Short fuse keeps blowing

[Ulf]

Hi, I recently noticed my heater fan wasn’t blowing and that the car was really hard to start, which pointed me towards the short 25a fuse powering both. I finally got hold of a handful of them, but they keep blowing every time I try to start the car. What could cause that?

[Chris Long]

Bad starter solenoid or starter?

[Ulf]

Starter works fine, engages and turns - and if I override the fuse (yes I know I shouldn't...), the car fires right up. As far as I know, the stubby 25a fuse is only for the heater fan and the CSV - so would the starter solenoid even have anything to do with it? A hate electrical issues :-/

[WRe]

Hi,
fuse 6 (25A) feeds directly (see wiring diagram: https://www.sl113.org/wiki/Electrical/WiringDiagram)

  5 heater blower switch --> 12 heater blower motor
20 time switch (230 SL) [or relay for automatic starting aid (280 SL)] --> 31 electromagnetic starter valve and 32 thermo time switch
21 relay for automatic starting aid (230 SL) [or relay for mixture control (280 SL)] --> 21 time switch and 33 magnet for mixture control

In each of these components could be a short-circuit fault.
If you bypass fuse 6 and the engine starts I would assume your fault in the heater blower switch or heater blower motor first of all.
I would disconnect this heater blower switch first.
Does the fuse blow when you turn on the ignition or when you start the engine?
...WRe

[Ulf]

When I turn on the ignition, the heater fan starts blowing just fine, but as soon as I crank it to start, the fuse blows :-)

[Chris Long]

I’d be careful of jumping the fuse. goofle seems to indicated failing starter solenoid with a short in coil.

That makes sense to me as starter motor would engage but with reduced current as the solenoid is pulling lots. 

[66andBlue]

Ulf,
try to bypass step 2 on the ignition switch by jump starting. Attach one lead to the + pole on the battery and the other to the “G” terminal (the smaller of the two terminals) of the thermo time switch to engage the starter. The procedure is described here in Figure 3 with photos: https://www.sl113.org/wiki/Restricted/ValveAdjustmentTour
If the fuse doesn't blow then the trouble is in the ignition switch.

[Pawel66]

Sorry for putting in my 2 cents...

Blowing of the short fuse is irritating also because they are in short supply... Please do not play with jumping that fuse. I would rather connect two wires to the terminals of this fuse in the fuse box and place a different type of fuse, same amperage between those wires (holders for this kind of fuses are available in many automotive stores). This is to create work space.

Do not tighten the negative battery terminal as you work on this. Put the terminal on the battery post only when you are doing the test.

If you say the fuse gets blown when you turn the key to the starter position, then that is where I would look for shorts.

The following circuits/devices are energized when you turn the key to starter position (may vary from car to car, so you may want to adjust it):
- ignition switch
- starter solenoid
- cold start relay (or two relays next to each other)
- back up light/safety switch if your car is automatic
- this is circuit 50

1. I would start with visual inspection of the wires and connections. Particularly the wire that goes to starter. If this is ok, next step I would do is to
2. Disconnect both cold start relays and try to crank the engine. If the fuse blows, what is left to check is the starter, ignition switch and back up switch, all the cold start aids are eliminated.
3. Remove the plug from back up switch and jump two pins marked 50 on the plug side (both should have two wires each) if you are not sure which ones are those, write here, we will show you. Try cranking. If the fuse blows, you are left with starter and ignition switch.
4. You may follow the advise of Members in other posts here to determine if it is a starter or ignition switch. You can also detach the wire from the starter and turn the key - if the fuse blows, it is most likely the ignition switch.

I am not writing about measurements with ohmmeter as there are coils there and the short may not be with 0 ohm, so this would be confusing, I think...

[Ulf]

Thanks to all of you, great input - will try them all soon and keep you posted. :-)

Br

Ulf

[ejboyd5]

Save yourself much aggravation and the cost of many blown fuses during the diagnostic process by wiring a resettable circuit breaker in place of the 25 amp fuse. I actually keep a small kit containing several circuit breakers of different sizes along with two leads with alligator clip ends for just such a situation.

[Ulf]

@ejboyd5 - good point as I only have 4 left out of the 6 that I managed to source, I have ordered a set of small wires with clips on each end and I already have a bunch of modern fuses that I plan to use for testing :-)

[66andBlue]

Few years ago when I started to test the Bosch horns I ran into the same problem, blew more short 25Amp fuses than I could buy.
Decided to buy a circuit tester with an automatic circuit breaker reset and never looked back. The Power Probe company makes several models I have model III with all the wires and connectors:
https://www.amazon.com/Power-Probe-PP3LS01-Red-Circuit_Testers/dp/B007QV0R7W/.
https://www.ebay.com/itm/Power-Probe-3-III-W-PPLS01-LEADS-PP3LS01/293362878507
https://www.powerprobe.com/product-comparison

Several other members here have one.

