Several years ago, I noticed that the radiator cooling fans (all three of them) on my Lotus Esprit S2 seemed to be operating at suboptimal speed. With a fiberglass-bodied car, this problem is often caused by a dodgy ground connection. Since there's no handy metal chassis to find, it's necessary to run ground wires everywhere -- which is how the factory designed the harness.
I found that the voltage was low, but all the grounds checked out. Checking this was much easier said than done. When I searched for the fan control relays, I found them nestled up under an inner fender. To assure that the relay wasn't damaged by a seized fan bearing, each relay had been duly equipped with its own fuse.
So far, so good. The fuses were all good. In checking them, however, I noticed that they were the European style, consisting of a ceramic mandrel with a die-cut piece of copper over it, forming the fuse element and the two contacts.
This is a simple two-part solution to the four-part (plus solder) design used in period autos -- a ceramic or glass tube with a fusible element and two end caps. But the fuses themselves were not the root of the problem. It was the Lucas relay-cum-fuse holder.
The fuse holder consisted of two rather stiff brass tabs protruding from the top of the relay, with holes in them designed to cup the pointed ends of the fuse. The trouble was there was little to no spring to the tabs. Thus, once a fuse was installed, it was inevitably a little loose. A firm contact was nigh impossible to achieve with the combination of marginal design and poor choice of materials. So, with use and time, the already dodgy connections degraded, and voltage at the load was compromised.
Since the relays were in a hard-to-see location, it was easy to solder the short pigtails of an inline fuse holder to each of the tabs and put in a proper fuse. The fans experienced a remarkable rejuvenation of operation, moving at least twice as much air and doing a proper job for the first time in years.
This entry was submitted by Peter Blackford and edited by Rob Spiegel.
Peter Blackford is a graduate of Worcester Polytechnic Institute and works as a design and applications engineer with Cable USA in Naples, Fla.
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