Need some advice

[Jeff in W.C.]

Hey guys,
I need some advice. I posted a while back about fitting a post 91 wiring harness to my 88 R100 RT. I found out that the post 91 is a direct fit for the one in my 88. However, it would require purchasing a new fuse box. The new wiring harness has the wiring harnesses connected to three fuses with one unused, and the newer blade style fuses are used. The wiring harness on my bike has only two fuses. Unfortunately, I don’t know how the circuits are broken down—that’s a little bit above my head. BMW divided them into three circuits for a reason, but there doesn’t seem to be a lot of problems with them two circuit harnesses.

Both pre 91 and post 91 wiring harnesses are available; however, replacing the harness with the newer one would cost an additional ±$60. So is it worth an additional $60 to have the wiring harnesses broken down into three circuits versus two?

P.S. I found a definition of advice once, suggesting that advice is what you seek when you know the answer, but don’t like solution.

[Ken in Oklahoma]

I don't have the two different wiring diagrams to compare, but on the surface I would say save your money. What you have with your 2 fuse setup works (unless it didn't work and that's why you need a new wiring harness). In other words, if it ain't broke, don't fix it.

As far as BMW having a reason, they had a reason a long time ago (say about 1976) to incorporate more than two fuses into their wiring harness--and they didn't. To fuse each different electrical function in a reasonable manner would take a lot of fuses, not just 3.


Ken

[John Falconer]

Jeff, Please remind us why you are considering replacing the harness - was there a short that burned off some insulation? John

[dougie]

Jeff, I dug out a later wiring harness from my electrical stash and it has the fusebox as you described (3 x spade + 1 spare).
If it is any help, I checked the wires in and out -

Fuse 1. grey/black x 2 -------------------------grey
Fuse 2. green/black x 2 .......................green
Fuse 3. red/white...............................red

(The fuse 3 wires are heavier gauge than fuses 1,2)

[Airbear]

Jeff, I dug out a later wiring harness from my electrical stash and it has the fusebox as you described (3 x spade + 1 spare).
If it is any help, I checked the wires in and out -

Fuse 1. grey/black x 2 -------------------------grey
Fuse 2. green/black x 2 .......................green
Fuse 3. red/white...............................red

(The fuse 3 wires are heavier gauge than fuses 1,2)

I've just been fiddling around with the wiring on my R90 and re-drawing my (altered) harness.

Fuses 1 and 2 are the traditional ones and both appear after the ignition switch -

Fuse 1, grey to grey/black, covers the parking light, instrument backlights and the tail light.
Fuse 2, green to green/black, covers power to brake light, indicators, idiot lights and horn.
Fuse 3 on that fat red wire will come before the ignition switch and will kind of cover everything. It is a very sensible addition, but you can simply add an aftermarket blade type fuse holder - the type with good fat wires hanging out each end - to do that.

I believe it is best fitted on the fat red wire between the diode board and the starter relay. This puts it before the connector board and thus covers the ignition and lighting power. The best physical location is tucked up right near the starter relay under the front of the tank. It needs to be easily accessible, so a bit of slack in the wires is suggested.

[Jeff in W.C.]

Jeff, Please remind us why you are considering replacing the harness - was there a short that burned off some insulation? John

My neutral light is intermittent, and I kind of like having it functional. The problem is in the main plug to the instrument cluster. In my asking around and searching the forums, I did not get the impression this could be fixed. It also gets me wondering if something else is about to give me trouble. So, I figured the easiest way was to replace the harness.

[Duane Ausherman]

Jeff, I would never replace a harness with only that symptom. The intermittent could be related to something else. Test it first.

I would run an outboard wire between those two points and see if the light works properly. Basically, you are just replacing that one wire. If indeed the wire in the harness is bad, then you have a choice to use the "extra wire" that you jumped in (save work and money), or (spend money and time) replace the harness.

Rule #1, keep your money in your pocket........... or mine.

[Deleted User 62]

Jeff, Please remind us why you are considering replacing the harness - was there a short that burned off some insulation? John

My neutral light is intermittent, and I kind of like having it functional. The problem is in the main plug to the instrument cluster. In my asking around and searching the forums, I did not get the impression this could be fixed. It also gets me wondering if something else is about to give me trouble. So, I figured the easiest way was to replace the harness.

Before giving up on the plug, look at the connectors and you will see that each male pin goes into a sort of rolled metal tube on the female side. Push something between the rolled tube and the switch body to try pinching the tube a bit for better contact. Another possibility, put a small bit of aluminum foil in the hole to make better contact between the pin and the tube. If that doesn't work, do what Duane says and run a wire to bypass the plug.

[Jeff in W.C.]

Jeff, Please remind us why you are considering replacing the harness - was there a short that burned off some insulation? John

My neutral light is intermittent, and I kind of like having it functional. The problem is in the main plug to the instrument cluster. In my asking around and searching the forums, I did not get the impression this could be fixed. It also gets me wondering if something else is about to give me trouble. So, I figured the easiest way was to replace the harness.

Before giving up on the plug, look at the connectors and you will see that each male pin goes into a sort of rolled metal tube on the female side. Push something between the rolled tube and the switch body to try pinching the tube a bit for better contact. Another possibility, put a small bit of aluminum foil in the hole to make better contact between the pin and the tube. If that doesn't work, do what Duane says and run a wire to bypass the plug.

I'm pretty much convinced that the connection between the wire and the rolled tube is severed.