking about. maybe im just tired lol
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Irish,
Here's a rudimentary drawing. If you find it more confusing than helpful, let me know and I'll try to make a better one...
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last I knew there was repops being made of these, I bought one a few years back.
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last I knew there was repops being made of these, I bought one a few years back.
Standard Ignition makes the momentary version p/n# DS293 for 81-88, and DS455 for 75-80. For the one that isn't momentary, like my 87, the A/C Delco p/n # is D7089C.
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thats how the stock one right? i understand how that works but im just not sure about what youre talking about. got any info on the switch youre talking about?
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These switches are nothing more than a DPDT switch which you can pick up in any electronics store. The only thing that makes them unique is the bezel around it.
(http://cdo.seymourduncan.com/blog/wp-content/uploads/DPDT-on-on.png)
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lol ok now i understand. before your first picture looks pretty much how the stock one works thats what confused me.
but do you have a ideal how to make this work with the 75-80 style they have 5 wires
(http://contentinfo.autozone.com/znetcs/additional-prod-images/en/US/wl2/SW412/2/image/3/)
i dont know anything about them.
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Irish,
I see you are dealing with a "whole 'nuther" switch than I have. You can still work up a replacement. Use an ohm meter or a battery powered test light and "map" out your switch. I realize that since your switch is probably bad, you won't be able to get connection on all pins/positions but try holding the switch on real hard, maybe some contact cleaner sprayed in it will help it. You will find it either is a conventional switch like enaberif's diagram...or it is doing a "tricky" crossover thing like Takilma's drawings. Either way, a "garden variety" switch will do the job.
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Here's a pretty good set of wiring diagrams courtesy of CaptKaos buried in this very forum.
Unfortunately, looking through them, I see nothing about dual tank switches...
http://forum.73-87chevytrucks.com/smforum/index.php/topic,11766.0.html
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lol no i have the first one you posted. i dont know anything about the other style just knew they had a couple different styles
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found this courtesy of hatzie
(http://johnnynightstick.s3.amazonaws.com/IMAGES/73-80%20tank%20switch.jpg) (http://forum.73-87chevytrucks.com/smforum/index.php?topic=29531.msg247201#msg247201)
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^^^^ That's the 73-80 5 contact rocker switch.
It's just a Double-Pole Double-Throw ON-ON rocker switch that's missing one terminal to key the connector so it can't be plugged in backwards. The single terminal solenoid valve is only energized when the switch selects the AUX tank so the 6th terminal is not needed. The 73-80 tank switch also switches the gauge directly at the dash. You can use an ON-ON DPDT Toggle switch rather than the GM rocker by cutting off the 6th terminal.
81-91 motorized valve system...
I'm not sure why GM chose to use a three position Momentary-OFF-Momentary Double-Pole Double Throw Polarity reversing switch on the 81-86 trucks. The 12VDC motor driven Pollack valve has an internal limit microswitch and diode arrangement that shuts the motor off once the valve shuttle reaches the end of its' travel. The 87-91 RV series trucks use the AC Delco D7089C two position ON-ON DPDT polarity reversing switch. When the Momentary style switch fails... you can and should pitch the 81-86 style switch in the bin and use the 87-91 style switch on the 81-86 trucks.
The 81-91 Pollack valve handles the gauge select function with a second microswitch internal to the valve.
Attached is a drawing that shows the function of the valve and two position DPDT Polarity Reversing ON-ON switch. I left out the OFF resting position of the 81-86 switch.
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This is a graphic of the internal function of both switch styles.
The LH pane is the Polarity reversing switch the RH pane is the 73-80 DPDT 5 terminal switch.
I'm trying to demystify the internal workings of the dual tank systems a bit...
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Here's a pretty good set of wiring diagrams courtesy of CaptKaos buried in this very forum.
Unfortunately, looking through them, I see nothing about dual tank switches...
http://forum.73-87chevytrucks.com/smforum/index.php/topic,11766.0.html
Those are Haynes or similar one-size-fits-all wiring diagrams. They're OK but they're missing a bunch of optional equipment wiring detail that's in the GM manuals.
Chris posted copies of the scans I made of the GM service manuals. They include year specific wiring diagrams that do include the RPO NL2 wiring diagrams for each year.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=25639.msg213706#msg213706 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=25639.msg213706#msg213706)
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Hatzie there is also a push/pull style that is very uncommon found in the 73-74 trucks possibly 75. Looks like a headlight switch.
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HATZIE, you should put all of this information into a post in the tech section. I will be looking for this info when I put my TBI back to working dual tanks.
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Hatzie,
Good stuff, thanx. I'm saving the link to the GM diagrams. I think you've pretty much put this topic to bed.
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Hatzie there is also a push/pull style that is very uncommon found in the 73-74 trucks possibly 75. Looks like a headlight switch.
There was a cable operated valve in the 73 & 74 trucks. Not much info on these in the service literature and parts are near non-existent. I believe the cable valve system had a completely separated dash mounted SPDT switch to route the senders to the gauge. The gauge didn't follow the enabled tank.
1980 had a time delay relay to keep the valve energized with the starter.
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HATZIE, you sh ok uld put all of this information into a post in the tech section. I will be looking for this info when I put my TBI back to working dual tanks.
TBI fuel pumps run off the same Green wires that run the valve. It's actually pretty clever that they didn't have to switch the fuel pumps any further. The fuel sender and fuel pump share a ground that runs through the liquid tight grommet in the sender to the frame along with the fuel pump power wire and sender wire that run to the valve.
They shut off the not selected fuel pump as follows... When the LH tank is selected the RH fuel pump has two grounds. When the RH tank is selected the LH fuel pump has two grounds. You need power and ground to run the fuel pump two grounds will just shut it off.
GM did a poor job of making the 1987 RV series wiring diagrams readable. They're very difficult to follow and not miss things... like the Hot-Start fuel pump relay system controlled by what passed for an ECM in 1987.
Look over the 1988 -1991 RV wiring diagrams but keep in mind they also seem to be missing the fuel pump relays... Maybe that's a 1987 only thing but I doubt it.
1987 TBI is where the MOTOR year-specific wiring diagrams shine. Pages from that manual, that include the hot start relay etc, are posted here... http://forum.73-87chevytrucks.com/smforum/index.php?topic=9072.msg198713#msg198713 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=9072.msg198713#msg198713)
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Yea that info will be needed when I get around to making both tanks work again.
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found this courtesy of hatzie
(http://johnnynightstick.s3.amazonaws.com/IMAGES/73-80%20tank%20switch.jpg) (http://forum.73-87chevytrucks.com/smforum/index.php?topic=29531.msg247201#msg247201)
Thank God for this layout as I'm going to need it RIGHT quick. Quick question regarding this... I should be able to ohm out the pins on the switch to get a reading from tank? Meaning if the sender is right in the tank then I should be able to get the 0-90 ohm reading correct?
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found this courtesy of hatzie
(http://johnnynightstick.s3.amazonaws.com/IMAGES/73-80%20tank%20switch.jpg) (http://forum.73-87chevytrucks.com/smforum/index.php?topic=29531.msg247201#msg247201)
Thank God for this layout as I'm going to need it RIGHT quick. Quick question regarding this... I should be able to ohm out the pins on the switch to get a reading from tank? Meaning if the sender is right in the tank then I should be able to get the 0-90 ohm reading correct?
You should be able to test the senders from the dash switch plug to a good ground.
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