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.
FYI,
Nick Kemp
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