Re-wiring tips for Motronic cars

[Jazzbass]

Need to go in and hack up your wiring harness to install a 3.6 in an older car? Mice at your old harness? Here are some tips from the thread where I went insane and rewired a 944 (http://dorkiphus.net/porsche/showthread.php?t=12662)

[Jazzbass]

I've gotten several PMs and in person requests for some more info about this project. So I thought I'd post another follow up with info for those who are as dumb as I am and attempt this on their own.

Parts

AMP Junior Timer - This is the official name of the connectors that are so ubiquitous in the Motronic wiring. The only source I've found for them domestically is Eagle Day (http://eagleday.stores.yahoo.net/ampconnectors.html). Not surprisingly, they're expensive as hell.

11896

Molex Mini-fit Jr - these are great connectors for internal connections where you don't need a weather sealed connection. Mini-fit Jr are one of the most popular connectors in the industry, so they're cheap, available in tons of different sizes and configurations, and easy to get from Mouser or Digikey. I used 20 pin mini-fit jr. connectors when wiring in the dash panel of TD's fo-fo.

11895

Weather Pack - Most of the connectors I used in the project were Weather Pack connectors from Delco/Packard/GM. I picked these because they are a high quality connector that is weather sealed and readily available. To start the project, I bought a starter kit off eBay for about $200, which was a pretty good deal. Weather Pack stuff is also available at my local Pep Boys in case I run out of something. The Pep Boys option is a last resort mind you. I estimate that each connection, when materials are bought in bulk, costs about $3.50. That's the cost of the male and female connectors, all the pins and weather seals. At Pep Boys this cost is more like $10 per connection.

Weather Pack, like most of the connectors I use, are "open barrel" connectors that require a special crimping tool to use. Once crimped, though, the quality of the crimp is vastly superior to the closed barrel type crimps you can buy at you FLAPS/Home Depot (the red/blue/yellow). Also, you have to make sure you match the connector pins to the wire gauge. They make Weather Pack pins for 18/20ga, 16/14ga, and 12ga. Maximum power through the connector is 20A.

80538054

Metri Pack 280 - same basic idea as the Weather Pack. Open barrel connectors, weather sealed, made by Delco/Packard. Metri Pack are more expensive than Weather Pack, but can handle up 30A. Basically, I only use these in high current situations. I got these from Del City.

They also make Metri Pack 480 (42A), 630 (48A), and 800 (60A) connectors, but they are more difficult to find. I didn't use any of these.

8055

Closed Barrel Connectors - well, I say a lot I don't like these, and I don't really. But they're easy to find, esp for spade connectors and full eye connectors. However, I use them a little differently than most. I pull the red/blue/yellow plastic part off and use an open barrel crimper to crimp the connection. The result is a much better crimp than the std closed barrel crimp through the insulation. Because I take the insulator off, I use heat shrink to replace it. I like this better, btw, because it allows me to extend the insulation to cover part of the wire, too, which provides a bit of strain relief.

Switches/Relays/Lights - Standard 12V stuff bought at the FLAPS, Radio Shack or Del City. Just make sure the amperage ratings are right for what you're doing.

Wire - I tried to reuse a lot of the harness I cut out of the car. That would give me factory wire, in the right gauge and color. When that wasn't sufficient, I supplemented with wire bought from Advance, Pep Boys and Home Depot. All of them carry primary wire in std colors (red, yellow, blue, brown, black) and std US gauges (10, 12, 14, 16, 18 ).

Documentation

Factory Manuals - The wiring diagrams in the factory repair manuals are, IMO, absolutely critical for this job. There have been several links posted here and on other BBSs to sites where you can download these manuals. I'm not going to post them here for liability reasons, but they're out there. Get them and learn to read them.

The factory wiring diagrams tell you everything about the wiring in the car -where the wire starts, what color it is, what gauge it is, what connectors it goes through (and what pin on that connector it is). If you're rewireing a car, it's most likely because several people came before you and f**ked everything up. That was the case here. The factory manuals can help sort a lot of this stuff out.

