what does the hot-start relay do?

[BBShriver]

Pelican part BOS-WR1

What exactly is its function and how does it work?

I'm trying to resolve a (very) intermittent non start issue on my car (90+ percent of the time it works flawlessly, but the other it acts like there's not even a starter connected, no click, clunk, whir, or anything just nothing... but I can still hear the fuel pump, CDI, all lights work etc)

I've ordered the new hi-torque starter from Pelican, whether or not it's the root cause, I figure my 1973 starter is due for a replacement anyway.

I'm thinking of ordering the $90 ignition switch as a potential fix/preventive maintenance. Just curious about this relay kit.

[Wilhelm]

Sure it is not just a bad ground or intermittent connection in the starter circuit?
Sometimes on my 71 911, I get similar symptoms. Turn the key to"start" position and nothing. I found dirty/corroded fuse contacts on the fuse block in the engine compartment. Cleaned the fuses and contacts and everything is good. Might check grounds, fuses, etc. Cheap and easy to do.

[BBShriver]

That is something I want to do as well, but just trying to go ahead and replace the "usual suspects" as part of the 38 year maintenance.

[Walt Fricke]

"No click" means the starter solenoid isn't working. Which could be because it is old and sticky. Or because electricity isn't getting to it. So the troubleshooting list for this starts with seeing if you have 12V showing up at the solenoid, and working backward. Or you can see if you have 12V coming out of the starter position of the itnition switch, and work backward or forward depending. I don't recall there being a fuse in any of this, but haven't checked the circuit diagram (but you should do so - this very Pelican website has diagrams you can use, even if not one for '73s).

You'll like the smaller, lighter (and much newer) geared high torque starter, so that's a small upbrade even if nothing was wrong with your 38 year old Bosch. Why couldn't Bosch have made fan blower motors which were as durable?

[Wilhelm]

Originally Posted by Walt Fricke

"No click" means the starter solenoid isn't working. Which could be because it is old and sticky. Or because electricity isn't getting to it. So the troubleshooting list for this starts with seeing if you have 12V showing up at the solenoid, and working backward. Or you can see if you have 12V coming out of the starter position of the itnition switch, and work backward or forward depending. I don't recall there being a fuse in any of this, but haven't checked the circuit diagram (but you should do so - this very Pelican website has diagrams you can use, even if not one for '73s).

You'll like the smaller, lighter (and much newer) geared high torque starter, so that's a small upbrade even if nothing was wrong with your 38 year old Bosch. Why couldn't Bosch have made fan blower motors which were as durable?

I should have mentioned, my 71 911S has MFI. When I have had no start/no "click" symptoms similar to the original posters I have found that cleaning the fuse contacts and fuse block contacts (3 of them) back in fuse block III in the engine compartment solved the problem. I have found that a lot of intermittent electrical problems like turn signals, tail lights, parking lights , etc not working are usually the result of dirty or loose connections somewhere. I agree about replacing the starter if it is in your budget. I know I am on borrowed time with mine !

[911pcars]

Adding a relay to the starting system ensures full battery voltage is being applied to the starter solenoid so it can energize as designed. Normally, source voltage is supplied by the ignition switch via the yellow wire. However, along with a borderline battery (or not), there could be voltage drop caused by oxidized/loose connections/contact points in the fuse box, switch, circuit and/or the longish 8-9' path from switch to solenoid.

Installing a relay closer to the starter results in a shorter path for the "yellow" wire. Voltage source is now via the battery cable that also powers the starter motor.

Hope this helps,
Sherwood
FWIW, Remote Starter

[Joe Bob]

Some people swear by it, some swear at it and call it a bandaid fix for other things that are wrong.

[Walt Fricke]

I'm in the band-aid camp. With good connections there should be no need at all for a relay to make the starter solenoid (which is also a relay) work properly.

This from a guy who for the longest time would crawl under his VW bus with a screw driver to connect the solenoid directly to the battery cable to kick the starter over so the regular starter switch would do its job. After a while I ran wires to terminals which were on the edge of the frame so I didn't have to crawl as far under with my screw driver.

I miss the old Bus, but not that part (rebuilt starter cured, of course).

[911pcars]

I must agree it is a band aid. For many, the crank position of the ign. switch wears out first. Fortunately, for owners of later 911s, the switch has sub-assemblies which can be replaced. In the case of early 911 switch assemblies, they're NLA. If a switch is found, they're in the $400+ neighborhood.

The modification linked in my earlier post adds a momentary switch and relay to crank the engine and thus reduce wear and tear on the existing switch.

Sherwood

[psalt]

Brandon,

If you take a took in the archives you will find that an intermittent starter is a common problem with the 911. There are several reasons for this, and the Bosch rebuilt starters also have a poor reputation because all the cores are old and the Bosch rebuild does not touch one of the problems. I have given up on the rebuilds and switched to the Japanese gear reductions starters. You have made the right choice. The hot start relay jumps the heavy starter positive cable to the yellow solenoid wire to by pass all the other wiring, switches and connectors. Do yourself a favor and install a $6 remote starter button in the engine compartment, like on the old Jaguar solenoid. If the switch, wiring, connection gremlin pops up you can start the car without crawling underneath. It also comes in handy for valve adjustments, compression tests, checking for spark, etc.

