[Cody]

Both yellow wires are in fact getting 12V. On the relays it is true the #5 position would be the closed position until power is applied to the coil of the relay and then the switch would make contact with the #4 position. The original like I said only had 4 pins but operated to the same logic for both the EEC and FP relay. It shouldn’t make a difference then between a four or five prong relay as it can only be connected one way anyway.

[Cody]

Correct, the yellow wires are hot all the time as the Haynes manual shows. The manual has a list of what the voltage ranges should be on each wire of the relay and I believe it showed 4 to 6 for the red wire. I agree though it should be a full 12 volts to properly open the relay and supply sufficient power. It appears that it is constantly leaving the FP relay open with the key on because it is trying to prime the fuel rail but can’t due to lack of power to the fuel pump.

[Cody]

Sorry for the confusion let me clarify. Both relays have 12 volts on the yellow wires, the fusible links on the diagram. With the key on the EEC relay receives 12 volts to open the relay but the red wire where voltage travels once the relay is open only puts out 2.7 volts or so. I’m my opinion that is nowhere enough to open the FP relay to which the red wire runs. The voltage on the brown wire is even lower than that of the red wire. The brown wire is the hot side of the inertia switch and from there it feeds the fuel pumps. Keep in mind the voltage can be checked on the brown wire of the inertia switch and it has low voltage similar to checking the brown wire directly at relay. I’m assuming due to the low voltage feeding the wires and resistance in the wires some voltage is lost by the time the wire reaches the fuel pump as it only reads 0.01 volts which is basically 0. I’m beginning to wonder if the relays are correct. The original relays are four prong so I had to special order the aftermarket relays. The relays they stock for the truck are five prong and that has been bothering me since the original is four prong.

[Cody]

I checked the inertia switch and it’s not tripped and has continuity. The voltage is so low coming from the relay that the voltage at the inertia switch is very low.

[Cody]

The fuel pump is not humming when turned the key is turned on and there is no power to its electrical connector. It has good spark and good power going to the relays just no power to the fuel system.

[Cody]

That is correct the red wire only reads low voltage (2.7 V) when checked with a multimeter and isn’t enough power to make a test light come on when tested that way. The Haynes manual says that the red wire should have 4 to 6 V but I have read online that it should have 10 to 12 V.

[Author]

Replies