Microsoft Visio - I actually used Visio as a poor man's schematic capture tool to draw the new wiring diagram for the car. In fact, I probably spent 15-20 hours designing the wiring in Visio before I ever made a connection. As an EE, this is the way I'm trained to do things. IMO is exactly what you have to do here. In a situation where there are over 100 circuits to run, it's no time to start "winging it". Leave that to the stereo installation guys. If you do the design right up front, when you go to wire things should go smoothly. The proof to all this is that when I was done wiring, the car started up on the first try.

I tried to mimic the factory diagrams as much as possible. I spec'd wire color, gauge, what connectors they went through and what pins on those connectors were used. The diagrams included all connectors. I gave each connector an ID, and used labels on the connectors to ID them. Sound anal? Hell yes it is. But in a job like this, it's the difference between making a 10 minute repair at the track (or the side of the road) or spending 3 hours trying to figure out WTF you did when you rewired 8 months ago.

Another benefit of doing the design first is that I could get help. Charlie came to help me with TD's car. I gave him a page of the diagram and said "have fun". It told him what wire and connectors to use and where, and he could wire his part of the car without needing my help.

Tools

Crimpers- You need good crimpers for this job. The Weather Pack and Metri Pack stuff above use std open barrel crimps for the wire connection, but need a special crimp for the weather seal. I bought two ratcheting crimpers for the Weather/Metri pack stuff - the T-13, a 20-14 gauge crimper and the T-17, a 12-10 gauge crimper:

8064 8063

These are good quality ratcheting crimpers and run about $100 each. The 20-14 ga ones suck. The 12-10 ga ones are awesome. The 18-14ga ones don't crimp the wire tight enough (look at the pick of the red handled crimpers - too much space in the crimp area when closed). I consider the 18-14ga crimpers a complete waste of money. They sell a new, cheaper non-ratcheting crimper for this stuff now called the T18:

8066

The crimp areas look a lot better, so this might be a good choice for those on a budget.

A good, inexpensive all purpose open barrel crimper is the Molex 63811-1000. About $50, but with a ton of crimp slots for pretty much every size connector.

8067

Finally, I just found a great deal on a cheap, ratcheting style crimper from Del City. Item #990168. $30 and it's a pretty nice unit. The only drawback (or benefit, depending on your perspective) is that it's made for std open barrel crimp connectors that crimp into the insulation of the wire, like this:

8068

It makes both the wire crimp and the insulation crimp at once. With the Weather/MetriPack stuff, you don't crimp into the insulation, you crimp that part of the connector around the weather seal. That said, you can insert the pin into these connector backwards and use it for everything except female Metripack pins. For the weather seal connector, you still need to use one of the special Weather/MetriPack crimpers shown above.

Pin extractors - For all types of open barrel crimp connectors, you crimp a pin to the wire, then insert the pin into a connector where it sanps into place. If you screw up and need to re-crimp or reposition the wire, you need a pin extractor to get the pin out of the connector. Here's what the MetriPack extractor looks like:

8065

These tools are cheap - about $4 each. They make them for Weather Pack connectors, too. Buy them, you will need them.

Other Tools - In some cases I soldered the wires into the pins. You have to be careful here, as I explain in the thread. Soldering makes the point where the wire goes into the solder brittle and will become a failure point over time. I know lots of people believe soldering the the best possible way to join a wire to something, but in a lot of cases that simply isn't true. Crimp connectors is one of those cases. Do a Google search, there have been several studies on this, one notably by VW.

So, if I did solder, I soldered only the top portion of the wire to the connector. I didn't allow the solder to wick into the wire very much and make the point where the wire left the connector stiff or brittle. To do this requires a soldering iron with the right heat range and some practice. If the iron is too hot, the wire will heat up too fast and will suck up too much solder. If you're going to solder for that extra level or protection (and, having done it once, I can honestly say I wouldn't do it again), get a good iron with a controlled temperature tip. I use a Weller TCP series iron - it was about $150. Not cheap, but a good soldering iron isn't. The ones you get for $10 at Home Depot? Crap. Don't use these.

I also used a LOT of heat shrink tubing. They have good stuff at Home Depot or Del City. I use a cheap, $40 heat gun to shrink it. The lighter method sucks because sometimes you can't get under the wire and half the time when you do, you end up burning the heat shrink. So get a nice $40 adjustable heat gun from Home Depot.

