# Converting Polarity using relays: 12+ to GND **URL:** \ **Category:** NYSpeed Off Topic\ **Created:** [April 12, 2013, 8:49am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943 "2013-04-12T08:49:10Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Norb\_O](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/norb_o/32/5189_2.png) [@Norb\_O](https://forums.speedlife.net/u/Norb_O)\ **Post date:** [April 12, 2013, 8:49am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943/1 "2013-04-12T08:49:10Z")
I’m retarded when it comes to electrons, so I figured I’d ask the electrical whizzes about a few things for wiring my car. (paging LUKE\_L?!) The fuel pump on my car (among a few other things) is trigged by a ground signal that comes from the OEM SPDT fuel pump relay. The GM PCM provides a handy fuel pump trigger signal, but it’s 12V+. I’d like to introduce a new SPDT relay into the system that converts the polarity of the signal provided by the GM PCM, and uses that new ground signal to energize the BMW SPDT relay, which then powers the fuel pump. I’m curious as to which spades on each relay need to be connected where. Physically all the wiring is being done in the electrical box that houses the ECU under the hood, so ground and key “on” 12V+ are both readily available. Both relays will be neatly mounted in that box. This whole exercise is actually being done twice (once to energize the stock fuel pump, and again separately to power up the DME relay which controls a shit ton of things). ---
**Author:** ![Haenszel](https://avatars.discourse-cdn.com/v4/letter/h/e68b1a/32.png) [@Haenszel](https://forums.speedlife.net/u/Haenszel)\ **Post date:** [April 12, 2013, 8:55am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943/2 "2013-04-12T08:55:24Z")
12v Pump trigger to 86, ground to 85, ground to 30, and 87 to fuel pump. ---
**Author:** ![Norb\_O](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/norb_o/32/5189_2.png) [@Norb\_O](https://forums.speedlife.net/u/Norb_O)\ **Post date:** [April 12, 2013, 8:58am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943/3 "2013-04-12T08:58:40Z")
can 85 and 30 go to the same ground on the body? ---
**Author:** ![Haenszel](https://avatars.discourse-cdn.com/v4/letter/h/e68b1a/32.png) [@Haenszel](https://forums.speedlife.net/u/Haenszel)\ **Post date:** [April 12, 2013, 9:00am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943/4 "2013-04-12T09:00:24Z")
Sure. Just make sure its solid. ---
**Author:** ![Norb\_O](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/norb_o/32/5189_2.png) [@Norb\_O](https://forums.speedlife.net/u/Norb_O)\ **Post date:** [April 12, 2013, 9:50am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943/5 "2013-04-12T09:50:55Z")
seems far too easy. thanks for the input. does it matter whether it’s a 5 pin ![http://pimg.tradeindia.com/01229021/b/1/Relay-Teclo-Type-5-Pin-12-24-Volt.jpg](http://pimg.tradeindia.com/01229021/b/1/Relay-Teclo-Type-5-Pin-12-24-Volt.jpg) or 4 pin ![http://www.mm-4x4.com/ekmps/shops/mm4x4/images/4-pin-30-amp-relay-2810-p.jpg](http://www.mm-4x4.com/ekmps/shops/mm4x4/images/4-pin-30-amp-relay-2810-p.jpg) i would assume the 4 pin is fine ---
**Author:** ![Haenszel](https://avatars.discourse-cdn.com/v4/letter/h/e68b1a/32.png) [@Haenszel](https://forums.speedlife.net/u/Haenszel)\ **Post date:** [April 12, 2013, 9:51am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943/6 "2013-04-12T09:51:45Z")
Nah, 5 pin (#87) is just an additional Normally Closed pin. You won’t be using that. ---
**Author:** ![Spam16v](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/spam16v/32/5287_2.png) [@Spam16v](https://forums.speedlife.net/u/Spam16v)\ **Post date:** [April 12, 2013, 11:22am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943/7 "2013-04-12T11:22:38Z")
5th pin is to get you bitches, bitches love the 5th pin. ---
**Author:** ![L8APEX1](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/l8apex1/32/7276_2.png) [@L8APEX1](https://forums.speedlife.net/u/L8APEX1)\ **Post date:** [April 12, 2013, 11:32am UTC](https://forums.speedlife.net/t/converting-polarity-using-relays-12-to-gnd/229943/8 "2013-04-12T11:32:15Z")
Either will work