Positive Cable Routing from Trunk

[Alan_C]

Although not for a Factory Five, I have a question regarding the positive cable routing in my 70 Mach 1 restomod. I am using a 2nd Gen Coyote and the battery is located in the trunk behind the PS rear tire.

My plan is to run a 0/1 AWG positive cable from the fuse block at the battery directly to the starter. This run will exit the trunk area and run under the floor of the car. I have subframe connectors and the cable will be secured to the PS SFC. I will run a 2 AWG cable from the alternator to the starter, although I could run the same 0/1 AWG. I plan a run of 4 AWG cable from the fuse block at the battery to the Power Distribution Block mounted to the interior side of the PS firewall. This cable will be run in the normal wire trough from the trunk area to the passenger footwell. The path from the battery to the starter is the high current path, therefore the largest cable. I wanted the minimum voltage drop from the battery to the starter. The path to the power distribution block does not feed any high current accessories as I am adding external relays for the dual cooling fans.

On my MK4 with the battery in the rear of the car, I felt the 4 AWG wire was marginal. With the concern Ford has shown over having the battery too far away from the PCM, I figure that increasing the cable size to 0/1 AWG for the run to the starter will make the battery appear "closer" as it will provide less voltage drop due to cable resistance.

There is far more experience with Coyote installs here than on the Vintage Mustang Forum. Comments on my plan would be appreciated.

[AC Bill]

I misread your post initially, and had to rethink my reply.
#1 would not be a good choice from a trunk mounted battery, to the starter. #4 would be a better choice, as it has offer far less resistance. It can handle 300 amps over that distance. Your starter could draw as much as 250 amps when cranking.

[Old Timer]

It's easy to get power cable sises mixed up. You start getting bigger as size numbers go down, until you get to 0 gauge, then you get bigger as you add 0s like 00 or 000, and we won't get into mcm sizes.

To run from the back of the car to the front, the 0 or 1AWG wire should do fine.
The 4 gauge will work if it's short to feed the starter, if more then a foot, I would go up to 2 AWG to minimize voltage loss.

If you need flexible cable, you can pick up welding cable and use it. It is more costly!

[Jeff Kleiner]

I misread your post initially, and had to rethink my reply.
#1 would not be a good choice from a trunk mounted battery, to the starter. #4 would be a better choice, as it has offer far less resistance. It can handle 300 amps over that distance. Your starter could draw as much as 250 amps when cranking.

You have it backasswards Bill; #1 is much larger than #4 and would be preferred for a long run. Many of us have found that #4 cables are insufficient or at best marginal for a trunk mounted battery in our roadsters.

Jeff

[RoadRacer]

LOL, this is so typical - I just (like last weekend) made a new battery cable for my 33 (slightly longer for better routing to trunk) out of some #4 I had lying on the shelf. :(

[weendoggy]

LOL, this is so typical - I just (like last weekend) made a new battery cable for my 33 (slightly longer for better routing to trunk) out of some #4 I had lying on the shelf. :(

I doubt you'll have issues. I have my MKI with IRS and battery behind pumpkin and run a #4 to my cutoff switch behind the seat and then to the starter. No issues in over 21yrs.

[Alan_C]

When I built my MK4 in 2011, I used the #4 AWG cable supplied with the kit. I worked well most of the time, but when the battery was not freshly charged, starting was sometimes difficult. I had a 4.6L DOHC, the predecessor to the Coyote, in my Cobra. I recall Ford Performance had noted in their instructions not to have more than 10 ft. between the battery and the PCM. In the Cobra, not an issue with the short wheelbase. In my Mustang, I have the PCM mounted in the front corner of the PS wheel well and the battery behind the PS rear wheel well, which exceeds 10 ft. To keep voltage drop to a minimum during starting is the reasoning behind using the heavier 0/1 AWG cable between the battery and starter. Once started, I believe a 4 AWG will supply sufficient voltage to the PCM as the alternator charges at more like 13V. This is why I had the parallel path, heavier direct to the starter and a bit smaller to the power distribution box.

[AC Bill]

You have it backasswards Bill; #1 is much larger than #4 and would be preferred for a long run. Many of us have found that #4 cables are insufficient or at best marginal for a trunk mounted battery in our roadsters. Jeff

Well that was embarrassing..lol. Yes I did have it assbackwards..:o

Alan , just switch the numbers in my post, and you should be good to go..:)