can I fry a relay without blowing a fuse?

[richardb, austin]

The 1st question:
If I had an intermittent short to ground on the hot wire to an aux drive light, could that blow the relay & not the 15 amp fuse that is in-line with the hi-amp supply before leg #30 (ie, between the relay & battery) ?
The details:
I installed & the lights worked as expected for a few moments anyway. Switch off, back on -> no lights. No power on the big amp output (leg 85 across from 30). Chinese product, I suspect intermittent relay, so I get another relay (yeah, it's Chinese too) and do the same thing with the same results (Einstein commented on that behavior). THEN, I notice that the hot wire to the right lamp is touching the engine block. There is melted insulation but not catastrophic to look at & wiring is still continuous at that point. The trigger voltage for the relay (from the switched yellow/black supply) works as expected - 12 volts on legs 86 & 87 when the key and light switch are on. At one point, the hi amp output was reading minus 12.8 volts (lights inoperative), but mostly it reads 0.0 vdc.
2nd question:
If indeed, I've somehow fried 2 relays, do I need to move the fuse so that it's between the relay & the lamps?

[gearheadfla]

Way over my head

[ekap1200]

Richard ;sounds like its wired wrong, terminal 30 is common to 87a and 87 with 87a being normally closed, and the output to your lamps should be 87. The field terminals are 86 and 85 . if your fuse is connected from the batt to terminal 30 and the output is shorted your fuse should have blown before you overheat the relays contacts. Gene K.

Do a search on adding electrical gagets here on the forum and there is a sketch of these bosch type relays and their connection terminal.

[Turbo4x4]

Richard,

While it is certainly possible to fry a relay before a fuse blows, as Gene stated, it is VERY VERY unlikely, even if the relay is not rated for the amperage you're drawing. Look for miswiring. By the way, it is not uncommon for a direct short to ground to smoke the insulation on the wire without melting the wire itself. It all depends on the wire size and the rating of the fuse your have protecting the wire.

[ekap1200]

Richard, to avoid any confusion, on some brands of relays terminal 87A is sometimes marked as 86 and is normally closed to terminal 30. Hope this sketch helps.

[richardb, austin]

Gene (et al), Thanks for the tutorial & pictures. On both of these 30 amp relays I've tried, 87 is across from 30 & 85 & 86 are across from each other. 87A isn't there. I'm triggering with Y/W switched 10 amp supply at 85 & then to ground at 86. Hi amp supply from batt, thru fuse to 30, then out thru 87 to light switch, then to lights. As per your (& tech tips) schematic. I've done this before on both lights & horns, but I'm stymied this time. I'll get 'er.

[Turbo4x4]

Gene (et al), Thanks for the tutorial & pictures. On both of these 30 amp relays I've tried, 87 is across from 30 & 85 & 86 are across from each other. 87A isn't there. I'm triggering with Y/W switched 10 amp supply at 85 & then to ground at 86. Hi amp supply from batt, thru fuse to 30, then out thru 87 to light switch, then to lights. As per your (& tech tips) schematic. I've done this before on both lights & horns, but I'm stymied this time. I'll get 'er.

richardb,
Please don't take this the wrong way, but have you checked the grounding of your lights, or much less likely, the continuity of the light bulbs themselves? Since you didn't blow the fuse, and the relay appears to be working properly, it doesn't appear to be a short problem. These seem to me to be the only two possible causes for your problem.

[richardb, austin]

Good point Turbo, but I have effectively checked the ground. I jumpered across the relay from pin 30 to 87 & the lights come on. I'm sorry if I implied that the relay is working properly. It's not & neither was the relay before it. I've gotta check my wire routing AGAIN!

[Turbo4x4]

10-4, richardb. Hope you're back lighting up the highways soon.

[richardb, austin]

The subject line question has been answered: Yes I can (blow a relay etc). I removed & replaced all wiring on the aux lights & finally found the short. No, I don't know why I blew relays (plural) instead of 15 cent fuses. New relay w new wires -> a-ok. See ya next month.