New wiring harness install advice needed

I have bought new headlight and main wiring harnesses for my '74 MkIIA from RGM to replace my melted original harness and I am looking for advice from those of you who have done this before. I have been looking at the bike (sitting in my warm dining room without tank and seat) for three months trying to decide just how to start the job. And since winter will soon be gone, I'd like to get the job done before riding weather arrives in Chicago. For me the harness replacement is somewhat complicated by the fact that I am color blind... So should I start at the headlight and work my way back to the tail light just unplugging the old harness and installing the new as I go or is there a better method or sequence to follow? I have a Boyer and a Podtronics R/R installed so I know I will need to do some minor changes to the harness to accommodate them as I did when I installed them years ago. Any insight that will get me going is greatly appreciated.

Terry

flyboy49 said:

I have bought new headlight and main wiring harnesses for my '74 MkIIA from RGM to replace my melted original harness and I am looking for advice from those of you who have done this before. I have been looking at the bike (sitting in my warm dining room without tank and seat) for three months trying to decide just how to start the job. And since winter will soon be gone, I'd like to get the job done before riding weather arrives in Chicago. For me the harness replacement is somewhat complicated by the fact that I am color blind... So should I start at the headlight and work my way back to the tail light just unplugging the old harness and installing the new as I go or is there a better method or sequence to follow? I have a Boyer and a Podtronics R/R installed so I know I will need to do some minor changes to the harness to accommodate them as I did when I installed them years ago. Any insight that will get me going is greatly appreciated.

Terry

Click to expand...

I did mine and I am color blind as well. My daughter helped me with the colors.
Before you start ripping the old one out, I laid mine out on the bike and arranged the loom so I could straighten it out to the way the old one was.
I then cut the old loom on both sides where it passes thru the frame leaving everything still connected.
I pulled out the cut parts and passed the new loom thru the holes and then systematically hooked up each wire, one by one until I got each section done.
I started at the rear first.
I first cleaned the old wiring with lacquer thinner so I could see the real colors. And with the help of my daughter I got it done in no time.
Being color blind sucks, Having a daughter help me, priceless!

I did my MK2A last summer, I started at the battery tray and first went to the rear cutting out the old harness as I went, I then did the battery area and then went forward to the big connector and then did the headlamp harness. Dealing with the changes made for the Boyer was easier as I left all the old connections in place until I had the new harness in position. The old harness was in 4 pieces when I was finished.

I guess the first thing I would do is take a whole lot of pictures of the current motorcycle wiring harness while it is still installed in the bike. This information may be useful when reinstalling the new harness. Then I would completely remove the whole harness.

As for your new harness have someone help you with the color identification as Guido suggested. Then using masking tape and a pen label each wire as to its color/s and where it goes if you happen to know. When I rewired my motorcycle I used aircraft wire so basically all of the wire's are colored white. So I was kind of in the same boat. I labeled every wire with its factory color code and purpose at each end using masking tape. For the final labeling of the wires I made the labels using a label maker that prints on shrink tubing. The shrink tube labels were installed before crimping on the terminals. You may consider doing the same, however you would need to cut off all of the bullet and spade connectors, install the labeled shrink tube then reinstall new connectors. The nice thing is that once it is done it makes future troubleshooting a lot easier.

Also I would suggest getting a multimeter. It is a useful tool.

Peter Joe

The original harness was designed as a drop-in harness, as most production harnesses are. There is no need to duplicate its design, just run the new wires point-to-point on the bike, with the tank removed and the air filter in place (that space is crowded wire-wise, and you'll need to leave room to remove the filter). You can run harness bundles on BOTH sides of the tank if you want. For my MK3, I designed the new schematic first, then wired, and then constructed the new harness diagram, although Kommando's technique is a bit faster and less prone to error. In any case, you'll need to document the work with a new harness diagram. You can keep all of the original wire color codes with new wires from British Wiring. However......

If you plan to convert to negative ground, or even think you may in the future, now is the time to correct the color code. Feel free to keep the hot wires blue-brown (all new aftermarket devices will use RED as the hot wire, but there is no confusion with both wire codes employed), but all ground wires in your new harness MUST be black, or you'll be forever confused as to the meaning of a red wire. Retain WHITE as the switched hot wire. The taillight housing, horizontal frame piece just aft of the battery caddy, and the headlight shell are all good common grounding points, employing the frame as a redundant ground system.

Remove the old harness first; you can, certainly, try to lay the new harness over the old, but I have found this to confuse the issue; the harness, really, only fits one way and it is much easier to "thread" the new harness through the various grommets with no obstructions.

OK, so the new harness is on your motorcycle, now you need a wiring diagram and a multi meter. If you get a queasy feeling looking at all those lose ends you are not alone. Just like curing world hunger it can't be done in one swoop, but rather by one circuit at a time. I like to start with the directionals, but begin with any circuit, the horn is popular just because it is the first component to be fitted, again it doesn't matter. one by one with continuity testing, and before you know it you're done. Doing the task one circuit at a time also gives you the opportunity to do neat wire routing so you don't end up with a hornets nest of twisted intertwined wires.

When you think you are done place a 3-5 amp fuse in the fuse holder and see if it holds (key off), replace that with a 10 amp and turn the key to the first position which energizes the ignition circuit and offers power to the horn, directionals and brake light, activate the horn, directionals and brake light individually, if the fuse keeps its cool replace it with a 15 amp fuse and test the headlight (high/lo). If you are still above water install a 25 amp fuse and test as many circuits, simultaneously, as you can, if no issue pat yourself on the back and go for a ride.

Do make sure that the harness isn't in a position anywhere on the motorcycle where it can abrade or burn and that you have cable-tied it securely. And just a side note: if the cable ties aren't tight enough they will act as cutters.

As with any endeavor a positive attitude and confidence will go a long way...

Bill.

flyboy49,

Since you are using a Podtronic reg/rec you will probably have a lot of extra wires in the loom. I would suggest that you wire the alternator directly to the Podtronic and from your Podtronics to the battery. The only thing I can think of is you might have to tap one alternator lead to drive your assimialtor (if you still have one). I am also guessing you have gotten rid of the capacitor also. Take your time and good luck.

Pete

Thanks for all of the advice and good ideas. I think I will try and tackle the job on Sunday. The wife will be around to help with wire colors should I need it. Taking a bunch of pictures first and then starting at the battery tray and working to the tail light, cutting out the old harness and reattaching the new as I go along, seems the most logical and foolproof method of attack to me. No "loose ends" that way. After that's done I'll start working towards the headlight. Wish me luck.

Terry

And as its a MK2A the harness run is different to pre MK2A's as the flasher unit moves inside the battery area leaving that area free to take the plastic tool tray. They had fitted my harness wrongly at the factory and the plastic tray would not sit properly, it does now. So the legs for the rectifier, rear brake switch and the flasher unit are the battery side of the rear plate.

Terry,
Since you will be taking everything out now might be a good time to install a relay for the horn. I placed mine in the battery box area. You can even keep the original horn wires intact and attach them to the relay. Head light relays might net be a bad idea either. Something to consider.
Pete