[WRe]

Hi,
does anybody has any experience with these simple resettable circuit breaker
https://www.ebay.de/itm/12V-24V-Inline-Auto-Leistungsschalter-Circuit-Breaker-Reset-Schalter-30A-/293104028324?_trksid=p2385738.m4383.l4275.c10&redirect=mobile ?
...WRe

[Ulf]

Ok, I have been fiddling around a bit with my very limited skills.
When I insert the fuse and switch the ignition on, the fan blows fine - only then I turn the key to engage the starter, it blows.
When I turn off the fan before cranking, fuse blows too - wouldn't that leave out the heater switch as the culprit? Or can it still cause a short even when not turned on?
I tried disconnecting the CSV at the inlet manifold, but the fuse still blows, so that can be left out too - or what? (see pic)
There are three different relays at the left side of the engine bay - my guess is that the black one (see pic) is the relay for the starter?
Also, there is an uninsulated wire running to the fuse box - my guess is ground, and it has always been there - at least for my 13 years of ownership (see last pic). Last year the ignition was changed to Lumenition electronic ignition within the original distributor, the original coil (the red Bosch) and pre-resistance is still present, could that be causing this all of a sudden?
I'm still going to try the trick of circumventing the ignition switch, but I'm waiting for some wires to do this - due in the mail.

Br

Ulf

[Chris Long]

I'm still with a short in the starter solenoid coil...

[Ulf]

here's the second pic, can only upload them separately :-)

[Ulf]

And the last one ...

[WRe]

Hi,
Alfred made a nice picture which describes the relays you are asking:
1 Relay for automatic starting aid
2 Relay for wiper motor
3 Time switch
The uninsulated wire in your picture looks very strange and doesn't belong to the car.
Even a turned-off fan switch can cause problems.
...WRe

[Pawel66]

I would forget the fan for the time being, especially that you say it works and fuse blows when you turn the key for starting.

That eyelet on the wire might have been touching the manifold causing short...

Disconnect the black square relay, see what happens.

I obviously do not like that wire...

[Ulf]

Update - I've spend some time today trying different things out. The odd uninsulated wire didn't go anywhere, so I removed it - didn't make a difference. Tried disconnecting the black square relay/solenoid, this time the fuse didn't blow - but the CSV didn't engage either. Are they somehow connected? I will certainly replace that relay to begin with as they are not that expensive.
Oddly enough - my small set of cables used to test without sacrificing the small fuses (made from unobtainium) didn't work - tried with a regular 15A and 25A fuse. When I hooked it up, the heater didn't blow and the car wouldn't start either - and the test fuse didn't blow. One end of the cable got really hot though. Weird ...
Anyway, I will keep you updated, and again - your help is greatly appreciated :-)

[Pawel66]

I, actually, fail to understand why the device with a different fuse is not working... would have to take a look how you hook it.

If you are saying that when you disconnect the cold start relay, then the engine cranks and the fuse is not blowing - then you might have identified the circuit where you have a short.

Yes, CSV will not work when that relay is disconnected - this relay is managing the CSV work, provides power to it.

I would have hoped you looked at the wiring diagram and visually inspected all wires and connections.

Connect the relay back to the wires.

I believe you did the exercise of disconnecting the wire from CSV and fuse was still blowing (I hope the wire connector was not touching the inlet manifold - from your picture I see it could - so you may want to make sure) then it is not the CSV coil that causes the short.

If the fuse does not blow, hook it back together. Then disconnect wires from the solenoid on the FIP (if you have it). Try cranking. If the fuse does not blow - it is probably that solenoid that causes the short. If it still blows, connect back the solenoid.

As the next step I would suggest remove both wires from TTS. Make sure the removed wire connectors do not touch anything. Try cranking and see if the fuse is blowing. If not - there is something wrong with the TTS. If yes, connect it back.

The next suspect is the relay.

Alternatively: you may take the car and printed wiring diagram to the electrician. You can start the car in the following way:

1. keep the black square relay disconnected
2. Jump a wire from + (e.g. that blowing fuse place) to CSV - but have someone touch the CSV connector only when you are cranking, maybe a couple of seconds longer. Remove this wire when engine started.

