Fusing the Overdrive Circuit

[rlich8]

Hi All,

I plan on fusing the overdrive circuit when I (correctly) hook it up within the next few days. The previous owner of my car did not hook up the overdrive properly nor fuse it.

Can someone let me know where is the best place to fuse the circuit?

Thank you!

Roy

 

[rlich8]

Oh! and what amp fuse?

 

[TR3driver]

I put my fuse in the supply to the relay, near where it is connected to the ammeter. I used an MDL 8 (8 amp, "slow blow") as I happened to have a case of them; but I believe that even an AGC 5 would do.

Unlike most fuses, in this case my main intention was to protect the solenoid itself. Hopefully now, if my solenoid gets hung up so the internal contacts don't open, the fuse will blow and give me a chance to free or repair the solenoid before the pull-in coil burns up. Hence the fuse is quite a bit smaller than the wire sizes would indicate.

The OD fuse holder is just visible at the top of this shot:

 

[rlich8]

Excellent! This is exactly what I was looking for - thank you!

 

[Geo Hahn]

On mine I installed the fuse at the relay using a little homemade harness that connects to the existing spade connectors. I too used a slo-blow but perhaps a standard fuse would work as that line only sees the high current of the solenoids pull-in coil for a brief moment.

 

[hondo402000]

what vehicle do you have, on my TR6 both brown and white wires attach at the fuse block. Brown is always hot but not fused, white is a switched hot and not fused either, I guess it depends on which side of the fuse block you attach the wires as to weather its fused or not, but originally they are not fused.

Hondo

 

[rlich8]

I have a 1966 TR4A, I think I will fuse it at the ammeter like the first poster suggested.

 

[TR3driver]

originally they are not fused.

That is exactly right, and true of the earlier TRs as well. There is even a comment in the Laycock manual about how it "should not" be fused since the fuse might fail and disengage the OD, which could overspeed the engine.

Oddly enough, though, Triumph did use a fuse in the OD circuit on Stags.

But having had a solenoid ruined because the cutout contacts didn't open, apparently just because a bit of rock worked it's way in and jammed the plunger, I like having a fuse. The solenoids are cheaper now, but at that time they were around $150 (closer to $200 today allowing for inflation), and I didn't want to lose another one.