S4 tachometer/headlight issue

19-02-2017, 02:31 PM

Help needed please
S4 at tickover all ok
Switch on headlight at tickover and tachometer needle drops to zero
Blip throttle tachometer reads fine
Switch off headlight at tickover and needle picks up again
Any ideas chaps
If answer involves checking stuff please keep it simple
I'm a bit thick where electrics are concerned
Thanks in advance

Nickj · 19-02-2017, 08:38 PM

The clocks are the electronic units with no mechanical drive getting the signal from the ecu.
So the stepper motor isn't stepping with lights on but is with lights off which sounds like it will be a bit of a nightmare to trace.
It could be something gross like the voltage available lights on/off but that's probably too simple but you could check at the battery and main fuse what happens. The volts at the fuse ought to remain the same.
The sender is actually the timing pickup(s) with, AFIK, the information sent to the clocks from the ECU. it is possible that a component od the ECU has gone bad or there is a dry joint but not sure how you'd test that ... There might well be something available if you hook up the ecu to some diagnostics software that would at least show this isn't the case. There are a few strands on this I think.
Another possiblity is a component on the clock control board either gone bad or having a dodgy joint. These, the resistors etc, are all surface mount components and difficult to check.

Start with the simple power supply when the lights are on and off. After that you're going to need some specialist input.

alan s4 · 20-02-2017, 06:58 AM

I had the same symptoms with my S4.

The tacho would only register when revs were increased, at tickover it either wouldn't read or would be erratic.

Problem was linked to Reg/Rect.

Easiest test is to check the voltage from the battery terminals when the bike is at idle, if it's less than 14V then you have issues.

If the reg/rect is faulty then you will usually have problems starting.

Darren69 · 20-02-2017, 07:18 AM

This is often caused by a flat or nearly flat battery, so reg/rec could be suspect. Check voltage across battery when engine is running should see it increase as you rev engine to about 14 volts, if good.

19-02-2017, 02:31 PM	#1
manx999 Guest Posts: n/a	S4 tachometer/headlight issue Help needed please S4 at tickover all ok Switch on headlight at tickover and tachometer needle drops to zero Blip throttle tachometer reads fine Switch off headlight at tickover and needle picks up again Any ideas chaps If answer involves checking stuff please keep it simple I'm a bit thick where electrics are concerned Thanks in advance

19-02-2017, 08:38 PM	#2
Nickj Too much time on my hands member Join Date: Jun 2007 Location: Forest Of Dean Bike: S2r Posts: 3,189	The clocks are the electronic units with no mechanical drive getting the signal from the ecu. So the stepper motor isn't stepping with lights on but is with lights off which sounds like it will be a bit of a nightmare to trace. It could be something gross like the voltage available lights on/off but that's probably too simple but you could check at the battery and main fuse what happens. The volts at the fuse ought to remain the same. The sender is actually the timing pickup(s) with, AFIK, the information sent to the clocks from the ECU. it is possible that a component od the ECU has gone bad or there is a dry joint but not sure how you'd test that ... There might well be something available if you hook up the ecu to some diagnostics software that would at least show this isn't the case. There are a few strands on this I think. Another possiblity is a component on the clock control board either gone bad or having a dodgy joint. These, the resistors etc, are all surface mount components and difficult to check. Start with the simple power supply when the lights are on and off. After that you're going to need some specialist input. __________________ "The final measure of any rider's skill is the inverse ratio of his preferred Traveling Speed to the number of bad scars on his body." Song of the sausage creature

20-02-2017, 07:18 AM	#4
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,022	This is often caused by a flat or nearly flat battery, so reg/rec could be suspect. Check voltage across battery when engine is running should see it increase as you rev engine to about 14 volts, if good. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

20-02-2017, 06:58 AM	#3
alan s4 Registered User Join Date: Sep 2013 Location: Glasgow Bike: S4 challenge Posts: 447	I had the same symptoms with my S4. The tacho would only register when revs were increased, at tickover it either wouldn't read or would be erratic. Problem was linked to Reg/Rect. Easiest test is to check the voltage from the battery terminals when the bike is at idle, if it's less than 14V then you have issues. If the reg/rect is faulty then you will usually have problems starting.