jimculp

I'm (well my mechanic is) placing the Autronic ECU under the drivers seat. The wiring harness does not seem to provide enough slack for the wiring to reach the engine compartment with room to spare. The Autronic rep is making a detatchable wire section for the motor area which will be able to be plugged and unplugged into the wire section coming from the ECU. Is this common?

It would seem that if the motor ever needed to be pulled that the detatchable method would be much better, but I will be adding additional complexity to the system which I'm not wild about. How is this usually done?

TIA

Geoffrey

I almost always install a milspec bulkhead connector on the firewall for the ECU and associated wiring and is common practice. This allows the engine to be dropped by disconnecting only one electrical connection. Fortunately for you, the Autronic wiring harness does not use good quality wire and shielded reference and sync cables to supress noise which would add complexity to using an intermediate connector due to the special connectors required for the shield. The other issue you'll have is maintaining consistent wire color.

jimculp

I suppose you mean unfortunately for me right? Thanks for the info.

Edit- OK, so what you're saying is that although the Autronic wiring does not offer shielded reference and sync cables, it does'nt matter because the section that's exposed to the engine compartment will (or should) be so it does'nt matter that the Autronic wiring is'nt the best right?

Rob S

Jim,

I think there are two sides to this coin.

In your case it may make good sense to make a two-piece harness, because you came up short on length. But I believe that the two-piece harness is not necessarily preferable. It depends on how you're going to use your car. If you're racing and are likely to drop the engine frequently, and in a hurry, and -- importantly -- you're not going to be removing the harness from the engine anyway during the drop, then a two piece harness may make sense. But if you only take the engine out occasionally, the speed of undoing one big connector (instead of about 13 small ones) may not make it worth the bother and cost -- and risk -- of that connection. Electrical systems usually fail at the connections; a bulkhead connector introduces three additional connections per conductor (two wire terminations plus the pin/socket interface). A one-piece harness eliminates this concern. I've found that to undo the 13 terminations at each sensor on the engine takes a trivial amount of time (maybe two minutes at most), so to have a two piece harness doesn't buy me much. And if you don't have shielded wire, then to group all those wires in close proximity, such as at a single bulkhead connector, may increase the risk of electrical interference in the harness. Cost may be a factor too. Those bulkhead connectors can be really expensive -- easily $100 to $200 just for the connector.

Another alternative to lengthening the harness may be to somehow locate your ECU closer to the engine on the interior side of the rear bulkhead. You might have to get creative with ways to hide it or disguise it a bit, though.

jimculp

Thanks Rob- great information.

DonE

I agree with Rob.

I used a 22 pin weatherpack connector, but found out that the connections were not sufficient for good connectivity. Once I removed it, my sensors were more stable. I am installing a new ECU and I will not be using a bulkhead connector - the harness will reach from the ECU to the sensors in tact. If it takes me a couple more minutes, so be it for a piece of mind.

125shifter

I'm planning to use a milspec bulkhead connector for my ECU, but this has me concerned. What about having a hole in the bulkhead large enough to pull the ECU harness and plug through the hole?

Geoffrey

While what Rob says is true, that connections are not as reliable as a "home run", I have never, ever had any issue with either a Milspec, or Autosport connection on any track or street car I've worked on. Thse $100-$200 connectors are far better in quality than the $2 weatherpack GM style connector Don was using. If you look at a DP or ALMS car, you will find the autosport and milspec connectors used everywhere so sub harnesses can be replaced quickly and easily. Further, if you look at factory Porsches, they use two large round connectors to attache the engine wire harness to the chassis wire harness, and I can tell you that they are not the quailty of a milspec or autosport connector.

Here is a picture of one of the harnesses in my car.

jimculp

Geoffrey,

Could you describe your ignition setup and reason for their mounting locations?

Thanks,

Jim

Geoffrey

My engine is an 8000+ rpm engine and the factory ignition system cannot provide full energy after 6666rpm based on the coil dwell time. I am running a MoTeC CDI ignition system and the factory twin distributor. This allows me to run a plug gap of .080" in N/A form or .060" in turbocharged form. Electronics should not be hard mounted directly to the chassis because the vibration will eventually crack the traces on the PC board. Race cars with solid mounts are even worse. The CDI units are mounted using stand offs and are on the rear firewall due to a lack of a better place.

jimculp

Geoffrey,

What is your take on locating the CDI boxes in the engine compartment? I'm considering the engine location and thinking of locating my CDI boxes in passenger side "footwell" for the back seat and my ECU in the other footwell. I'll run the wiring beneath the carpeting and between the seatbacks to two gromets in the firewall (one opening for the CDI's wiring and one for the ECU). I'm trying to keep the boxes out of sight since this will be a 80% street car.

Any suggestions?

Jim

125shifter

That makes me feel better about the connector. Geoffrey, does the Motec unterminated harness have enough wire to do the whole harness with the bulkhead connector?

Geoffrey

The MoTeC unterminated harness has 10' of length. In general, you need more that 10' to place the ECU under one of the front seats. As with most things MoTeC, they can probably make a longer unterminated harness.

You would need to check with your CDI manufacturer to determine if it can be exposed to the elements. In general, I try to avoid electronics in the engine bay where it is hot, oily, and exposed to rain and dirt. CDI units also have recommendations as to length for the primary current wires and runs to the distributor. It is good to keep CDI wires to the coil seperate from ECU sensor wires. The passenger foot wells are probably as good a place as any for the ECU and CDI units. I'd take power and ground for the CDI from the starter.

ngoldrich

I too have milspec bulkhead connector on the firewall. I have used that on most of my cars with very good luck.

Norm

DonE

Geoffrey

Good info on the connectors. You know I did my entire wiring and used the proper equipment, but still had a few connection problems (just a couple besides the weatherpack connector). You are talking about milspec stuff and additional crimpers, and some experience in making these types of harnesses and connections. Unless I am planning on pulling an engine on a regular basis, would you still recommend the +$100 connectors and the proper crimpers (+$100 each) for most of us?

I will be locating my ECU in the rear foot well again, with stand-off's, then routing the harness through the bulkhead, over the torque tube, then between the body and cross-body support where the shocks are mounted. This seems to be a clean installation when using the shrink tube, and is easy to remove the sensor plugs. On a street car, where do you come in through the bulkhead?