Starter Relay Upgrade

[RogerK]

I've done the MAD ammeter bypass and upgraded to a squareback alt. Next for me is the headlight relays. I already have relays for the EFI and fuel pump and I'll probably switch the horn to a "bosch" type relay and clean up the firewall some. My fuse/relay box has extra relays so I can power much more.

What about using a "bosch" type relay for the starter relay? I mean a complete under hood rewire is the plan so why not move the starter relay into the fuse/relay box?

Thoughts?

 

[67Dart273]

You could do that but I'd prefer not. Having that relay up there "can" be "pretty damn handy"

If you need a good place to hook your timing light, emergency work light, whatever, there's battery right there on that stud

If you need to bump the engine over for whatever reason, there's that relay, right there

To me, "seeing" a Mopar starter relay under there is as native as "seeing" an actual Mopar engine in there.

 

[RogerK]

You could do that but I'd prefer not. Having that relay up there "can" be "pretty damn handy"

If you need a good place to hook your timing light, emergency work light, whatever, there's battery right there on that stud

If you need to bump the engine over for whatever reason, there's that relay, right there

To me, "seeing" a Mopar starter relay under there is as native as "seeing" an actual Mopar engine in there.

I agree with the look of the Mopar relay having that "Native" look to it, and it is convenient to kick the motor over with, but for a timing light or work light I just use the battery terminals.

Since its not a restoration and the coil/ignition box is already on the inner fender having it appear 100% stock isn't a worry, I may leave it and run the other power taps back to the fuse/relay box.

Thanks 67Dart.

 

[BillGrissom]

I did (search for post "Modernized Engine Wiring"), using one relay in my Jeep relay/fuse box. See post. Wire the high-side of the coil (86) to your yellow "start" wire and the low-side (85) to your neutral safety switch. Newer cars (my 96 Voyager, probably 90's V-8 Mopars) use a standard 30 A relay to actuate the starter solenoid. Indeed when it won't start, pull the relay and jumper 30 (+12V supply) to 87 (to starter solenoid) and the starter should turn or at least clunk. Actuates even if tranny is in gear, so don't pin yourself to the garage wall.

I stripped everything off the firewall to de-rust and paint and liked the clean look w/ no wire clutter.

 

[RogerK]

I did (search for post "Modernized Engine Wiring"), using one relay in my Jeep relay/fuse box. See post. Wire the high-side of the coil (86) to your yellow "start" wire and the low-side (85) to your neutral safety switch. Newer cars (my 96 Voyager, probably 90's V-8 Mopars) use a standard 30 A relay to actuate the starter solenoid. Indeed when it won't start, pull the relay and jumper 30 (+12V supply) to 87 (to starter solenoid) and the starter should turn or at least clunk. Actuates even if tranny is in gear, so don't pin yourself to the garage wall.

I stripped everything off the firewall to de-rust and paint and liked the clean look w/ no wire clutter.

Thanks, Bill. I had drawn a schematic before posting that is exactly as you described. Two questions.
1) should I fuse the battery #30 side of the relay or the solenoid #87 side of the relay or does it matter?
2) what amperage fuse?

 

[67Dart273]

Be careful using Bosch style relays. Some of them have a built-in diode across the coil for protection of the switching circuit. You can easily check this with an ohmeter. If it shows coil resistance with your meter leads in one direction, and a very low resistance with the leads switche around, "there's a diode" in there.............

The below is SPDT (single pole, double throw, so it has a normally closed contact

The diode is at far left. The way it's wired you MUST have positive power on 85, and the "ground side" on 86



Also, not all these relays are wired by original bosch convention. Some of them have what amounts to dual contacts wired to a total of 4 pins, for larger current capacity

 

[RogerK]

Be careful using Bosch style relays. Some of them have a built-in diode across the coil for protection of the switching circuit. You can easily check this with an ohmeter. If it shows coil resistance with your meter leads in one direction, and a very low resistance with the leads switche around, "there's a diode" in there.............

The below is SPDT (single pole, double throw, so it has a normally closed contact

The diode is at far left. The way it's wired you MUST have positive power on 85, and the "ground side" on 86



Also, not all these relays are wired by original bosch convention. Some of them have what amounts to dual contacts wired to a total of 4 pins, for larger current capacity

Very Good info on the relays. Thanks! :cheers:

 

[BillGrissom]

Standard practice is that terminal "30" is 12 V supply and "87" is output. That is for "normally open" contacts, meaning "apply current to coil to actuate relay". Occasionally, one wants "normally closed" operation, in which case you use the "87a" terminal, but it is rarely wired if you look at a relay box in modern cars, and indeed some relays are missing the "87a" terminal (especially newer half-size type). It hardly matters if you reverse "30" and "87" but a subtle reason why you might want to reverse them. See http://www.bcae1.com/relays.htm for much more info.

