Here is the scoop on the #4 relay. I had the information in my notes. If your car is one of the later USA emission versions that has the decelleration solenoid (lower one of two on the injection pump), then it was equipped with this fourth relay, along with the large RPM relay over by the coil. The car should also have a micro switch mounted on the firewall. There is a separate wiring harness which is added to the car to run all these devices. This add-on wiring harness is a bit complex but one end ties into the neutral safety switch on the firewall and meanders to that fourth relay which is a five prong relay instead of a four prong (as is the other three). After leaving the neutral safety switch on the firewall two wires (green/black) and (green/white) branch-off and connect to the micro switch on the firewall. Next a wire from inside the car is feed into this harness (I suspect that this is the wire coming from the fuse box). Next along the way a brown ground wire emerges and is attached to the ground lug on the relay brackets with the some other grounds. Next a four-wire bundle branches-off and plugs into the large deceleration relay (near the coil). The four wires here are brown, black, black/red, green/blk. Next down the harness a green/black single wire branches off and connects to the ignition coil. Another single wire branches off next and connects to the fuel shut-off solenoid on the injection pump. Lastly a six terminal plug attaches to the bottom of that #4 fourth relay. The fourth relay is a five prong relay as mentioned and two sockets of the six prong plug are empty. Other wire colors in this plug are black/red, green, green/red, and black. So that's as much as I know on the #4 relay. Hope this helps. I suspect that the short circuit in your system might be the lower solenoid on the injection pump. You may consider simply just disconnecting it as is done without consequence on many cars.
