Fuse blew on Chrylser Reg/Radio Shack Mod

[650Fool]

I did the Chrysler/radio Shack mod to my otherwise stock '77D. The system has been working great. Today I went to run an errand. The bike started right up and while I was waiting for the oil to get where it was needed, noticed my headlight indicator light was still on (I also did the indicator rewire that lets me know when the bike is no longer charging - THANKS to those who devised this, did it, and posted what a good idea it was!). I checked the basic connections, then checked the 7.5A fuse on the brown wire to the regulator. It was blown. I had no spare, so I put a 10A microwave fuse (a real "ceramic" one!) and ran my errand. The bike ran great, the fuse didn't blow, and there was no smoke or smell from any wiring. I will replace the fuse with another 7.5 (and probably another, then another...), but I am curious as to what might have happened without having to tear the electrical apart indiscriminantly. The problem may or may not recur, but anyone have any ideas or experience with this? Thanks!

 

[Grinder]

I don't know what other fuses you have in your system but a 7.5 seems a little light. the brown wire typically feeds all the electrical on the bike. The stock main fuse is 20A.

 

[pamcopete]

650fool,

It's possible that the 7.5 Amp fuse was marginal, so the phenomena of thermal fatigue may have set in. Basically, what that means is that repeated cycles of current flow close to the rating of the fuse heats the fuse element up and eventually the fuse fails.

And... thanks form the appreciation of the headlight failure mod and the Chrysler / Radio Shack mod....

 

[650Fool]

Hello Grinder!

I have one main fuse which I believe is a 20A. That did not blow. When I did the Chrysler mod I added the 7.5A fuse as recommended. I think to protect the regulator from a runaway alternator, but now I'm not sure as it might have been to protect the system from a bad regulator. The brown wire was added and goes from the regulator to the black wire on the engine side of alternator harness (the black wire on the frame side was disconnected and insulated). Also, I normally ride with the headlight on, but it was off while the bike warmed up. The battery is fairly new and had a good charge.

Hello Pete!

I put in a new screw type holder with a new fuse, but it was from an electronics store so I don't know how long it sat on the shelf. The fuse was shiny. I did the mod and installed the fuse about 4 months ago and put about 120 miles on the bike since then. I assume that 7.5A is still the amperage you recommend, so I'll get another (and may be go to a blade type fuse), and see what happens. I was curious to know that if the fuse was doing its job what might have happened to cause it to blow.

THANKS for replying!