|Tonti Key Switch Relay Fix by George Dockray
Here's an easy fix for a number of electrical gremlins that arise from dirty & worn contacts in the key switch on the 850T, LM1 / 2, T-3, SP, etc.
Over time and use the contacts in the switch get dirty & worn. The original design sends all the battery and alternator output to the electrical components through the key switch. As the switch contacts wear this causes a voltage drop and resistance across the switch of as much as one volt. This causes dimmer than normal lights, starter solenoid engagement problems, and a general misalignment of the humors - electrical-wise.
A quick, cheap & easy fix is to install a standard type 30 amp relay (one for fog lights works fine) to carry the electrical load from the battery - alternator to the load and use the switch to merely ground the control circuit to the relay (a matter of milliamps that even dirty contacts can handle easily).
The diagram below shows the set-up. My version combines the brown (fuse block), green (parking lights) and white (ignition) leads so there is no separate parking light function since I never use it anyway.