Like many on these boards I have a non-working heating system on my 2008 GL1800 (VII A). The grips and seats are all out. I have followed the trouble shooting guidelines in the manual and I am at the end of the guidelines (and my rope). The manual says "Replace the heater control unit with a new known-good one and recheck". My problem is finding a known good one. Local service/dealers are not helpful. Even from the factory I cannot be certain the part is good. (STUFF HAPPENS!) So is there anyone out there that lives near Sacramento CA that has a known good unit that I can plug into my bike?
I've not heard of many failures with the heater control unit. Many faults seem to be related to grip heat element failures, which causes the heater control unit to go into a fail-safe mode.
39305-MCA-A71 looks like one on eBay (used) for ~$40 as a backup plan.
Luck to ya!
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The left grip heater is the usual culprit. The printed heat circuit in the grip gets twisted and broken with improper technique putting the bike on the centerstand, thus twisting/flexing the grip and breaking the element in the grip.
The seat and grips are in a series wire circuit and if one of the grips is out or the seat is unplugged or cut wire, none will work.
Thanks. The grips read resistance exactly as indicated in the shop manual. One of the front thermistors in the seat is twice what the other one is (144 Ohms Vs.72.3) I think I could get a 72 ohm resistor and find out how to jump that one thermistor and trick the system to definitively find the culprit. But I don't yet know how to sire that external resistor.
My Shop manual indicates that at 15C (garage temp) the resistance should be 72-80 ohms. One of the front thermistors read 72.3. I think that one is OK. It is the one that read 144 ohms that worries me. Does anyone near Sacramento CA Have the time and willingness to let me plug their saddle into my wire harness? That would nail it down for sure.
More Throttle wrote: ↑Thu Feb 06, 2020 2:48 pm
My Shop manual indicates that at 15C (garage temp) the resistance should be 72-80 ohms. One of the front thermistors read 72.3. I think that one is OK. It is the one that read 144 ohms that worries me. Does anyone near Sacramento CA Have the time and willingness to let me plug their saddle into my wire harness? That would nail it down for sure.
You said the one that is at 144 worries you. For good reason...it doesn't meet the allowed.
If it is the left grip??? You didn't say what it is.... You have to unplug the grip connectors and check each grip resistance.
newday, I have checked all resistances in all components. The only one one of spec is that one thermistor. The solution is "replace the seat". So before I do that I'd like to plug in a saddle that works and verify my theory.
and I am at the end of the guidelines (and my rope). 
The manual says "Replace the heater control unit with a new known-good one and recheck". My problem is finding a known good one. Local service/dealers are not helpful. Even from the factory I cannot be certain the part is good. (STUFF 
HAPPENS!) So is there anyone out there that lives near Sacramento CA that has a known good unit that I can plug into my bike? 
