Quote:
Originally Posted by kerry
Can someone explain the advantage of replacing the original relay when replacing the loop plugs with pencil plugs? I couldn't see why it was necessary.
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In our case the biggest motivation was the fact that the entire new style kit (relay, plugs, and wiring) was cheaper than just the relay for the 77 (ours failed on, frying a couple plugs too).
I figured the new style relay was required to run the pencil plugs, but perhaps the old relay can be made to work. To install the new relay I had to run four wires to the old relay location to tap into the existing wiring (ignition switched power, output to glow plug light, ground, and I forget the last one, probably starter). In the engine bay I got to ditch the old resistance wires for the series-wired loop plugs, and run a power wire directly to the battery (via fuse) for the plugs.
The new relay does not use the temp sender in the head, it uses the ambient air temp of the engine compartment (ie where the relay is) to determine how long to glow after starting. As I understood the system, our original 77 relay didn't glow after starting. That alone made a big difference.
For us the benefit was the combo of the more effective and reliable pencil plugs, more advanced glow plug controller (afterglowing), and the fact that the whole kit cost less than replacing the original relay and a couple melted loop plugs. Honestly its been the most beneficial hour or two I spent working on the car.