bypassing igntion box?

[Mark DiSilvestro]

A friend has a '72 W115 gas 220. Last week the ignition system died. Car has a transistor ignition unit under the battery tray, triggered by points. Got the wiring diagram and traced the initial problem to a burned out ballast resistor that supplies voltage to the transistor ignition box. Replaced the resistor and car ran OK for about 10 minutes then died. Restarted several times but wouldn't stay running. New resistor got extremely hot but hasn't burned out yet. Suspect transistor box is shorting out, but my factory W114/115 manuals have no diagnosis info on the transistor unit and I've heard a new OE transistor box may cost several hundred dollars. I've seen numerous posts about retrofitting Crane and Pertronics electronic ignition kits, but has anyone simply converted one of these to the pre-1970 ignition setup, without the transistor unit? I was told many years ago that this can be done, but the ignition coil would need to be changed, as the one used with the transistor box is hotter and would quickly burn up the points. I believe the coil ground would have to be switched by the points, instead of permanently grounded for the transistor circuit and coil positive fed through one of the resistors. Any suggestions and recommendations would be much appreciated.
Thanks.

Happy Motoring, Mark

[dieseldiehard]

Originally Posted by Mark DiSilvestro

A friend has a '72 W115 gas 220. Last week the ignition system died. Car has a transistor ignition unit under the battery tray, triggered by points. Got the wiring diagram and traced the initial problem to a burned out ballast resistor that supplies voltage to the transistor ignition box. Replaced the resistor and car ran OK for about 10 minutes then died. Restarted several times but wouldn't stay running. New resistor got extremely hot but hasn't burned out yet. Suspect transistor box is shorting out, but my factory W114/115 manuals have no diagnosis info on the transistor unit and I've heard a new OE transistor box may cost several hundred dollars. I've seen numerous posts about retrofitting Crane and Pertronics electronic ignition kits, but has anyone simply converted one of these to the pre-1970 ignition setup, without the transistor unit? I was told many years ago that this can be done, but the ignition coil would need to be changed, as the one used with the transistor box is hotter and would quickly burn up the points. I believe the coil ground would have to be switched by the points, instead of permanently grounded for the transistor circuit and coil positive fed through one of the resistors. Any suggestions and recommendations would be much appreciated.
Thanks.

Happy Motoring, Mark

Search?
Yields: Wiring around transistorized ignition box
and my 220 with no OE transistor box:
1971 220

[meltedpanda]

Hey mark
Dunno if it will help but I got an ignition box on the parts car, as well as the coil, its a 73 W114, Looks to have different connections than my W115, but if you think you could use it let me know. I assume it is working

[Mark DiSilvestro]

Thanks. I'm looking to keep this fix as simple as possible.
If it comes down to a bad transistor box, I'm looking to eliminate it by converting to a straight points ignition, which will probably require a new coil and ballast. My 1970 W114/115 service manual has absolutely no info on the transistor ignition, but my '76 W114/115 body-chassis manual does give wiring diagrams for both the transistorized and non-transistorized ignitions. According to them, I'll need a 1.8 ohm ballast resistor to go with the non-transistor Bosch coil. If a new Bosch coil proves too unavailible or expensive, I'm willing to go with a pre-electronic ignition Ford or Chevy coil, but may have to use the matching Chevy or Ford ballast.
Any suggestions from someone who has bypassed one of these by changing to a straight points setup?

Happy Motoring, Mark

[cth350]

keep the box or upgrade to a cranes. The box does a nice job. You can open it and replace the transistor. There used to be instructions for the job on www.mbz.org. Hopefully, it survived the crash.

Just get a used box. There's at least one on ebay for 25$. Note that there are three different boxes out there for 1968-73 cars and two boxes after that (at least). The mid-70s boxes have a coax connector wire with big black plug. You don't want that one. The earlier boxes use screw fittings on a terminal strip (like yours).

If you find the same basic box (with the oval plug), but a different part number, post the number and I'll tell you how to wire it in place. A 300sel 3.5 is an example of wiring different from your W114, but I forget the other varients off the top of my head.

All three varients are listed in the 3.5/4.5 service manual BTW.

