Relay in Starter Circuit?

[ejboyd5]

Does the 230 SL. the 250 SL or the 280 SL employ a relay in the starter circuit to activate the starter solenoid so that the full current required to activate the starter solenoid does not have to pass through the ignition switch?

[cfm65@me.com]

Hi EJ,
I don’t think so. The positive from the battery goes straight to the starter, therefor the starter gets full power anyway. The solenoid only closes the circuit and does not need a relay.
Regards
Chris

[lpeterssen]

Hi EJ,
I don’t think so. The positive from the battery goes straight to the starter, therefor the starter gets full power anyway. The solenoid only closes the circuit and does not need a relay.
Regards
Chris

Dear Chris:

The starter selenoid inside the starter, is a kind of relay. Starter is connected directly to battery as indicated by previous post and that selenoid passes the full battery power to starter motor and moves the spin wheel once it receives the signal T50 that comes from ignition switch. So the current trough this cable is not so high.  It is important of course to have good ground at starter and good and strong T50 signal; which implies to have a perfect uninterrupted conductor diameter 2.5mm2 (AWG14) from ignition tumbler to the Starter selenoid .

This particular cable has a very weak insulation that Softens with age.  It is recommended to change it.

In later cars as W108, you can observe that T50 cable from parking/neutral safety switch to starter  selenoid is no longer thick as on w113 and uses a much smaller caliber around AWG16. This means, that with time starter selenoid have become more efficient and therefore require less energy.

[ejboyd5]

Thank you for your responses so far, all of which are basically acurate. The question however is very specific. Was the Pagoda ever equipped with a relay in the circuit between the ignition switch and the starter solenoid so thar turning the ignition switch to the start position would  only trigger the relay with a current draw measured in milliamps rather than having the ignition switch directly activate  the starter solenoid which puts a current draw of 6 to 8 amps on the ignition switch. This use of a relay Is a common aftermarket addition for other cars of the era and I am wondsring if it was ever used in the Pagoda.

[lpeterssen]

Dear Friend

As far as I know after looking at many wiring diagrams the answer is NO.  it was not originally used a relay for that purpose.  But you can do it.  If you want an original look source a time period correct relay, find an auxiliary mercedes fuse box and make this conversion which for sure will reduce the stress on your ignition tumbler switch.  I think that a screw terminals relay will be better as you really need a secure connection for this particular service.  Let me post a picture.

Best regards
L.peterssen

[ejboyd5]

Thanks for verifying the lack of a starting relay in the Pagoda series.  I believed that to be the case since it followed Mercedes practice with the 190 SL and 300 SL, but I did not have access to all the Pagoda wiring diagrams to check.  Actually, I am involved with a project to retrofit a 300 SL in an effort to decrease the current required to be carried through the ignition circuit to activate the starter solenoid as part of an effort to preserve the original components and eliminate a fire hazard. Your suggestions relative to a period correct relay with secure terminals is attractive, but I am presently considering a modern Bosch relay for its reliability.  Whatever is done will be 100% reversible in case some future steward favors originality over everything else. 

[lpeterssen]

Dear friend

What you can do is to fit a modern Bosh ISO type  relay into and OLD BOSH RELAY SHELL, in that case nobody unless very very expert, Wil notice that the inner components of the relay are modern.


Regards
L.peterssen

[ejboyd5]

Thanks.  I've done exactly that several times with turn signal flashing units.