Guzzi OE heated grips not reaching full heat

Has anyone had experience of troubleshooting OE heated grips?  It's been a while since I've ridden the bike (1200 Sport "4V") in chilly weather, but I'm pretty sure I've not needed the maximum heat (3 bars) setting in the past.  These are the grips which plug into three connectors provided in the loom under the front of the fuel tank, and show up via an indicator on the dash.

The on/off/power button cycles the dash indicator from min-to-max okay, but even at max the grips only get mildly warm - with bare hands. The bike isn't giving any signs of electrical problems elsewhere.

Since the heat of each grip feels the same I wondered if it was the earth connection.  I separated and cleaned the plugs and sockets with switch cleaner, and tightened the female connector pins a bit.  Resistance to battery -ve terminal measures about a tenth of an Ohm at the loom earth for each grip, and I'm assuming that's not bad.  The grips each measure about 11 Ohms.  Is there anything else I can check?

Mine do the same thing. Being Italian, I just put it down to moodiness. I reality I know there is a problem but right now I really haven't got time.

I did start building a PWM controller to use instead of the dash - this project is also shelved for the moment.

Taking the tank off to do anything these days (going through separation - it's all good though) is a task I am leaving for later...

Haha, know what you mean about getting the tank off.  I seem to have got the knack of disconnecting the fuel pipe, but at times it would be handy if the pipe were longer so the tank could swing out to the side and rest on something while leaving the fuel connected.

I was wondering how the output of the dash to the grips might be tested.  Unfortunately I don't have a scope, but maybe an analogue volt meter might be able to show changes for each power level...?  Or if I could rig a 12V, 10W bulb across each of the loom connectors, would its brightness change with the PWM duty cycle i.e. heat setting?

Check the voltage that you are getting at each grip when running, but i think that resistance is over twice what it should be.
V/R = A so if you get 12v and they are 11 ohms you are only getting 1 and a bit amps per side.
As VxA=W that is only just over 12w per side - a bit chilly.

This site [You must be registered and logged in to see this link.] reckons that oxford grips give 40w per side and BMW ones 36w per side so you would expect a resistance of about 4 ohm

lcjohnny wrote:

Check the voltage that you are getting at each grip when running, but i think that resistance is over twice what it should be.
V/R = A so if you get 12v and they are 11 ohms you are only getting 1 and a bit amps per side.
As VxA=W that is only just over 12w per side - a bit chilly.

This site [You must be registered and logged in to see this link.] reckons that oxford grips give 40w per side and BMW ones 36w per side so you would expect a resistance of about 4 ohm

Interesting that comparison with other grips.  With each of my grips measuring 11 Ohms I made the assumption this was normal, but it does seem high compared with the other makes.  R&G's look to be 24W each side, so 6 Ohms.

Assuming it's PWM-based, I wasn't sure a simple voltage check would reveal much... unless for some reason it's low across all heat settings.  Maybe worth a check .

FlatTappeter wrote:

These are the grips which plug into three connectors provided in the loom under the front of the fuel tank, and show up via an indicator on the dash.

Is there anything else I can check?

Check the wires from the connectors that feed the grips to the frame.  You'll probably find a bit of corrosion there.  To be sure, add a hefty cable back to the negative of the battery.

kiwi dave wrote:

Check the wires from the connectors that feed the grips to the frame.  You'll probably find a bit of corrosion there.  To be sure, add a hefty cable back to the negative of the battery.

Thanks. I did notice the wires disappear quite quickly into the loom tightly wrapped in the usual cloth tape stuff, but couldn't see any scuffing through against the nearest frame part. Would it be necessary to dig into that bit of the loom to check further? And any ideas where the existing earth for the grips (blue wires) gets picked up from?