[Ulf]

@Pawel66 - I'll try to answer your questions as good as I can :-)
I, actually, fail to understand why the device with a different fuse is not working... would have to take a look how you hook it.

That's beyond my understanding as well, have even tried different wires/fuses. Drilled out the brass bit that prevents the normal long fuses to be used to test with these instead, which works (heater blowing)

If you are saying that when you disconnect the cold start relay, then the engine cranks and the fuse is not blowing - then you might have identified the circuit where you have a short.

Exactly - a new cold start relay is on its way from Germany

Yes, CSV will not work when that relay is disconnected - this relay is managing the CSV work, provides power to it.

Good to hear

I would have hoped you looked at the wiring diagram and visually inspected all wires and connections.

I have inspected all wires and connections, no fraying, loose ends or wires that touches something it shouldn't - diagrams are Chinese to me, I'm a creative in advertising and technology is not my force (I can write a song about cheese in half an hour, though...)

Connect the relay back to the wires.

Done

I believe you did the exercise of disconnecting the wire from CSV and fuse was still blowing (I hope the wire connector was not touching the inlet manifold - from your picture I see it could - so you may want to make sure) then it is not the CSV coil that causes the short.

Yes, it didn't touch the manifold, moved it out of the way

If the fuse does not blow, hook it back together. Then disconnect wires from the solenoid on the FIP (if you have it). Try cranking. If the fuse does not blow - it is probably that solenoid that causes the short. If it still blows, connect back the solenoid.

That I haven't tried, will do that first chance

As the next step I would suggest remove both wires from TTS. Make sure the removed wire connectors do not touch anything. Try cranking and see if the fuse is blowing. If not - there is something wrong with the TTS. If yes, connect it back.

Stupid question, what's the TTS?

The next suspect is the relay.

Alternatively: you may take the car and printed wiring diagram to the electrician. You can start the car in the following way:

1. keep the black square relay disconnected
2. Jump a wire from + (e.g. that blowing fuse place) to CSV - but have someone touch the CSV connector only when you are cranking, maybe a couple of seconds longer. Remove this wire when engine started.

Good to know, thanks - really sorry that I'm not more mechanically minded. I'm going to a Pagoda meeting this Wednesday and will discuss the matter with more skilled people (than myself, not you). Your help is greatly appreciated even if I might seem like a tech moron to you :-D

/U

[Pawel66]

At least you are a good copy writer. I am neither a good copy writer, nor electrician nor mechanic... On copy writing I usually was on the other side of the brief...

On the fuse device try to use lower amperage fuse - 15A or 20A. If the wire is getting hot, you have a short there. Short fuse was blowing, the other fuses do not - the amperage may be somewhere on the edge.

Always remove battery - terminal when you work with wires.

If you disconnect things, e.g. solenoid, make sure the wire ends do not touch anything.

TTS - Thermo Time Switch. This is the device that feels the engine temperature and tells the relay and CSV that the engine needs additional fuel to start. It activates the relay to give power to CSV.

It would be good if you understand how the cold start aid works: https://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour

This also shows how the TTS looks like and where to find it (depends on the car you have).

What I am trying to describe is to go through cold start aid components (CSV, relay, solenoid on FIP, TTS) that are activated during cranking. This is because when you switched it all off - the fuse is not blown.

It may be the relay itself, of course. Just replace it when you get it and see.

Given the fairly low level of experience of both of us - I keep thinking maybe show it to a pro or more experienced colleague. Maybe start the car on Wednesday and go there to show it.

[lpeterssen]

Dear Ulf

I see that you have made many many many test. Pawel66 has helped a lot and many other members.

Looking at the wiring diagram which you say is Chinese for you as you are a creative media guy, makes me conclude that there is no direct relationship between fuse no.2 clients and T50 signal which is the cable which you energize every time you crank the engine.

T50 signal is only related to a fuse no.6 clients, but in that case is also impossible a direct connections as T50 signal Is only on the low current side of those relays.

You said that by removing square black relay the problem stopped. As that relay does not take current on its high current side from fuse no.2 but from fuse no.6 that means with NO DOUBT that T50 cable insulation on the branch the goes to the right side of your car is broken for some time, it made a short and melted some other cables.

To solve your problem You need to service your wiring harness. It needs an urgent restoration. Remember that T50 signal cable (2.5 mm) non fused, you are on risk of fire.

I have plenty of experience on that. Contact if you need a good Engineer that understands and love this cars.

Regards
L.peterssen

[Pawel66]

Thank you!