3.6 conversion wiring harness question, fuse at the battery

[chuffysplace]

The car i have (new to me), has a 3.6 conversion by Instant G. It has a (it looks manually made) wiring harness that goes from the drivers seat area to the front trunk. It plugs into the fuel injection harness under the seat and then runs to the following items:

1) Fuel Pump
2) Battery
3) Tach
4) Switched Ignition (12 volts when the key is on or cranking)

The issue I had today was that the connection to the battery, which had an inline usable link, shorted out. The car immediately died. At first I thought maybe it was arcing but now I am wondering, if there is enough 'fuse' there. The fix to replace it was pretty easy, at the time, I didn't know, so I replaced it with another similar fuse-able link. but I have to wonder what kind of draw this connection needs. I am carefully keeping an eye on the new fuse able link, and I notice it gets 'warm'. Although I am not sure what it is rated for, it has 12 gauge wire and I put a 20 amp fuse in in. The fuse doesn't blow, but the link itself does gets a bit warm after driving around a while.

Does this sound right? Do I need a larger fusible link, maybe a circuit breaker, relay or similar, or dare I say...do I have an incorrect draw issue maybe?

[chuffysplace]

[ischmitz]

The original 964/993 implementation uses a 4.00mm wire un-fused from the battery straight to the DME relay. The wire runs to the 6-pin connector under the seat. From there it powers the injectors, ignition coils, fuel pump, and all other actuators on the engine through the DME relay's 2nd stage. 20 Amps seems marginal and a 12-gauge (~2mm) wire is plain too small. Scary.

FWIW I have seen bicycle hardware used for the throttle linkage on those conversion kits, not cool....

Ingo

[chuffysplace]

Thanks for the info. Wow, scary. I wonder if the 4.0 mm is needed for this application. It probably is. That would be like a 6 or 7 gauge wire. I will have to check Patrick Motorsports conversion kit, see how theirs is setup.

[Tremelune]

20A is fine for a 12awg wire, but it is the maximum. If you need to draw more power, you'll need larger wire. The first thing you'll need to know is the total draw of all those components. Fuse at the battery, whatever you wind up using.

I have never, ever seen a fuse fail that catastrophically. Really looks like a short to me.

[pors1968]

The fuse holder look like realy poor quality the fuse should blow before it melted.

[chuffysplace]

Hey guys thanks. I do have to verify the current draw. Yes, I think the issue is with the fuse holder; poor quality, maybe defective, etc. A suggestion was made to me to just use an unused fuse in the stock fuse box. I like this idea, much cleaner and safer too. Thanks again.

[Joe Bob]

Timmins has used some Mickey Mouse stuff. Ingo has seen some of the MM stuff on my 3.6 conversion.....yes I have a bicycle brake cable on my throttle linkage.

At least he is better than Patrick Motor Dorks.

Have you tried calling Timmins?

[ischmitz]

Originally Posted by chuffysplace

Thanks for the info. Wow, scary. I wonder if the 4.0 mm is needed for this application. It probably is. That would be like a 6 or 7 gauge wire. I will have to check Patrick Motorsports conversion kit, see how theirs is setup.

ask yourself why Porsche used 4.00mm and you have your answer....

While you can probably get away with smaller diameter wire why go marginal and risk melting insulation and poor performance. The thick wire ensures minimum drops (voltages sags). Remember, some of the loads are not constant but put sharp transients onto the battery (e.g. coil charge, injector opening).

Ingo

[chuffysplace]

All good points and suggestions. Thanks again.