-CTH

[dieseldiehard]

I highly suggest a Crane optical or Pertronix magnetic conversion as long as you are going to fix er up and drive her, that will make you happy for years to come without any concern over "tune ups" - granted the transistor box is fine, when I converted mine to a Crane CD ignition I gained performance, better acceleration with no hesitation and better fuel mileage. Best $$ I ever spent on a gasser! and its going on three years with no changes at all. I might have to look at the plugs someday

[Mark DiSilvestro]

Well, I do have a '72 W114 'parts car', at least for testing purposes, but eliminating the transistor box with a coil and ballast transplant would be much easier than wrestling with two transistor boxs, under two rusty battery trays, that have been subjected to 34 years of moisture and battery acid. I took some ohm readings on my friend's ignition coil and will compare them with the 'good' coil on my parts-car tomorrow. Meanwhile, my friend is having some medical problems and isn't using this car much right now, so we're trying to limit expenses, if possible.

So far, while everyone here appears to be sold on the various OE or aftermarket electronic ignitions, I have no complaints with the point setups on the various pre-electronic cars that I've owned over the years.

As for a used transistor box, I'd rather not gamble on another one that's been sitting under a battery tray for over three decades. I'm trying to basically 'rationalise' this ignition so that we're not dependant on a transistor ignition module, OE or aftermarket, that may cost several hundred dollars and not be readily availible. Anyway, I WILL ask my local supplier for his price on a new OE transistor box.

Happy Motoring, Mark

[cth350]

A new box is over 300$. You really, really want a used one. -CTH

[Mark DiSilvestro]

I didn't say I was actually going to BUY one. I really, really want to eliminate any $$$$ box.
Why shoudn't I just convert to a straight point ignition, like that already in hundreds of thousands of vintage cars on the road, including my Fintail and most pre-'70 Mercedes?

Happy Motoring, Mark

[nhdoc]

Originally Posted by Mark DiSilvestro

I didn't say I was actually going to BUY one. I really, really want to eliminate any $$$$ box.
Why shoudn't I just convert to a straight point ignition, like that already in hundreds of thousands of vintage cars on the road, including my Fintail and most pre-'70 Mercedes?

Happy Motoring, Mark

The only reasons are because the electronic retrofits generally are maintenance free, higher energy for easier starts and more reliable than conventional points. They are not all that costly ($100 or so for the kit) and if you want the car to be as reliable as it can be they seem to accomplish that. The time it takes to install is about the same as installing a new set of points and condensor. If you want to simply install a condensor and use conventional points and coil that will certainly work OK and be cheaper than the upgrade, but we've all dealt with corroded or burned points and the electronic upgrade kits eliminate this as a future problem.

[Mark DiSilvestro]

Well here's the results of my ignition bypass research.

New OE transistor box list price $1300 - OUCH!
My price about $800 - Still OUCH!
No OE rebuilt availible.

He also has availible an aftermarket Pertronix electronic kit for $188 list, not including the recommended replacment ignition coil

OE Bosch coil, ballast, points and condenser to convert to pre-'70 non-electonic ignition about $120
(Might save about $40 if I get a non-Bosch coil & ballast)

Did a quick Forum search but didn't find prices on Crane or Pertronix. Did find that some had problems fitting Crane trigger wheel or getting unit wired or timed.

Before I condemn my friend's transistor box, I'm going out to my parts car to inspect/remove the coil so I can eliminate the one on my friend's 220 as a suspect.

Happy Motoring, Mark

[Arthur Dalton]

Lot's of guys just use a standard coil and put the 2 resistors from the Transistor unit in series from ign sw to coil . Then you are stock ignition...although I prefer the Crane XR700 unit , part 0231.
they can be had for less than $100 and work flawlessly.
Pert is hall effect and Crane is Optical..

[Mark DiSilvestro]

Total for the two resistors in the existing system is 1.0 ohm but my W114/115 wiring diagram calls for a 1.8 ohm resistor with the non-electronic coil. Whatever we decide, nothing will be done that isn't reversable.
I'll update on the final ignition configuration.

Happy Motoring, Mark

[Arthur Dalton]

It all depends on the coils primary R factor.
What you are looking for is approx 3 omh with coil and ballast.

The most common problem on the Transistor switchgear set-up was not the gear , but rather the condenser .. they could be eliminated as they did not funtion as a regular point condenser dies..if one seee burnt points on the SW setup, it usuaally has a bad condenser....

[cth350]

red bosch coil get 1.8 ohm resistor (has red band)
black coil gets 0.9 ohm (gold band)
blue coil gets a 0.6 & 0.4 ohm (one's ble, one's silver; I forget which is which).

On some w114 cars, one resistor is barrell shaped and doesn't have a band. I kinda recall it being equivalent to the blue one. Don't quote me. -CTH