Electrical Starter blowing mega fuse to trunk battery

many do not want to remove solenoids from fords. I know there is one on the starter now but they are kept for several reasons. Auto ele is a lill beyond me. I wrked on that in the 60s & '70s so am not up to date (have -0- theory) The GMers uses the starter solenoid for most "add ons" (amps, fog lghts, etc, etc) so they find wires 'down in the soup' gettin caroded, etc - hard to reach, wrk on, etc. BUT there are system needs for the separate solenoid too (again, I don't have the theory so am not the best for explanation). The '3G' has some advantages over (gm) '1 wire' too. Again they can explain better (like a idiot light to tell U when the alt is weakening, B4 total collapse, to get U to diagnose/repair B4 it's too late).

thanks Mike. That's helpful~
I need to put in that relay. I have 5 grounds (I think) Bat to motor, motor to frame, motor to fire wall, dash to fire wall, ummmm...

"...you added additional grounding beyond what the factory..."
oh, yes, certainly did (as it's a '70). But not beyond the '94 - Y2K+
3G style. My problem is I removed the solinoid too (not recommended
by modders in the know) and have to bring in back some where/how. Being
a hack (with auto ele anyway) I just made "what works" w/o any theory, under-
standing or knowledge. Now I'm Eeyore (or maybe Kirmit: "Its not easy bein me.")

Just re-read the OP #1 post. I'm steeping on his thread. Let me run adifferent one.

"...I could add a solenoid to the trunk...
Put it up front, under the hood, close to the other runs (hide on back of driver's inner fender if wanting?).
Here's the alt wring

chrlsful said:

"...you added additional grounding beyond what the factory..."
oh, yes, certainly did (as it's a '70). But not beyond the '94 - Y2K+
3G style. My problem is I removed the solinoid too (not recommended
by modders in the know) and have to bring in back some where/how. Being
a hack (with auto ele anyway) I just made "what works" w/o any theory, under-
standing or knowledge. Now I'm Eeyore (or maybe Kirmit: "Its not easy bein me.")

Just re-read the OP #1 post. I'm steeping on his thread. Let me run adifferent one.

"...I could add a solenoid to the trunk...
Put it up front, under the hood, close to the other runs (hide on back of driver's inner fender if wanting?).
Here's the alt wring

Click to expand...

Under no circumstances connect the two 10 gauge black/orange wires to the 3G alternator. If the fuse blows in the 4 gauge wire, the two 10 gauge wires will be overloaded to the point of catching fire and burning up the wiring harness.

The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

I am very careful to maintain backwards compatibility, so I did things a little different. The white/black stator wire gets the insulation stripped back about 1 1/2" in the middle of the wire & cut in the middle of the stripped area. Then a short length of white wire with a 1/4" slip on female spade connector gets spliced on to the white/black wire. Slide on enough 1/4" heat shrink tubing on the white wire to cover the solder splice you are going to make. Next all 3 wires get soldered together & the heat shrink tubing gets shrunk. When you finish, the white/black wire looks like a "Y" with 1 white arm and 1 white/black arm. I left the black/orange wires connected to the original plug and did not do anything to them. When you are done, the original plug still has all the wires connected to it and they are still functional. The extra white pigtail wire that you spliced, soldered in & covered with heat shrink tubing is just long enough to plug into the 3G without much left over.

I ran the 4 gauge wire under the front of the engine next to the 4 gauge wire for the starter power feed.
It came up the same path as the fuel injector supply lines, and gets bolted to the power output lug of the 3G alternator. The 125 amp fuse is mounted on a plastic panel bolted to the stock ignition coil mounts. One of side of the fuse has a 4 gauge wire connected to the battery side of the starter solenoid & the other to the 4 gauge power feed wire for the alternator.

I had some 1" silicone aircraft heat shield tubing that I fed the 4 gauge alternator power feed wire through and tie wrapped & clamped it in place with some aircraft cushion clamps. That provided the wire extra protection from road debris and rocks. Some heater hose could be used to do the same thing.

I have an additional 4 gauge ground running from the power steering pump mount to the common chassis ground being pointed to in the photo.

Apart from the grinding I did on the mount bracket, there wasn't much to it. Rather than just grind a notch, I ground the whole web back to the thick part of the bracket. It looks much more factory that way.

Here is the reasoning behind using only a single 4 gauge fused power feed to the alternator. If you use the two 10 gauge black/orange wires in addition to the 4 gauge wire, you have two fused power feed paths. The total current capacity of the wiring is the sum of the fused paths. The 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 185 amps, which exceeds the capacity of the alternator. Overload can occur without the fuses blowing, damaging the alternator.

The worst case scenario is that the alternator develops an internal short to ground resulting in a catastrophic failure. The initial short circuit surge current is limited by the resistance of the wiring. The current in a parallel circuit divides up according to the resistance of the branches. If the 4 gauge fuse opens up first, the two 10 gauge black/orange wires will be carrying the short circuit surge current. Depending on the time lag of the fuse links, they may open up before a fire starts or they may not.


Alternator wiring.





