Here's the relay from my '88.




The fat red wire comes from the battery and connects to the big post. The other wires on the post provide 12v to other circuits. If you follow any of those wires, you'll find a black "barrel" a few inches from the connector. Those are the fusible links. You can see the one on the fuel pump ballast resistor.

So the one on the lower right is the ground. On an auto trans, this grounds through the NSS when in park or neutral.

The one on the lower left, comes from the ignition switch.. When you turn the key to START, it applies 12 v to the relay and (if the trans is in P or N), energizes the relay and sends 12v down the larger green wire just above it. This goes to the starter solenoid.

 

I have one of those cheap ones with the lights. I never really have done any electrical checking before. Stubborn. I know it is not difficult, just stubborn. But now I am doing this stuff, I am willing to try. I can send a pic later of what I have. If I need to get something decent, I can. Actually I might have something, but I have to check. Thank you.

 

That would be a fusible link. Basically an undersized piece of wire that is meant to melt if too much current goes through it.

 

Now I am understanding. I thought that piece was repaired at one time.
So do I just repair it with regular wire or do I use something to recreate the safety feature like an actual fuse or is there such a thing as a repair (fusible)?
Do you think it was the constant off/on I did when repairing my window tracks and greasing my window motors drew too much and burned that out? Also I remember too that I was turning on and off for a socket for the front turn signal but I believe I had it started at that time.
By the way I just ordered a digital multi meter. Start playing with it and learn something.

Thanks

 

If you Google search fusible link you'll find plenty of options. One of which is a wire with an automotive fuse in it. If your all un-molested stock and prefer it that way, we'll have to figure out which one is the right one for that application. I need to pause from offering up more advice on this until I understand the system a little better. I'm sure one or more of the Vets can help with that. I believe there is power going to the fuel pump at all times through the ballast resistor while the key is in the run position. I believe it gets the 2 second (ish) priming burst through the fuel pump relay with the timing signal coming from the ECU. And if that is the case, I don't understand what allows the fuel pump to pause after the priming burst until the engine is running, because that is what actually happens. My '88 fuel pump primes when I roll the key to run, then goes quiet. The fuel pump then runs continually while the engine is running. My '66 Mustang works in a similar fashion with the ignition coil. Power comes from two directions: 9v through the ballast resistor while in run and 12v from the starter solenoid while cranking. In the case of the Mustang, the power actually comes from two sources while cranking and the 12v source is dominant. With the RENIX fuel pump that doesn't seem to be the case. Power seems to be either from the fuel pump relay OR the ballast resistor power connection on the starter relay. What I need help understanding is what/how is the signal that allows/controls the flow of power to the ballast resistor? I think you stand a good chance of burning another wire in two without understanding this.

 

"Fuel Pump Controls—4.0L Engines
The fuel pump circuit of MPI systems are equipped with a ballast resistor to reduce fuel pump noise. Voltage to operate the fuel pump is supplied through the Fuel Pump Relay except during engine starting (cranking) and wide open throttle conditions. Ground for the fuel pump relay is controlled by the engine Electronic Control Unit (ECU). During engine starting the fuel pump relay and ballast resistor are by-passed and voltage is supplied to the fuel pump through the starter relay. During wide open throttle conditions the fuel pump relay and ballast resistor are again by-passed and voltage is supplied to the fuel pump through the oxygen sensor relay."

The color of the wire on the fusible link denotes the gauge (instead of amps). You can barely make out 18ga on the green wires. The browns are 14ga.

 

Very helpful. Then to read back what I think that says, the ECU sends/removes the signal to the starter relay ground terminal to control whether or not power is being supplied from the fuel pump ballast resistor terminal on the starter relay. And if I have understood that correctly, then it is the ECM that pauses the fuel pump after priming until it also receives CPS signal that the engine is running.

 

I should probably apologize for hijacking this thread with such a tedious sidebar. However, I do not think that the assumption made that leaving the key in the "Run" position for an extended period of time would burn out the fuel pump is valid. There should be no power to the fuel pump after the initial prime through the fuel pump relay when the key was first turned to "Run" - until the engine is running, which it wasn't. Neither would leaving the key in the "Run" position burn the power supply wire to the fuel pump ballast resistor in two, for the same reason. It is possible that when changing out ballast resistor(s) in post #18 that the supply side was shorted to ground causing the fusible link to burn, but I really think it prudent to verify there is no continuity to ground (short) through both the ballast resistor power wire and again at the powered side of the fuel pump relay socket before reenergizing with 12v.

 

So at this point I don't know how to check that.
I am also sending some pictures of the fuse land trying to find a replacement for it. I am not finding any luck in finding a replacement for it. I sent some pictures of what. The red or orange and black wire looks like and also the reddish looking fuse link. the fuse link appears to say 20 gauge and I'm sending. Of what appears to be 20 gauge.

 

Belden 20 ga. Fusible Link Primary Wire BEL 785810 | Buy Online - NAPA Auto Parts (napaonline.com)

When you receive the multimeter, just let the forum know and someone will definitely step up to help you do some resistance checks.

 

Thank you. Should be in tomorrow.

 

Hmm. it certainly says 20ga. Here's the chart from the FSM. Say 20ga=Orange. I'll go back out and check mine. Perhaps 35 years ago, they were orange.

 

So I am going over to the only parts store locally that I can find a 20 gauge fusible link wire and I think it is gray or green or something not red/orange. Is this correct? And yes it is Nappa, I just checked the link that was sent. But I will check back when I get the multi meter so I can check everything before I attach a new fuse wire. Thanks

 

As long as the gauge is correct, the color shouldn't matter. These were the colors Jeep used back in the day.

 

Good morning from CA, I did get the multi meter. I have not done anything like this. At 53 I just started this hobby rebuild stuff and learning. I mostly all my life patched farm equipment but never really mechanic. I have the fuse still to repair, the battery out and that extra ground on the pump side of the harness.
Also this weekend I hope to pull the dash, cluster out to check that fuel gauge. I did get a new fuel pump (premature) but the one in there is new as of last year and no more than a few hours or less than a mile on it.

So I am completely clueless unless I start watching some YouTube...lol. I appreciate the help.
Thanks