'78 /7 Insrument Cluster Lights & Tach Question

[shropdog]

I have a '78 R80/7 and looking for some input to fix a couple of electrical issues.

1) On the instrument cluster, some of the colored lights in the center of the housing (neutral indicator, high beams, etc.) stay on at all times even though the bike is in gear or low beams on, etc.. Anything specific I can look for?

2) The electronic tach does not operate....at all. I have not had it apart yet as I wanted to get some initial feedback as to what to look for. I hate to spend the $ to send it in for repair if I can fix it.

For what it is worth, the bike has 21k miles on it and did sit for some time.

Thanks in advance for any advice!

[20774]

You only mention two of the "colored" lights but also said "some" of them stay on. Are the two the only ones or are there others? The answer to that might result in a different response as to what's wrong.

As for the tach, I would definitely check to be sure that the wire off of the coil is attached. That's where it gets it's signal.

[shropdog]

Good point on the instrument lights....I will double check this evening (I "think" I know but want to make sure befor I report back).

Good tip as well on the coil wire for the tach...will check this evening and report back.

Thanks for the good info as my big 2" thick manual (not sure if it is Clymer's or ?) does not cover either issue.

[krehmkej]

That big multi connector can wiggle loose or the screw pull through the rubber. Mine even had a couple of dead bugs in there. Definitely make sure all this is clean and tight.

[shropdog]

I double checked the instrument lights and there is actually only one remaining on....the green turn signal on indicator. So....any thoughts on that one will be helpful (all turn signals work fine as does the annoying turn signal beeper).

I pulled the fuel tank, cleaned / plugged back in all of the coil wires / connectors one at a time....no luck....the tach still does not work. It may jump a bit when the bike is first fired up but, that is it (I think it is jumping from the vibration of the bike starting, not receiving an actual signal - if that makes sense). I did notice the tach needle is brittle as some of the sides on the needle are broken off so, I am starting to think the tach is just old.

Thanks again and any additional thougths will be appreciated. I have not checked the actual main connector at the back of the instrument panel but, will do so this evening.

[20774]

From this page:

http://www.omnilex.com/public/bmw78/78r100wire.jpg

It looks like the turn signals, hi-beam, speedo, and tach lights all share a common ground. Do these other lights work that you can tell? Obviously, these lights get power from a variety of sources.

The oil pressure light, charge light, brake light, and neutral light get their power from the same source...the starter relay. The ground switches for each of these lights is different, so it doesn't sound too likely that the ground is the problem. It must be power. And as suggested, it's probably the power coming into the block plug at the back of the speedo unit and/or the distribution of power within this plug.

Have you cleaned all the terminals on the starter relay? You were under the tank but focused on the coils. You might want to try and measure that you're getting 12v at pin 86 on the starter relay and also at the block plug at the back of the speedo...then go from there.

[shropdog]

Thanks again....all lights work in both the stack of lights between the gauges and the lighting within the gauges....the green turn signal light is the only one staying on. I will check / clean / test the starter relay terminal as suggested and the main instrument connector too. If no success, I will either not worry about it or take it to someone who knows alot more than I do (which obviously isn't much) about BMW electrics.

[tvrla]

There's a gasket between the bulb holder and the lenses that keeps the light from one bulb from lighting up any of it's neighbors. Pull the instrument cluster and check it, I'll bet you that's the problem.

And I agree, the multi pin connector to the gauges probably has a bad connection for the tach. Take a good look at it when pulling the gauges.