Fuel Selector Valve on a 1984 and Bosch Relays

Well, spent a few minutes under the truck and it would seem that I found one wire that has power when the front tank is selected and no power when the rear is selected.

I gather that this is possible from a few folks including Agnem. Now here is the weird part. The wire bundle has 8 wires. I cannot see past the FSV because of the skid plate and the way it's mounted, but I assume two of the wires in the bundle go to the rear tank's sender, leaving 6 wires - and maybe one is the ground for the FSV? Leaving 5 others?

In any case I'm wondering if I can wire my Bosch relay in reverse somehow to activate my 12v fuel line heater when there is no power to a contact?

Not electrically inclined and I'm muddling my way through this so any help on figuring out how to get the relay to work in reverse would be greatly appreciated.

The issue being that the Pollack (I assume the OEM FSV is a Pollack 6 port) is provided 12v + when on the front tank (my diesel tank who's fuel I do not want heated) and 12v - when the rear (WVO/WMO) tank is selected which I **DO** want the heater on for.

maybe not the answer you are looking for but couldn't you piggy back at the fuel switch itself?

what do you mean "piggy back"? presumably the switch only transmits 12v + when in the "front tank" position. I need 87 to provide 12v+ to my heater.

There has to be a way to get the relay to work in reverse. Meaning provide 12v+ on 87 when the 86 is 12v-

Ok I think I got this. Damn I should have been an EE not a CS guy:

#30 to +12vdc from battery via circuit breaker (I have one)

#85 to +12vdc from battery via circuit breaker

#86 to my "switch" wire which is -12vdc when I want power to #87 (my +12vdc output to the Vegtherm)

#87 to +12vdc side of my Vegtherm.

negative side of vegtherm to a chassis ground.

mankypro said:

Ok I think I got this. Damn I should have been an EE not a CS guy:

#30 to +12vdc from battery via circuit breaker (I have one)

#85 to +12vdc from battery via circuit breaker

#86 to my "switch" wire which is -12vdc when I want power to #87 (my +12vdc output to the Vegtherm)

#87 to +12vdc side of my Vegtherm.

negative side of vegtherm to a chassis ground.

Click to expand...

#30 to fuse to battery +
#85 to switch to turn on vegtherm (power from fuse box with fuse tap) It's better to tap a fuse that's off when the truck is off. That way your vegtherm will NEVER be on if you forget to turn it off. That's why using the battery here is not the best.
#86 to chassis ground
#87 vegtherm power
negative vegtherm to chassis ground

http://www.classictruckshop.com/clubs/earlyburbs/projects/bosch/foglites.htm

Good point. Only change I'd make would be to put #85 on a fused accessory line thats on when the truck is on. I think everything else stays the same.

#30 to +12vdc from battery via circuit breaker (I have one)

#85 to +12vdc from battery via fused accessory tap that is off when ignition is in off position.

#86 to my "switch" wire which is -12vdc when I want power to #87 (my +12vdc output to the Vegtherm)

#87 to +12vdc side of my Vegtherm.

negative side of vegtherm to a chassis ground.

hheynow said:

#30 to fuse to battery +
#85 to switch to turn on vegtherm (power from fuse box with fuse tap) It's better to tap a fuse that's off when the truck is off. That way your vegtherm will NEVER be on if you forget to turn it off. That's why using the battery here is not the best.http://www.classictruckshop.com/clubs/earlyburbs/projects/bosch/foglites.htm

Click to expand...

mankypro said:

#86 to my "switch" wire which is -12vdc when I want power to #87 (my +12vdc output to the Vegtherm)

Click to expand...

#86 is relay ground !!!

What I'm doing is reversing the circuit function - or at least attempting to. Remember my connection to #86 is the wire that is -12vdc when my WMO tank is on.

hheynow said:

#86 is relay ground !!!

Click to expand...

OK design proven. It works the way I detailed in post #6. Hey sometimes walking on the wild side pays off. It's 8:24pm here right now and I'm headed to get some 30a fuses for the accessory wire - but it works! Yeehaw.

Pictures of the whole thing in the a.m. pictures taken in darkness with a flash suck anyway. I believe the wire which switches is green - will verify in this post.

Good deal but I was expecting an explosion.

hheynow said:

Good deal but I was expecting an explosion.

Click to expand...

Sorry it didn't blow up

If you read the notes from Bosch on the original relay:

http://www.dlcparts.com/images/BoschGuide.pdf

They talk about reversing the inputs briefly and say it's perfectly safe to do. Reading that document (RTFM) I also learned of myriad cool things you can do with these relays - like increase the brightness of one's headlight system, make engine cutoff switches, etc.