[T77911S]

the switch that paul talked about is nice to have for work, but i am with the others, i dont believe in band aides.

grounds are so oftern over looked when electrical problems come up. all connections need to be clean and tight.

if you have a car alarm, that can cause start problems too.

you can rebuild the starter yourself, including parts of the solenoid, but soldering is a must.

you need to verify 12v on the yellow wire, with it connected and while starting the car but in the non start condition.

[BBShriver]

Yep, and the problem as was discussed the last time I brought this up is that the problem occurrs so rarely that there's no way to "be prepared" for failure when it does happen to be able to test.

For a few reasons I don't believe it's the battery itself (new battery, and when it works it works perfectly with no hesitation)

Since it's such an intermittent problem I'm just trying to go through and replace all the common failure parts. The electric portion of the switch looks like $90 from Pelican, I am inclined to order that as preventive maintenance as well, and would like to add the start switch as mentioned.

For the engine mounted start switch, what current does it need to run? And where do I get such a switch?

[psalt]

Brandon,

My advice would be to hold off on replacing other parts until you get the gear reduction starter. The battery is always the first thing to test with a starter problem because of the high current draw and the voltage drop over the long wires. I have seen several Bosch starters that intermitently fail unless the battery is fully charged. If you have not done it already, it is a good idea to clean the battery terminals, ground post and ground strap. If you have CIS injection, be aware that the cold start valve is spraying every time you hold the key in start and in my experience the thermotime switch safety is not quick enough to prevent flooding. Any auto parts store should have a universal starter push button. You then just need to put a ring terminal for the battery cable and a spade for the yellow solenoid wire. On a front engined car it is usually easy to jump the solenoid at the starter and test the wirings and switches from above. On the 911 you need to raise the car and crawl underneath to access the wiring which can be a problem if you are wearing your shooting outfit.

[BBShriver]

I already replaced the battery and ground strap, and cleaned up the + terminal wire thinking that could be the root.

[tobluforu]

This same thing happened to my 72 years ago. After replacing the batteries, the ground straps, cleaning what I could I then bought a rebuilt bosch starer. This worked great for about 6 months and the same thing started happening again. I then applied the band aid and never looked back until that rebuilt starter failed last year. At this point I replaced it with a high torque starter, removed the band aid and all has been well since.

[BBShriver]

Just a general question... Why isn't this "band aid" considered a design improvement? It seems like even if everything else is working perfectly this relay should still be more reliable than the factory set up?

Or is the relay known to introduce its own set of problems?

[Joe Bob]

The relay masks other problems. As mentioned there are no NEW Bosch starters. They are all remans that aren't like new. They simply get them so that they work but typically fail on hot start.

The best defense is having a local shop replace with new all known failure parts.....more expensive but a more reliable starter.

[RoninLB]

Originally Posted by BBShriver

For the engine mounted start switch, what current does it need to run? And where do I get such a switch?

I use a marine Cole-Hersee momentary switch that has silver contacts rated max 35 amps in engine compartment, but sometimes listed as a 20 amp sw. No relay required

If you feel a 10 amp momentary sw is good enough search West Marine # 270884. It has pre-attached 18 ga wire and is completely waterproof

I looped a 10 gauge marine wire from starter battery lug to engine compartment and back to solenoid. I used Waytek Inc, Home page to buy fuses, circuit breakers, cable ties, wire and other electrical supplies By Waytek Inc. polyolefin double wall shrink tube to cover the wires. All connectors were silver soldered


COLE HERSEE Switch at West Marine

[911pcars]

With a typical 25A Bosch-type relay doing the switching, the circuit only requires a light-duty switch to control the relay which performs the actual current switching to the starter solenoid.

If you opt for a remote switch and no relay, use a switch designed for starting and larger gauge wires as shown in Ron's post (equivalent to the West Marine switch).

Sherwood

[Walt Fricke]

When your ignition switch starts to fail in the starter position, you can just wire in a momentary on pushbutton switch in parallel with the key switch to power the starter solenoid. Like the switch Ron pictured. Here is one looking like it belongs. I still use the key first, because occasionally it works and I have to turn it at least to the run position anyway.



It even fits the decor.

Relays are nice if you have voltage drop issues, or want to control current with lighter duty switches and wires. However, I had a standard relay fail on me at Sebring this year. It was the ordinary multi-prong 25 or 30A relay readily available at auto parts stores (not the round Porsche one), and one of the coil wires broke off where it was soldered to the prong which stuck up through the plastic casing. Given the finer than a hair gauge of these enameled coil wires, it is hard for me to imagine how it worked up the inertia to fatigue and fail. But it did. i suppose it didn't have quite enough slack between the solder joint and the coil, and perhaps the coil wiggled enough. A failed relay coil was not my first thought, so finding this took a bit of time. I think, for a race car anyway, that it may be useful to minimize the use of relays where you can.

Walt