While trying to fix another problem, I noticed that sparks flew when a jumper connected to the cooling fan terminal touched the relay panel metal frame. To see how much current was there I touched one end of the wire to the fan terminal and the other to the bracket and enough current flowed to run the cooling fan.
I clamped on a meter and watched it as I moved stuff and it worked....I found the problem.
The trouble is that the metal jacket on the accessory relay went hot ... sometimes. It depends on the position of the internals (they move depending on how pressure is applied to the wires ... which can occur when driving). Once that metal housing is hot, the whole electrical panel goes hot since it is not grounded (which is probably good in this case since the 12Vdc source is not fused).
I checked the main relay and it sorta acts the same. When I move the wires, the meter readings jump around sometimes looking like they may have hit 12Vdc. That relay is the same type relay as the accessory.
For now the solution is to isolate/insulate the relay from the panel. An identical replacement may not be the best idea since it likely is prone to the same type of problem. A plastic housed relay is the better choice but it needs to have the current carrying capacity.
NOTE: this could be the reason for some electrical compartment fires. The power to those relays is a direct feed (non fused) from the battery (best I can tell from the diagram). So in the right condition where the hot relay exterior/panel touches a ground it could get very hot and "sparky" before it disconnects. From what I'm seeing, this should be a service upgrade! We need to find a suitable replacement relay where the housing cannot get electrically hot.
In the mean time it may be worth isolating/insulating the Main and Accessory relays.
Posted by: Nick Kemp <nkemp1165@xxxxxxxxx>
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