As 67Dart273 says, it can matter if you wire the coil backwards, not for the coil itself but for an internal "spark arresting diode", if present. Some relays suggest you provide such an external diode if not present. Sometimes, a diode is in the relay's base, or the clamp may instead be a resistor. See above link for photos.

Terminal numbers are a standard, DIN 72552 (http://en.wikipedia.org/wiki/DIN_72552) originally German, now world-wide. It defines most common automobile connections with standard numbers, and helps a lot when reading the schematics for my 80's M-B cars or newer U.S. cars. Standard "Bosch" relay terminal numbers appear to conflict with DIN 72552, which lists supply on "87" and NO output on "87b" (no "30" exists for relays). Re coil terminals, "86" = "coil+" and "85" = "coil-" (usually directly grounded, though via NSS if a starter relay).

It seems we finally caught 67Dart273 in error. If you applied positive to "85" and grounded "86", the diode would bypass the coil so the relay wouldn't actuate and the diode would probably melt. The diode blocks flow from "86" (actuate) to "85" (ground) when the coil is "ON" and flows the other way when the coil switches off to dissipate "kick-back" voltage from inductor switch-off, which is how ignition coils work, but we don't want sparks in our relay.

You can always find conflicting info on the web. One site (http://www.accessconnect.com/car_relays.htm) shows "85" as coil+ and "86" as coil-, with a diode going the other way (works for that wiring). I doubt one could find such a commercial relay, but the first link above has a photo of a relay base with diode installed reversed (from these audio bozo's?). Of course, for a resistor clamp the coil polarity doesn't matter.

 

[RedFish]

Typical bosch 30 amp relay wont handle the load that starter needs for very long.
So long as the engine starts fairly easy no problem. First time something goes wrong causing you to run the starter for any length of time, the relay will melt down internally. The contacts inside aren't that large.

 

[BillGrissom]

Typical bosch 30 amp relay wont handle the load that starter needs for very long.
So long as the engine starts fairly easy no problem. First time something goes wrong causing you to run the starter for any length of time, the relay will melt down internally. The contacts inside aren't that large.

Not true. The 30A "starter relay" only needs to actuate the "contactor" which is a much bigger relay (~400A) inside the starter. My new relay box is from a 95-99 Jeep Grand Cherokee with Mopar Magnum engine and starter, and am using a Magnum mini-starter in my Dart, so everything is the same as in the Jeep (except NSS, but doesn't matter). BTW, if you are picking parts, the same relay/fuse boxes were in 6-cyl Jeeps, though relay labels varied slightly.

My 96 Voyager uses the same standard 30A automotive relay as "starter relay". My 2002 T&C may use a half-size relay (forgot). In any of these cars, one can actuate the starter by simply removing the relay and jumpering "30" to "87", but insure tranny is in "P" or "N", and don't stand in front.

 

[RedFish]

So the relays contacts don't need to be anywhere near the rating of the wires attached to it. If that was true the Bosch type relays connectors would have big honklin' lungs with screws to attach most any size wire.
Funny how one member here will say Chrysler was cheap in electronics and didn't do a dime thing more than they had to. Another member will suggest Chrysler wasted money in providing adequate starter relays. Same as their horn relay would have worked.
But hey, If yall can figure out how to attach adequate wires to a Bosch relay that will hold a starter engaged for any length of time... good luck with that.

 

[67Dart273]

First there are big differences between "Bosch style" relays. The ol' quality thing

Second, I've actually examined as many as 50? Mopar starter relays, and probably 15 or so various Bosch style. The contacts appear to be very similar. I do realize that's a subjective thing.

It "just might be" that a typical Bosch might not live 100K miles with an antique Mopar starter. On the other hand if you ARE running a mini, I'm sure a Bosch will handle it jus' fine.

 

[RogerK]

First there are big differences between "Bosch style" relays. The ol' quality thing

Second, I've actually examined as many as 50? Mopar starter relays, and probably 15 or so various Bosch style. The contacts appear to be very similar. I do realize that's a subjective thing.

It "just might be" that a typical Bosch might not live 100K miles with an antique Mopar starter. On the other hand if you ARE running a mini, I'm sure a Bosch will handle it jus' fine.

A lot of great, informative responses. Thank you all. I already swapped in the Magnum mini starter in the spring so I shouldn't have any issues with the relay swap. :cheers: