Blowing Fuses

[Joel]

I've just wired up a new set of gauges, and everything seems to work fine until I turn on the headlamps, at which point it blows the fuse. I think it's number 7 in the fuse box ('87 Sierra), the dash instrument fuse.

 

Prior to fitting the gauges the headlights worked fine, so why are they blowing the fuse and not the gauges!?

 

Is it likely I've just got some wires crossed somewhere, or would it be something way more complicated that I'll never figure out on my own?

[Guest Ant]

Remember that the dash lighting only comes on with the headlights, either dip, dim-dip, sidelights, or main beam. The number plate lamps also run from the dashboard lighting fuse on my loom ('89 Sierra). At a guess you're close to the limit with the bulbs on the dash, and the number plate lamps are the final straw.

 

Two options - either fit a dimmer to reduce the current draw on the instruments, or run a seperate line to some of the instruments.

 

Ant

[Joel]

Ok, now I'm *bleep* off. :angry:

 

I've completley stripped out all the new wiring to the gauges, so it's back to Sierra spec, and the headlamps are still blowing the fuse!

 

They worked fine for weeks before. All the bulbs are ok. Where do you start!?

 

Bloody wiring.

[Guest TerryBarry]

Gentlemen,

That's a 15A fuse in position #7 - this should supply 180 watts of lighting power - the number plate lights are 5w each.

I would look for a fault in the wiring somewhere.

Just seen your latest post - make sure that you are not somehow trying to pull the headlight feed from the instrument fuse

Terry

[Guest daveg]

Easy...

 

All you need to do is disconnect the fuse that blows, connect a multimeter, reading resistance to the non-live side of the fuse holder and earth, then switch on the headlight switch. If the resistance is below 15 ohms then you have a short or too many lights connected.

 

Start unplugging lights and connectors until you locate the short

 

(If you don't have a multimeter then buy one...) You could disconnect the battery to prevent yourself blowing the meter which could happen if its a cheap non protected one...

[Guest daveg]

Correction. Resistance for 15A = just under 1 ohm. I would think a correct reading would be around 5 ohms maximum.

[Longboarder]

If your donor was a late 87 then apart from panel and switch illumination, number plate lights and possibly rear fog light, fuse 7 supplies feed to dimmer B relay then switching current to dimmer 11 and the main and dip relays. Power goes to the head lamp main and dip bulbs through fuses 1234 but is supplied unfused from the + busbar.

First assemble a pile of 15 amp fuses! Then I suggest you pull the dim dip relays and the headlamp relays. Check the fog lamp switch and all other switches are off, and try the side lamps. Then switch on ignition + side lamps and head lamps. The head lamps won't come on of course but this tests the column switch. Flick to dip and main. Then fit dimdipB relay and repeat. Then dimdip 11. Then either dip or main relays testing as you go. Note the point the fuse blows and you have narrowed it down somewhat. Also try the rear fog and see if this blows it. If you blow fuses with just the sidelights then I would think one of the Grey/yellow panel light feeds is connected wrong or shorting.

It may then be obvious or post results.

 

Nigel

[Joel]

Thanks for the help guys.

 

I've not been able to test anything properly yet as my multimeter has chosen the perfect time to stop working (dropping it on the floor probably didn't help ), but I've disconected absoloutely everything that wasn't already there and it's still blowing the fuse.

 

A few other thoughts - Could it be the column switch? I temporarily wired up the wiper motor today and that didn't work properly either, yet it works fine if I connect it straight accross the battery.

 

Also I noticed the sidelights are still working after the fuse has blown, but none of the other light settings do.

 

How do you figure out the purpose of each relay? They're all nicely numbered, but I can't find a table or list in the Haynes explaining what each one is/does.

 

Cheers.

[Guest TerryBarry]

Have a look at Steve Loat's "Slimming down the Sierra's Loom" under Build Tipz on the main RHOCaR site. This gives an excellent listing of fuses and relays.

In the Haynes Manual the relays are listed with their code letter in the listing of components -

e.g.

70 Engine Management Relay XI

 

- in the fuse box there will be the Roman Numeral XI moulded next to where that relay plugs in.

 

Terry

[Longboarder]

Joel, 87 was a model changeover year and the early 87 loom and fuse arrangement is very different to the late 87. Can you tell what loom and fusebox you are using. i.e. if your donor had dim dip, ABS I think its a late 87.

Where did you take the feed from for the lights for your new instruments? Did you remove the sierra instruments and separate out all the wires to go to your new dials?

And yes it could be the column switch but that would be bad luck if you haven't changed its wires.

Sorry to answer your question with more questions but I'm unclear what you are dealing with here.

Nigel

[Joel]

Hello again,

 

You've probably gathered by now I don't have a clue when it comes to wiring

 

Nigel, I'm fairly certain it's the later 87 model. The fusebox has the space for ABS etc, and it was the revised front-end model (new headlamps etc).

 

I did remove the Sierra instruments and seperate out the loom for the new instruments. The feed for the dash lights is a grey/green wire, and the ignition switched live feed for the gauges is a black/yellow wire.

[Longboarder]

Yes. 87 onward.Unlikely to be the panel/switch illumination circuit or the column switch. Have you wired in all the dimdip stuff. If you have do your headlights run to earth or a brown/green wire back into the loom. Favourite is still identifying the relays 34 & 35 (Diag 2. Ext Lights Chap 13-page 40 in Haynes) and the grey/yellow wire connecting them, testing them looking for a short to ground.

 

Nigel

[Joel]

I'm really struggling here

 

I've disconnected every switch, light, gauge, even things that have nothing to do with the lights like the heater and screen washer bottle. I've completely removed the headlights, all the relevant relays, and I've even fitted a new column switch, and I've tripple checked every wire, but it's still blowing the fuse! :angry:

 

I'm using the Sierra fuse box un-modified, and I've not touched the grey/yellow wires that connect relays 34 & 35. How should I be testing them? I've identified the pin on each respective relay that the grey/yellow wire connects to - should there be a specific voltage there or something?

 

As I said before, the lights had been working fully (main, dip, sidelights etc) for several weeks before. Obviously I don't know the exact point they stopped working, or more to the point what I did that stopped them working, but I'm certain I've reversed every change I had made since I realised the problem.

 

The only other thing I can think, which probably isn't even related, is that when I used to connect the battery there were several clicks from something in the fusebox, and a small spark at the negative battery lead. It doesn't do either anymore.

 

Thanks again for any suggestions.

[Guest SteveL]

Joel

 

I've got lots of annotated Haynes wiring diagrams at home which I can send to you via e-mail. I put them together when I was trying to find out what the problem was with my headlights (when I had no working dim/dip).

 

When I get home tonight, I'll put some notes together and send them off to you. See if they help.

 

Steve

 

PS. Definitely get a new multimeter!

[Longboarder]

Joel trying to think through the possible fault is v. diff. without the car and I can't work out a logical fault in fuse 7 circuits. I now doubt that it is the dim/dip relays as they are powered when the sides are on but the heads switch them out of circuit. It may be some odd reverse feed going on.

Logicaly the fault occured when you changed the wiring to remove the donor panel and fit separate instruments. You now feel that all circuits are back to how they were. Are you confident that you have attended to each wire you moved and that they are back where they should be. If so something you moved has fried a component, switch,relay,fuse or wire which is causing the overload in 7, possibly by short or by setting up an errant circuit. You have tried swopping column switches. Did you swop both? Get a new multimeter. Make up two leads with female connectors on the ends and connect to the battery out of the car and remove and test all the relays to ensure they do what the pictures say they should. Can you check ALL the fuses in the fuse box for continuity and check them electricaly not just by eye.

 

Nigel