If you have a 3G alternator, the white/ yellow wire is critical to proper operation. It is the voltage sense and regulator power lead that picks up the difference in voltage at the alternator output stud and the connection point at the starter solenoid. If you cheat and run it directly to the alternator output, it sees the voltage at the alternator output stud. It does not see the voltage at the starter solenoid connection point where it feeds power to everything else. You may have a voltage drop in the wiring between the alternator output stud and the connection to the starter solenoid. Thus you may have low voltage or less than the standard regulated voltage at the starter solenoid connection point. This makes for low voltage throughout the rest of the car: everything operates at less than full efficiency.

Starter solenoid wiring 86-91 model cars.

Connect the fused 4 gauge wire to the alternator and the battery side of the starter solenoid.


Starter solenoid wiring 92-93 model cars.


I would use a maximum of 125 amp fuse for the output wire that connects to the starter solenoid. High current fuses will carry 110% load for an extended time without blowing open.

no top of which...I have the pmgr/mini starter (all adapting '70 wiring).
I should just close the door as I leave...
Thanks for the above.

chrlsful said:

thanks Mike. That's helpful~
I need to put in that relay. I have 5 grounds (I think) Bat to motor, motor to frame, motor to fire wall, dash to fire wall, ummmm...

Click to expand...

Don’t get rid of any of those. Weird stuff will happen as power searches for a different path to ground.
Your headlights should also have a ground to leave alone unless it needs cleaned.

'...rid of those..."
they're all new that I put in. OE only had 2 or 3 (asa 60 amp system - battery to block, engine to firewall to dash, those 2 w/same bolt 1 frnt / 1 back of 'wall'...

"...head lights..."
yeah, 1 for all that. I swapped in H4s w/1 relay each, new heavier wire. Wasa kit.

"...needs cleaning..."
a '70 (52 yrs ol) has rusted grounds. I cleaned down to bare metal, shined it up, used bolts (1/4 20) or sheetmetal screws, then painted the connection.

Back to the OP's post. Check the cable connections and the cables themselves for corrosion.

My 93 Coupe started having hot start issues (dragging/slow rotation) and it has a full 4 ga wire setup with a 3G and battery in the engine bay. What I found after pulling every cable was that the 4 ga ground from the battery to the block that the copper was green and had corrosion. It was in excess of 10 years old so I replaced it and the problem went away. Fast forward a couple years after that (last fall) and next up was replacing the mini starter. Checked out fine but the car would not hot start. Finally got fed up and just bought a reman unit with a lifetime warranty and problem solved. I ended up wrapping the new starter and the wires going up to the inner fender mounted starter solenoid with header wrap (stainless steel ties) to help with head soak. The exhaust system is full length shorties with a 2-1/2" X-pipe so its not super tight but I figured since I was in there might at well try the wrap. The failed starter was a salvage yard unit that I used to convert the car to a mini starter 15+ years ago and it had been rebuilt a couple of times. My guess is that it was just mechanically worn out and coupled with some heat soak it couldn't do it any more.

The T-Bird has a trunk mounted battery with 1/0 welding cable with a 11:1 351W, mini starter, and a 3G alternator. The rest of the wiring with regards to the battery, starter, and alternator is 4 ga. I have never had a hot start issue with this car and have a 250A fuse on the 1/0 cable from the trunk to the inner fender mounted starter solenoid. Ran 4 ga from the other side of the starter solenoid to the mini starter and a 4 ga wire with a 150A fuse from the 3G alternator to the battery side of the inner fender mounted starter solenoid. The 1/0 is capable of carrying in excess of 250A at the length from the trunk to the front of the car (less than 20 feet). This car has custom full length headers with 1-7/8" primary and 3-1/2" collectors so its a little tight. Starter and cables are wrapped with header wrap like I did on the Coupe.

If you are popping a 175A fuse on a hot start I would say you have other problems and the fuse is just doing its job. Granted I am assuming you have all oxygen free copper (OFC) fine stranded wire in the car and not aluminum or copper clad aluminum (CCA) fine stranded wire. Just so you know CCA carries about 60%-70% of the ampacity of the same diameter OFC wire. Basically just stay away from CCA as it also heats up more, looses voltage faster, and corrodes faster per foot than OFC.

sounds like U kept the 2 solinoids too...

chrisful,
If you are referring to the starter solenoid on the starter and the one on the inner fender then yes he did and refer to the info in Post #3 by Mustang5L5's as to why you want to. As many mini starter swaps as I have seen this is by far the most common way it is done.

yup, I'm in trouble now'n gotta go back (it comes in the shop for winter/has time put it). Thnx 1 & all.

Two things. First is check and make sure your grounds are in good shape because if they are not it will cause the current to spike. I would check from the battery to "frame" and "frame" to engine block. You should voltage drop test the connections and cables. Second, pull the starter and have it checked as they ground to their own case which when bolted to the bell housing is how they get their ground.

Typically the wire from the battery to the mini starter or starter solenoid to the larger starter do not have a fuse on them. This is due to inrush current when starting the car will be momentarily high then settle down.

With all this said I would check the ground connections, the ground cables themselves, test the starter, and then if all of that is good then move up to a 250A fuse and see what happens. The 1/0 cable can support right at 300A at a distance of 20' so the 250A fuse will still protect everything.