Gremlins

[79beem]

Hello All,
 After replacing my bent ( P.O. ) handlebars, strange things are at large in my wiring.

1- Hazard light switch blinks when indicator turned on, indicator dead.  ( unplugged hazard switch - problem side stepped )

2- At >3500rpm - (A) Indicators don't work
                          (B) Tacho becomes erratic
                          (C) Rev.Limit warning blinks wildy
                          (D) Headlight intensity fluctuates
                          (E)  High-beam indicator light flickers

Learn how to use a multimeter?

[tvrla]

When multiple electrical faults happen like this, a good rule of thumb is to check the ground connections.

[Justin B.]

Put a ground strap between the frame and your forks and see what happens...

[Bob_Roller]

Check the forward ignition coil mount for cracking, it has the main grounding or earthing point for the entire electrical system on the '78-'80 year bikes .


When it cracks, it causes odd electrical problems like yours .

[nhmaf]

Indeed - this sounds like what one would expect with an intermittent ground - perhaps some wires were strained/pulled/broken in the process of bending the handlebar, and now that you've straightened it and readjusted the wiring harness, the final parting of the conductors has occurred.

[79beem]

Hey all,
thanks for the responses.

Spot on with the Coil bracket theory, its broken.
Neg battery lead worn through to wire against frame.

I taped battery lead,cable tied coil to frame,extended ground wire to rear coil mounting bracket.

Now the bike only fires on one cyl.

??

I can try another ground point, but I'm interested why this has happened, or why any alternative point may do the same.

[nhmaf]

Do you have a multimeter>

You may have dislodged a wire connection from one of the coils while dealing with the broken bracket, or it could be that the bracket's failure hastened the failure of a coil.   Or, you may have not fully fastened one coil or the other such that isn't making a good connection..

First, the easy test - try swapping the spark plug end connections between the left and right cylinders - does it only run on the other cylinder now?   IF so, then you've at least isolated the problem to the coil and/or spark plug lead.   You can then do some more swapping, visual inspection and you can use your multimeter to check resistances.   If you are running with points ignition then the primary side of each coil should be between 3 ohms and 5 ohms.   The secondary sides of the coils varies from mfgr and year, but a simple check is to leave the spark plug leads connected to the coils and just pull the spark plug end caps from the plugs.   With one multimeter probe in each plug cap you should measure the series resistance of both plug wires and coil secondaries - the total resistance should be somewhere in the 22000 ohm to 50000 ohm range.  If it is much less, or much more, then you've a bad lead or coil secondary.

[Barry]

If you are running with points ignition then the primary side of each coil should be between 3 ohms and 5 ohms.  

I know that you really know this nhmaf   it must have been a typo.

The twin 6 volt coils on points bikes have a nominal primary resistance of 1.5 ohms each making 3 ohms total in series.  Mine measure 1.5 ohms near enough spot on, not that it is very easy to measure low resistance values with any great accuracy.

I measure 23,000 ohms plug cap to plug cap which with 5000 ohm caps makes the secondaries 6500 ohms each.  As far as I know they are correct values for original Bosch 6V coils.

[nhmaf]

Oops, yes, I was confused with another motorcycle and coil set on the primary impedance- thanks for correcting it!  

I have also seen some other coils used (they weren't Bosch) with higher resistance secondaries, for a total plug cap -to-plug cap resistance of around 32K, and they worked OK, but were likely for some other automotive application.

[79beem]

Happy new year Chaps.
Now, the bikes been running fine since my last post.
Seems I dislodged the high tension lead.
Thanks for all the help.