Cool 964 Test switch and Emergency DME Relay Replacement
Thread Starter
Rennlist Member
Joined: Jan 2014
Posts: 76
Likes: 5
From: San Diego CA
Cool 964 Test switch and Emergency DME Relay Replacement
I was doing some troubleshooting on my 1991 964, and I realized I needed a way to control the fuel pump and DME power independently from the fuse box without starting the car.
I came up with a simple tool that was extremely helpful for operating the fuel pump for testing the fuel pressure... without powering the DME. It uses a 3-position (ON-OFF-ON) double-pole, double-throw toggle switch ($3.99 Home Depot), a couple feet of wire, and some crimp-on connectors. It is plugged into the fuse box when the DME relay is removed (see photo). You can move the switch to the Pump position to power the fuel pump only for fuel pump pressure testing a various other issues; or move it to the Pump+DME position to power the fuel pump and DME (see photo). This position will get you home if the DME relay fails, so keep it in your glove box. Here are some photos of the completed switch and a wiring diagram showing how to wire the back of the switch. It took about 15 minutes to make. Have fun!
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Test your work with an ohmmeter before installing!!!
I came up with a simple tool that was extremely helpful for operating the fuel pump for testing the fuel pressure... without powering the DME. It uses a 3-position (ON-OFF-ON) double-pole, double-throw toggle switch ($3.99 Home Depot), a couple feet of wire, and some crimp-on connectors. It is plugged into the fuse box when the DME relay is removed (see photo). You can move the switch to the Pump position to power the fuel pump only for fuel pump pressure testing a various other issues; or move it to the Pump+DME position to power the fuel pump and DME (see photo). This position will get you home if the DME relay fails, so keep it in your glove box. Here are some photos of the completed switch and a wiring diagram showing how to wire the back of the switch. It took about 15 minutes to make. Have fun!
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[/IMG]Test your work with an ohmmeter before installing!!!
Rennlist Member
Joined: May 2006
Posts: 146
Likes: 1
From: Northeast NJ
nice idea, nice work, but I don't see why having a single male-male spade connector jumper wire, and a 'y' male-male-male jumper wouldn't do exactly the same thing.
a silver sharpie could be used to put a couple of notes on the fuse box to indicate how to insert the jumper when the relay fails. 30>87 & 87b jumps the DME and the fuel pump, and gets you running again.
a silver sharpie could be used to put a couple of notes on the fuse box to indicate how to insert the jumper when the relay fails. 30>87 & 87b jumps the DME and the fuel pump, and gets you running again.
Drifting
Joined: Aug 2002
Posts: 2,557
Likes: 14
From: Dallas, TX
Is that toggle isolated? There could be a bit of current thorough the circuit, don't want it reaching the end user.
I normally use a y cable jumper when I need to run the pump. Actually, you don't need the Y. Just one jump from the 12V source to the pump would do for testing the pump without powering up the DME.
I normally use a y cable jumper when I need to run the pump. Actually, you don't need the Y. Just one jump from the 12V source to the pump would do for testing the pump without powering up the DME.
Thread Starter
Rennlist Member
Joined: Jan 2014
Posts: 76
Likes: 5
From: San Diego CA
Jumpers and Y's do the same thing... this is just the geek in me wanting to add a cool and convenience factor. For the troubleshooting I was doing, it made it fast and easy, then tossed in the glove box for an emergency DME relay replacement if ever needed. And yes, I insulated the connectors with silicone tape wrap as seen in the photos.