Suppliers

All in all, I probably spent $800 on parts for the rewire. Yeah - $800. This includes cost of the crimpers, wire, connectors, switches, aluminum plate, relays, etc. Everything (except the $200 worth of crimpers) it cheap - it's just that you end up buying a lot of it. Death by 1000 cuts so to speak.

Locally, I get a lot of stuff from Advance Auto, NAPA, Home Depot and Pep Boys. NAPA was esp good for brown wire - which is ground in these cars, BTW. Please don't use black. I know you 72 Chevelle used black as ground, but that'll just confuse the hell out of the next guy that works on the car.

I was able to get most of the switches, fuse blocks, wire, closed barrel connectors and heat shrink tubing from these places.

DelCity.net (http://delcity.net) - One of my favorite places to order from. Lots of selection, great prices and great service. If you order something that's out of stock, you typically get a phone call from a real person that same day. This is where I get all my MetriPack and WeatherPack stuff from, in addition to some specialty switches (E.g. 4PDT) and relays.

DigiKey (http://digikey.com)and Mouser (http://mouser.com)- good source for some smaller open barrel connector stuff like Molex and Amp connectors. Not weather sealed like the Weather Pack stuff, but good for interior work with smaller gauge wire and higher density connectors (largest WeatherPack connector is 6pin; you can get 24pin Molex connectors).

[Jazzbass]

Speakings of wire gauge, make sure you know what's going on with the wire gauge in terms of how much load is on the circuit. What gauge is right depends both on how much current the circuit will carry AND the length of the wire itself. For example, most people spec 12ga wire for a 20A circuit. However, I can use 18ga to carry 20A for 4in if I want (say in a fuse panel).

The key here is that wire has resistance. As you increase the length of the wire, you increase the resistance. As you increase the diameter of the wire, you decrease the resistance. Thus, for a fixed current (say 20A), the longer the wire, the bigger in diameter it needs to be. Why? Heat. The problem is that as the resistance of the goes up, more current generates more heat. In fact, the amount of heat generated in wire goes up exponentially as the current goes up. In geeky EE terms, the equation is:

P = I²R

where P = power (heat), I = current and R = resistance. Thus, if you double the amount of current through the same piece of wire, the heat generated goes up by a factor of 4.

I used this chart to decide what wire gauge to use for the various circuits:

8069

AWG - Metric Conversion

All the wire you buy in the US is spec'd in AWG - 20ga, 18ga, etc. All the wire in your German car is metric. Porsche spec's all of their wire gauges in the diagrams in mm². I use the follow conversions when rewiring:

4.0mm² = 10ga/12ga (Actual 11ga)
2.5mm² = 12ga/14ga (Actual 13ga)
1.5mm² = 16ga
1.0mm² = 16ga/18ga (Actual 17ga)
0.5mm² = 20ga

As you can see, most of the common gauges Porsche uses don't match up to a AWG size you can readily buy. In these cases you have to use your judgment about what gauge wire to use. How long is the run? If it's short, you can probably get away with the smaller gauge (14ga for a 2.5mm² wire, for example). If it's a longer run, go up a size (12ga for the 2.5mm²).

[rs911t]

Day-um! What a day for geek posts! :lol: How about wiring a 3.2 in an older car? ;)

[Jazzbass]

Day-um! What a day for geek posts! :lol: How about wiring a 3.2 in an older car? ;)
As long as you have the whole DME harness, it's actually a piece of cake. All of the Motronic signal wires are in the DME harness, so it's just a matter of supplying power where needed. And with a 911 Carrera, the DME relay is part of the harness itself, so you don't have to wire it in separate like I did with the 944. I can get you a copy of the DME wiring if you need it.

[Jazzbass]

Updated the above post with more info on Junior timer and Mini Fit connectors.

[rs911t]

As long as you have the whole DME harness, it's actually a piece of cake. All of the Motronic signal wires are in the DME harness, so it's just a matter of supplying power where needed. And with a 911 Carrera, the DME relay is part of the harness itself, so you don't have to wire it in separate like I did with the 944. I can get you a copy of the DME wiring if you need it.
I have the complete harness - engine compartment to DME, relay and altitude module. Any and all documentation is greatly appreciated. Never hurts to have too much information ... well, most of the time.